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• Published: 25 July 2023

Emotional processing in bilinguals: a systematic review aimed at identifying future trends in neurolinguistics

• Humera Sharif 1 &
• Saqib Mahmood 1  

Humanities and Social Sciences Communications volume  10 , Article number:  438 ( 2023 ) Cite this article

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• Language and linguistics
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This review is one of the first studies to discuss the status of research on emotional processing in a healthy bilingual brain. Few articles about emotion and cognition coupling have examined how the bilingual brain differs in processing emotional stimuli from the monolingual brain in neuroimaging studies. Having diverse perspectives, tools, and methodologies in interdisciplinary research can help build our understanding of the connection between the mind, language, and emotions. This systematic review uses Moher et al., (2015) PRISMA-P to synthesize relevant publications. In this review study, we discuss common discrepancies, the techniques used to elicit data and the objectives of the emotion and cognition interaction in neuroimaging, psychophysiological and cognitive paradigms. Our findings suggest the focus of future research on simultaneous bilinguals, extended narratives instead of decontextualized stimuli and comparison of different modalities. We provide valuable insight for neurolinguistic researchers in regard to the various limitations in the existing literature that hinder the successful integration of emotion and language studies into the field of neurolinguistics.

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Introduction.

Emotions are a fundamental aspect of human characteristics, and they are intertwined with social meanings and shared public practices (Goodwin et al., 2012 ; Robillard et al., 2019 ). Emotional processing can be observed through instinctive facial body responses, countenance, and physiological and cognitive factors. How emotional stimuli are processed has been studied extensively by various disciplines, including physiology, cognitive science, and neuroscience. Altarriba ( 2013 ) emphasized the importance of psychological and linguistic factors in examining the affect-language interface. Hinojosa et al. ( 2019 ) conducted a systematic review of the neural basis of emotional processing during emotion-language comprehension. Still, it left the need to investigate how affective neurolinguistics might guide future trends in emotion-language interaction research in bilinguals.

Bilinguals outnumber monolinguals (Grosjean, 2010 ). First and second languages in bilingual speakers’ brains frequently compete for emotional input, and research has shown that one language may supersede the other in eliciting emotions. Sometimes, bilinguals may even outperform monolingual peers in recognizing emotional inputs (Altarriba & Morier, 2004 ). With globalization leading to more diversified, multicultural societies and bilingual families, it has become crucial to investigate how emotional stimuli affect language processing in the bilingual brain.

The impact of bilingual experience on human behavior and neurological function has been extensively studied (Caldwell-Harris, 2014 ). However, more research is needed on how emotions are processed in the brain when a bilingual or multilingual individual receives verbal inputs that support emotional inducements. A substantial connection between cognitive control and overall L2 proficiency has been observed in various research. In late bilinguals, respective languages may be differentially embodied (Pavlenko, 2005 ). There is a significant connection between cognitive control and overall second language proficiency, and bilingualism enhances cognitive flexibility and communicative capacity. Additionally, bilingualism boosts cognitive reserves and productivity as people age (Bialystok et al., 2012 ).

Given the interdisciplinary nature of research on affective processing in bilinguals, studies might differ in stimuli, theoretical approaches, and techniques, leading to inconsistent findings regarding emotional processing. Moreover, publications on this topic may appear in different domains and journals, making it challenging to keep track of all the research. Therefore, this review aims to synthesize up-to-date findings on affective processing in healthy bilinguals across three paradigms: cognitive, psychophysiological, and neuroimaging. Further cross-disciplinary studies with different techniques and populations are necessary to advance our understanding of this complex topic. The goal is to lay out directions for future research in neurolinguistics and investigate how advancements in the behavioral sciences can benefit research on neurolinguistics.

To limit the scope of this review, we focused on receptive language processing (reading and listening) and excluded studies on affective processing influencing language production and those on second-language learning and the emotion-language interface (DeDios-Stern & Ventura, 2021 ; Antia et al., 2021 ; Brouwer, 2021 ; Jones et al., 2021 ; Zarbafi, 2020 ; Corrêa et al., 2020 ; Cumbe et al., 2020 ; Bemath et al., 2020 ; Nidoo & Gokool, 2020 ; Ravaldi et al., 2020 and many others from 2010 to 2019).

Emotion and cognition

Emotion and cognition do not embody separate neurological systems; brain regions involved in emotional processing are also involved in cognition, and vice versa (Pessoa, 2008 ). Mondal ( 2022 ) conceptualizes the formal similarities between linguistic representations of emotion and perception for integrating perceptual and cognitive representations. According to Connell and Lynott ( 2014 ), cognitive representations are structures and schemas realized as collections of neural circuits essential for assessing things, events, and circumstances in the outside world. Hence, cognitive depictions incorporate experiences and ideas and can initiate again with the same experience beforehand, consequently affecting other neural functions. Perceptual and linguistic illustrations denote cognitive depictions coded and embodied in language and sensory systems; moreover, emotions are depicted in linguistic codes when expressed in language.

Meanwhile, the pertinence between emotions and perception can help reveal their characteristics and attributes. On the one hand, perception is frequently separated from the rest of cognition in a hefty portion of modern-day cognitive science. Conversely, Pessoa ( 2022 ) showed that perception and cognition have significant linkages and connections. The linguistic encoding of emotive representations plays a distinct part in elucidating trends of interactions between perception and cognition, provided that linguistically encoded representations of emotion are cognitive representations. These representations also exert a sensory character due to comparisons between emotion and perception. The processing and referential dimensions in cognitive processes that regulate the computational complexity of attending to only pertinent points from within a quagmire of unnecessary detail in the perceptual surroundings can be better comprehended by studying differences across the perception and cognition continuum (Phelps, 2006 ). This process becomes challenging for bilinguals.

The ability to speak more than one language alters an individual’s perspective and understanding of events occurring in their surroundings (Robinson & Altarriba, 2014 ). Bilingual brains are encoded with two languages: one language dominates the other one in most cases. By examining findings from reaction time, eye-tracking, functional magnetic resonance imaging, and event-related potential research, previous studies have investigated how language proficiency in one of two languages influences cognitive control and emotion, both of which are essential components of human interaction (Hinojosa et al., 2019 ; Hsu et al., 2015 and Imbault et al., 2021 ). We suggest that managing multiple languages has a profound effect not only on cognitive control and emotion separately but also on the interplay between the two. Language-cognition interaction is pertinent; the presence of two languages may drive different cognitive abilities. Processing and referential dimensions of cognition attend readily available linguistic codes on the threshold continuum (Paradis, 2004 ), such as responding to a stressful event becoming a different experience for bilinguals than monolinguals. Thus, examining the role of proficient and non-proficient linguistic codes guiding emotional perception becomes essential.

Emotion cognition and brain structures

Emotions affect various cognitive processes, including working memory, cognitive control, learning, episodic memory, decision-making, spontaneous thought, and attention (Todd et al., ( 2020 )). An unpleasant emotional state can also reduce working memory, and individuals with depressive symptoms may have difficulty regulating their emotions effectively. Emotional arousal can enhance associative memories for features, colors, and location and lead to spontaneous thoughts and quick decisions without using rationale. Positive emotions involve a broadening of emotions.

Phelps ( 2006 ) suggests that animal neural models of emotion indicate that brain structures connected to emotional processes also heavily interrelate with other brain systems associated with cognition. One of these structures is the amygdala, an almond-shaped structure located in the medial temporal lobe next to the hippocampus. Klüver and Bucy ( 1937 ) proposed that lesions in the medial temporal lobe played a role in displaying odd behaviors while observing monkeys. Later, Weiskrantz ( 1956 ) demonstrated that damage to the amygdala within the medial temporal lobe caused various behaviors, known as Kluver-Bucy syndrome.

It is clear that the amygdala automatically processes emotions and can stimulate numerous cognitive functions. Research on animals has shown that specific subcortical pathways can detect emotion and alert the amygdala before the actual response. These findings suggest that emotions are processed before comprehension (Zajonc, 1984 ).

According to de Mendoza ( 2008 ), the amygdala can modify facial expressions in response to emotional words. Furthermore, task demands can also affect how the amygdala responds to social groupings defined by race (Kuchinke et al., 2005 ). This research highlights the importance of examining cognitive abilities to understand brain systems and emotion processing (Skrandies, 2011 ).

Methodology

We systematically reviewed the current literature to answer the following question:

RQ. How can current studies on bilingualism and emotion coupling investigated in multiple disciplines influence future research in neurolinguistics?

We further set the following objectives concerning this research question:

To identify various recent advances assessing emotional processing in healthy bilinguals in psychophysiological, cognitive and neuroimaging research paradigms,

To investigate the stimuli, the objectives and techniques used to assess emotion- language interaction in healthy bilinguals,

To identify the gap for future research agenda for emotion and bilingualism in neurolinguistics.

Literature search and study selection

We followed a research strategy based on Moher et al., ( 2015 ) PRISMA-P checklist, using systematic and explicit methods. Our methodology included defining a search strategy, eligibility criteria, screening process, and plans for data synthesis. We collected administrative data such as title, publication date/year, authors, and introduction data, including study objectives, stimuli, sample/participants, and outcomes.

Search strategy

Initially, we queried the WorldCat database. We chose it because it is the most extensive database for all the research papers published in well-reputed journals indexed by Web of Science and Scopus. Then, we selected PubMed because it was needed in our area of interest. Neurolinguistics integrates the disciplines of Language and Neuroscience (purely medical), so we ensured that all the relevant studies to answer our questions were gathered published from 2010 to 2022, considering the recent developments and current focus of inquiries in other paradigms; the reason was to avoid the risk factor of suppressing our focus on neurolinguistics by relying too much on other paradigms.

Eligibility criteria

Guided by our research question, we selected only the research articles focused on emotion processing and cognition in bilinguals while perceiving a language and excluded the studies related to speech production or speaking abilities. The research articles about language disabilities were also excluded. We also excluded the affective studies employing introspective approaches and other review articles in behavioral research and emotion studies on foreign/second language learning investigating the role of emotions in language learning. Articles on inhibitory control were excluded to avoid excessive cognitive paradigms. Only memory recall studies were considered, as the given definition (pg# 10) described it as an essential component of the cognitive paradigm. We only selected the articles that implicitly and explicitly included the key terms (emotion, cognition/neuroscience, bilingualism). We set the search strings such as emotion, cognition and bilinguals; emotion, cognition and EEG; emotion, cognition and neuroimaging and emotion, neuroscience, and bilinguals.

Data and outcome articles

Two hundred ninety studies were gathered from the WorldCat database with the variable neuroscience and the 338 studies when neuroscience was replaced by cognition. Twenty-three studies were yielded on PubMed when neuroscience was used, and the variable cognition produced 105 results. The initial search yielded a total of 756 results. A careful screening excluded all the repeated articles, and 756 were reduced to 457. Further screening after reading the titles excluded all the book chapters, review studies, the studies missing any one or all of the variables from the search strings, and studies about language disorders and acquired the refined number 122.

A detailed screening was done by reading abstracts and articles in detail. The articles explicitly addressing emotion-language coupling in bilinguals received further scrutiny. The articles with no primary focus on emotional processing or bilingualism were excluded. Hence, the final number scrutinized for the review was 37: 19 from the cognitive, 07 from psychophysiological and 11 from neuroimaging studies. A cross-check and review by the second author suggested 16 more articles to consider for the review because their contribution to investigating the answers to the current study’s objectives seemed significant. These articles belonged to the introspective paradigm, executive functions and two review studies. Nevertheless, considering the exceeding word limit of the current review, we added only a table summarizing the findings of these 16 studies with various themes (Table 1 ). All in all, the total number of articles reviewed in this study was 53 (Fig. 1 ).

An overview of search protocol based on PRISMA recommendation statement.

Data collection and coding process

The data was collected by a PhD scholar in neurolinguistics. The data was coded by hand, and an associate professor in applied linguistics cross-checked the initial screening. He also re-examined the detailed review and critical evaluation. The suggestions were considered and incorporated after discussing the reliability of the agreements and disagreements between them.

Review of different approaches

Psychophysiological approaches.

Physiological measures can provide valuable insights into behaviour, cognition, and health interaction. One of the most commonly used approaches is the psychophysiological approach, which relies on physiological markers of autonomic arousal such as electrical conductivity of the skin, activation of smile or anger muscles, heart rate, and others (Palvenko, 2012).

Studies in the psychophysiological approach have focused on exploring the interaction between emotion and language cognition in late bilinguals. These studies examined emotional resonance through various techniques, such as comparing emotional response in self-report and psychophysiological arousal (Caldwell-Harris et al., ( 2011 )), response in facial motor and skin conductance (Baumeister et al., 2017 ), galvanic skin response (Jankowiak & Korpal, 2018 ), pupil dilation (Toivo & Scheepers, 2019 ), and electrodermal activity (Grégoire & Greening, 2019 ). The findings of these studies suggest a consensus of reduced emotional resonance in L2. However, the reviewed research works utilized different stimuli, including listening to emotional phrases (Caldwell-Harris et al., ( 2011 )), a stimuli corpus consisting of 345 words associated with the concept of happiness and anger (Baumeister et al., 2017 ), emotion-laden words in visual and auditory modalities (Jankowiak & Korpal, 2018 ), and high- versus low-arousing words in both L1 and L2 with lexical confounds such as length, frequency, emotional valence, and abstractness (Toivo & Scheepers, 2019 ).

These studies have concluded that there is weak emotional elicitation in L2; the main reason could be the less frequent use of L2 than L1 in its non-native setting. Late exposure to the second language requires an increased threshold to access L2 codes, resulting in reduced access of the cognitive set-up to emotional input in L2. Additionally, bilinguals in languages with the head-initial parameter (the head of a phrase precedes its complement) or vice versa may also drive emotional intensity differently than in languages with the same language-headedness parameter. Examining this phenomenon with the same objectives and techniques but with different populations born and raised in different sociocultural settings is necessary.

Baumeister et al., 2017 study partially supported decreased facial motor and skin conductance responses to emotional words in L2. However, the study did not consider how different modalities and distinctions between emotion-laden and emotion-label words influence emotional response in L2. The study results of Jankowiak and Korpal ( 2018 ) suggested investigating the question that emotional processing may have been modulated by both language and modality, leaving the gap in their study with an unaddressed area of emotion-label narratives processing emotions in bilinguals. Toivo & Scheepers, 2019 findings suggest that the results might have changed by changing the stimuli of single words with a cohesive narrative.

The section discusses the use of physiological measures in studying the interaction of behaviour, cognition, and health. The studies reviewed in this paragraph focus on emotion and language cognition interaction in late bilinguals. The studies utilized different stimuli and techniques to examine emotional responses in L2, which resulted in a consensus of reduced emotional resonance in L2. The studies suggest that reduced access of the cognitive set-up to emotional input in L2 might be the reason. The paragraph also highlights the need to examine this phenomenon with different populations born and raised in different sociocultural settings and languages with different language-headedness parameters. The studies reviewed need to address specific areas of emotion-label narratives processing emotions in bilinguals.

Cognitive approach

The cognitive theory asserts that how we think guides our feelings and behaviors, encompassing memory, comprehension, motivation, and perception. This paradigm encompasses memory recall, congruence effects, and interference effects (Pavlenko, 2005 ).

Cognitive psychology research focuses on memory recall of emotional words in L1 and L2. Ferré et al. ( 2010 ) found that emotional words were recalled better than neutral words to a similar degree in both languages of bilinguals. It differed from a previous study by Ayçiçegi and Harris ( 2004 ), who observed greater recall of emotional words in L2. Ferré et al.’s Spanish-English bilinguals ( 2010 ) were mixed-context learners. They claimed that neither context of acquisition (CoA) nor typological distance and age of acquisition (AoA) reduced the’recall of emotion words in L1 and L2. However, they did not control for the type of emotional words, such as positive, negative, and neutral, and mixed them up. Short- and long-term memory remained unaddressed variables in both studies.

Bridging this gap, Sun et al. ( 2018 ) used L2 emotional words in the context of pictures and associated monetary rewards and punishments with positive and negative emotions, respectively. The positive words and rewards were better recalled in short intervals, and punishment and negative emotions were more associated with long-term memory recall. The results could have been explained in terms of abstract and concrete nouns, which may have been a factor driving the results. The vital aspects of language proficiency and working memory interaction were explored in all three studies.

Ma et al. ( 2020 ) focused on the difference in emotional working memory by examining the performance of Chinese-English proficient vs non-proficient bilinguals on the delayed matching-to-sample task. Proficient bilinguals scored higher in matching sets of numbers (the emotional letter) to the letter displayed on the previous screen in an E (emotional) N-back test. In an N-back test, a sample letter appears first, and then the comparison set appears later on the screen; participants must match the emotional stimuli from the set of comparison stimuli to the sample stimuli. The findings supported the notion that proficient bilinguals may have an advantage in their cognitive abilities. The second language also has a significant role in decreasing and lowering negative emotions.

Jansson and Dylman ( 2021 ) investigated second-language effects on emotionality by examining experienced vividness. Emotionality was reduced when negative experiences were recalled in L1 and L2, whereas experience vividness was decreased only in the second language. Their findings contradict Dylman and Bjarta (2018), who observed increased distress when participants read and answered the negative text after reading in L1. It might be due to memory recall control in their study, so it becomes crucial to observe the associated experiences in future studies.

In conclusion, the recall of emotional words in bilinguals is a complex phenomenon affected by various factors such as emotional word type, short- and long-term memory, language proficiency, working memory, and the context of acquisition. While some studies suggest that emotional words are recalled better than neutral words in both L1 and L2, others suggest that emotional word recall may be influenced by the emotional context in which they are presented. Additionally, language proficiency plays a significant role in emotional word recall, with proficient bilinguals performing better on emotional working memory tasks. Further research is needed to clarify the impact of these variables on emotional word recall and better understand the underlying mechanisms of emotional processing in bilinguals.

Congruence effects: affective priming

The processing of affective valence is observed when word/nonword match primes and targets in valence, and it is known as congruent because it is expected that congruent conditions, such as negative-negative, would produce faster reaction times. Congruence effects are examined in a lexical decision task.

Alvarado and Jameson ( 2011 ) concluded their study with a consensus of about 15 emotion terms, but they found a difference in terms of “shame” and “anguish.” The results showed similarity in the structure of emotional space across highly diverse cultures, suggesting that the sociocultural setting may be less important than other factors, such as linguistic factors, which may lead to differences in emotional processing. These findings support the critical evaluation of psychophysiological approaches for the role of language headedness (the head of a phrase position concerning its complement) as more Important.

Ponari et al. ( 2015 ) selected highly proficient bilinguals in their second language (English) to examine affective priming. The participants were of different ages of English acquisition and contexts of English language use and varied in frequency. The results indicated that the participants showed the same facilitation in processing emotionally valenced words as native English speakers, which contradicts previous studies concluding that the age of language acquisition affects affective processing. This finding suggests that affective processing is directly related to language proficiency and dominance and not to age of acquisition (AoA), the context of language learning (CoLL), frequency, or native language background, which directly affect language proficiency but not emotional processing.

El-Dakhs and Altarriba ( 2019 ) investigated this assumption by presenting auditory stimuli through classroom computers. They found that participants with increased L2 exposure outperformed non-proficient bilinguals in processing emotionally valanced content and emotional word types, which suggests that the context of language learning also affects emotional processing. Seniors who studied English as the mode of instruction for four years and used English for communication even outside the class outperformed Arabic students. The significance of sociolinguistic context to better understand the root of cognitive differences was attempted in the study of López et al. ( 2021 ) on a language brokering experience tied with L1 proficiency. Their study supported the theory of language embodiment (Palvenko, 2002), suggesting that low L1 proficiency coupled with negative feelings tied to language brokering experience moderated the Simon Task. These findings suggest that bilingualism with socio-contextual and socio-emotional language experiences induces differences in performance and emotional processing.

Imbault et al. ( 2021 ) investigated the priming effect using a large dataset of 2628 English valenced and arousal words. Their findings were consistent with previous studies (Ponari et al., 2015 ; El-Dakhs & Altarriba, 2019 ), and they argued that there is a significant relationship between word frequency and L2 proficiency. All three studies agreed on the time spent in the native language context. It is not a direct emotional processing factor; it somewhat improves language proficiency, which may influence emotional processing.

In Altarriba and Basnight-Brown’s ( 2011 ) study, an affective Simon task was administered to both English-speaking monolinguals and Spanish-English bilinguals to investigate the processing of valence and emotionality. The results indicated that bilinguals showed an advantage in congruency effects on negative emotions only, whereas both positive and negative emotion-laden words exhibited significant Simon effects. Additionally, Incera et al. ( 2020 ) found that bilinguals had an advantage in processing taboo words compared to neutral words, despite monolinguals outperforming bilinguals in emotional processing. However, it is worth noting that their study only used emotion-laden words, which may yield different results than emotion-label terms.

Morawetz et al. ( 2017 ) discovered an advantage of L2 in emotional regulation using images with content and emotion labelling. While there were differences in the stimuli used in these studies, the consistency in findings suggests the robustness of bilinguals’ advantage in emotional regulation and less emotional processing. Kazanas and Altarriba ( 2016 ) suggested that this distinction of word types might be most pronounced in a person’s dominant language. Their study on Spanish-English bilinguals found that negative words elicit emotions slower than positive ones.

Another study conducted by Bromberek-Dyzman (2021) investigated the difference in word type operation between two groups of bilinguals: Polish-English and Romanian-English. The results indicated facilitation for emotion-laden words (adjectives as chosen stimuli) in processing and established that the lexical proximity between two languages modulates affective responsiveness.

In order to confirm the results of these paradigms, further research on a comprehensive discourse consisting of strings of lines is necessary. It should be counter-checked with studies using neuroimaging techniques in the paradigm of neurolinguistics.

In conclusion, the processing of affective valence in bilinguals is a complex phenomenon influenced by various factors such as language proficiency, age of acquisition, frequency of language use, sociolinguistic context, and word type. Previous studies have yielded conflicting results regarding the effects of these factors on emotional processing in bilinguals. However, recent research suggests that language proficiency and dominance may be more crucial in affective processing than the age of acquisition or sociocultural context. Additionally, the type of emotional stimuli presented, whether emotion-laden words or emotion labels, may play a role in bilingual emotional processing. More research is needed to fully understand the complexities of affective processing in bilinguals and how different factors contribute to these processes.

Neuroimaging studies

Neuroimaging studies use functional magnetic resonance imaging (fMRI), positron emission tomography (PET), or event-related potential (ERP). Latencies measure the time course of processing, with shorter latencies indicating early processing. The letters N and P indicate the polarity of the component, with N indicating a negative peak and P denoting a positive peak, followed by a number suggesting a particular peak. N400 is observed during language comprehension for semantic processing and integration. The numerical value such as 100, 200, or 400 with N and P suggests that the responses are calculated at the peak value of 100, 200, or 400 ms.

EEG measures the brain’s pro-electric activity caused by neurons’ oscillation in response to emotional stimuli. Pavlenko ( 2005 ) reported that, until then, all neuroimaging studies of affective processing in bilinguals relied on ERP, trusting on early posterior negativity. A few studies published between 2015 and 2021 (Chen et al., 2015 ; Jeong et al., 2016 ; He et al., 2021 ) relied on fMRI or both fMRI and ERP. The ERP studies depended more on recording EEG than resting state EEG (Conrad et al., 2011 ; Sianipar et al., 2015 ; Jończyk, 2016 ; Vélez-Uribe, 2018 ; Vélez-Uribe & Rosselli, 2021 ; Sendek et al., 2021 ; Barker & Bialystok, 2019 ; Wu & Zhang, 2019 ).

Conrad et al. ( 2011 ) recorded the EEG of German-Spanish bilinguals to examine their sensitivity to their L2 by using decontextualized words. Results indicated no qualitative difference between positive and negative emotional stimuli, regardless of their L1 and L2. These findings were insufficient to establish a hypothesis about the role of L1 and L2 in emotional language cognition. So, another contribution came from Sianipar et al. ( 2015 ), who examined word processing effectively and semantically in L2 learners in four sessions employing a primed lexical decision paradigm spanning half a year of L2 learning. They observed improved sensitivity rates, accuracy rates, RTs, and N400 amplitude across sessions. The ERP data exhibited L2 valence effects more than neutral words across sessions. The findings also indicated a separate representation of the brain’s semantic and affective processing. It also suggested that proficiency level in L2 affects semantic and affective processing of words or narratives in L2. All these studies addressed the affective cognition of balanced bilinguals.

A significant study finding was different language processing ’n balanced and unbalanced groups in both languages. Therefore, Vélez-Uribe ( 2018 ) investigated the effects of language proficiency in emotional content processing, comparing balanced and unbalanced Spanish-English bilinguals. The results of valence effects advantage over neutral words were consistent in both languages (Spanish and English) in balanced groups only. The Spanish unbalanced group showed a larger Latent Positive Complex (LPC) for positive than neutral and neutral than negative. Chen et al. ( 2015 ) found smaller Late Positive Complex (LPC) amplitudes for positive words compared to neutral words in L1 Spanish-English bilinguals. In a subsequent study, Vélez-Uribe and Rosselli ( 2021 ) compared balanced and unbalanced Spanish-English bilinguals and found that emotional words were processed more efficiently than neutral words, with the balanced group showing delayed ERP latencies for L2 emotional words and the unbalanced group showing shorter latencies for L2 emotional words. These findings suggest that language proficiency and the context of language learning and use may influence emotional word processing. Ma et al. ( 2020 ) reported similar results using a physiological paradigm, supporting the hypothesis of cognitive advantages for proficient bilinguals. However, cross-disciplinary studies using different techniques and populations are necessary to understand better the interaction between emotion, language, and cognition in bilinguals. Additionally, the role of language dominance should be examined to determine whether brain representation differs based on language dominance, regardless of the first language and other factors.

The studies discussed thus far only investigate emotional words; it remains unclear how different categories of emotional words, such as abstract and concrete affective words, emotion-label and emotion-laden words, and metaphorical and figurative words, affect bilinguals’ emotional word processing. Wu and Zhang ( 2019 ) explored this question by examining the conflict processing of positive emotion-label and positive emotion-laden words in Chinese-English proficient bilinguals using a Flanker task. They found that positive emotion-laden words elicited different brain activations than positive emotion-label and neutral words. However, this study only investigated positive terms, and including negative words may yield different results. Furthermore, taboo words may also affect emotional word processing differently. Sendek et al. ( 2021 ) addressed this issue by using only taboo words in American and British English and found a significant difference in social threat perception between the two groups. However, the results may vary based on other contextual cues, such as pragmatic and motivational factors.

Barker and Bialystok ( 2019 ) investigated emotional and cognitive mechanisms using an n-back test to compare monolinguals and bilinguals. They found that emotional distraction had a more significant effect on monolinguals than bilinguals. These results align with previous studies that have reported a bilingual advantage in affective processing across different paradigms (Baumeister et al., 2017 ; Jankowiak & Korpal, 2018 ; Ma et al., 2020 ; Sharif & Malik, 2022 ; Toivo & Scheepers, 2019 ). These findings provide a platform for future research to improve emotional discourse practices in therapy.

Wu and Zhang ( 2019 ) used positive emotion-label and positive emotion-laden words to investigate conflict processing in a Flanker task in Chinese-English bilinguals. They found that positive emotion-laden words elicited different brain activations than positive and neutral emotion-label words. These results were consistent with Bromberek-Dyzman et al. ( 2021 ), who investigated congruent effects using affective priming tasks. Chen et al. ( 2015 ) examined emotional processing using ERP and fMRI and reported a positive word processing advantage for neutral and negative words. In their study, the left superior frontal gyrus processed negative emotional words. Different brain activation patterns were involved in the reduced processing of positive emotional words in L1 and L2 (middle occipital gyrus and left cerebellum), revealing a complex picture of emotional word processing in bilinguals. Further investigation in this area may help neurosurgeons and physicians to decide on the brain areas engaged in emotional regulation to keep intact, considering patients’ language dominance while removing tumours.

Jeong et al. ( 2016 ) examined the underlying neural mechanism involved in L2 communication vs L2 description, recruiting the left posterior supramarginal gyrus. The findings revealed that L2 communication was sensitive to oral proficiency and L2 anxiety, recruiting the left posterior supramarginal gyrus, indicating that L2 communication relies on social skills. Activation in the left middle temporal gyrus increased with L2 proficiency, and activation in the orbitofrontal cortex decreased as the L2 anxiety level increased. These results support the hypothesis of sociocultural context involvement in the intersection of language, emotion and cognition. Further research in this area is required to improve foreign language teaching strategies and course design.

He et al. ( 2021 ) investigated the neural mechanisms underlying language and emotional interaction in decision-making during a gambling task. They observed avoidance mechanisms for negative feedback in L2 mediated by the dorsolateral prefrontal cortex and enhanced hippocampus activation for win feedback in L2. A significant limitation of the studies is their use of decontextualized stimuli consisting of only words. It calls for more research by adding extended narratives with different emotional valences.

Hsu et al. ( 2015 ) tried contrasting emotional responses to literary reading in L1 and L2 bilinguals with three emotional valences in an fMRI study. The study found that L1 bilinguals had a more robust hemodynamic response to ‘happy’ passages than neutral ones. Furthermore, it indicated that emotional processing was more substantial and differentiated in L1 than in L2, which was consistent with the findings of behavioural studies (Jankowiak & Korpal, 2018 ; Ma et al., 2020 ; Sharif & Malik, 2022 ). Jończyk et al. ( 2016 ) conducted a study in which Polish-English bilinguals and native English monolinguals were compared using sentences that ended semantically and affectively with congruent and noncongruent adjectives. The study found that N400 amplitude was overall more negative in L1 than in L2 in bilinguals. In monolinguals, the N400 congruity affect appeared earlier at the onset, supporting previous results that negative information is suppressed in L2 at the earlier stage, thus requiring less evaluation at the later stage. Jończyk ( 2016 ) added a pragmatic twist to uncover differences in cortical activation to affective adjectives in L1 and L2 through an fMRI study. This study observed the difference between N400 and LPC modulations, indicating enhanced affective response in L1, which was again consistent with previous studies (Hsu et al., 2015 ; Jankowiak & Korpal, 2018 ; Ma et al., 2020 ; Sharif & Malik, 2022 ). These findings raise questions for multilingual and bilingual speakers raised in different social and cultural settings. Including and comparing different types of bilinguals and comparing bilinguals speaking languages with different Universal Grammar parameters will significantly contribute to the arena of affective neurolinguistics.

The studies reviewed in this text focus on the intersection of emotion, language, and cognition in bilingual individuals. They used various neuroimaging techniques, including fMRI and ERP, to investigate how language proficiency affects emotional word processing. The studies suggest that balanced bilinguals show better cognition for emotional words than neutral words, and language proficiency and context of language learning and use may influence emotional content processing. Additionally, studies have begun to explore how emotional words belonging to different categories, such as abstract and concrete affective words, emotion-label and emotion-laden words, and metaphorical and figurative words, affect cognitive processing in bilinguals. However, more cross-disciplinary research is needed to fully understand the complex relationship between emotion, language, and cognition in bilingual individuals. The studies reviewed here highlight the importance of examining language dominance and considering contextual cues in future research.

In this section, we have discussed the findings summarized above to find precise answers to the objectives of this review study. The first four sections discuss research objectives one (Table 2 ) and two. Following these four sections, the last section lead to the final discussion on future works in bilingualism in neurolinguistics.

Language dominance to take over L1/L2 metaphor

The results demonstrate two distinct processing patterns: bilinguals outperforming monolinguals and proficient bilinguals displaying an advantage over non-proficient ones. These findings reveal two complementary patterns of interaction between emotion and cognition: L1 advantage in emotional processing and L2 advantage in emotional regulation. The L1 advantage is attributed to increased automaticity and more facilitation in emotional processing (Incera et al., 2020 ). Conversely, reading and processing a negative text in the L1 can increase distress (Dylman, Bjärtå ( 2019 )). The parallel L2 advantage was found using L2 to decrease negative emotions (Tse & Pu, 2012 ). Reduced automaticity is believed to assist in emotional regulation, as demonstrated by decreased facial motor response and skin conductance response to emotional words in L2 (Baumeister et al., 2017 ), decreased Galvanic Skin Response (Jankowiak & Korpal, 2018 ), increased pupil dilation supporting reduced emotional resonance in L2 (Toivo & Scheepers, 2019 ), and reduced experienced vividness in L2 (Jansson & Dylman, 2021 ).

Bilinguals exhibit enhanced cognitive abilities that assist in reducing emotionality (Ferré et al., 2010 ). They demonstrate an advantage in congruency effects on negative emotions (Altarriba & Basnight-Brown, 2011 ), emotional regulation, and reduced automaticity (Morawetz et al., 2017 ). It is worth noting that trait anxiety decreases inhibitory control accuracy in bilinguals but not monolinguals (Ouzia et al., 2019 ). Monolinguals were observed to surpass bilinguals in detecting and identifying emotions (Incera et al., 2020 ).

Highly proficient bilinguals process emotions similarly to L1 speakers (Alvarado & Jameson, 2011 ), and proficient L2 learners outperform non-proficient bilinguals in processing emotions (Ponari et al., 2015 ; El-Dakhs & Altarriba, 2019 ). Additionally, bilinguals with native-like command process working memory better than less proficient ones (Ferré et al., 2010 ). An emotional word processing advantage has also been observed over neutral word processing (Ferré et al., 2010 ).

Psychophysiology and cognitive psychology studies agree that bilinguals outperform monolinguals in different cognitive tasks (Ferré et al., 2010 ; Altarriba & Basnight-Brown, 2011 ). L2 advantage is observed in reducing emotionality in decision-making tasks and regulating negative emotions to make rational choices. The language dominance of bilinguals can affect their moral dilemmas, as observed in the study by Ma et al. ( 2020 ). These findings suggest that stress should be shifted to language dominance, given that a person can be dominant in their L2 and not L1. The dominant language controls cognitive abilities. Hence, future research should rely on language dominance instead of the L1 and L2 debate (Table 2 ).

Considering the role of modality

Modality is another attention-demanding factor in research on the coupling between emotion and language. Modality refers to the sensory channel through which information is perceived or processed, such as visual, auditory, tactile, olfactory, or gustatory modalities. In language, modality refers to how information is expressed or communicated. For example, spoken language is an auditory modality, while sign language is a visual modality. In cognitive science, modality refers to the specific way in which information is processed, organized, and represented in the brain. It concerns how different modalities (e.g., visual, auditory, etc.) affect cognition and perception and how the brain integrates and processes information from different modalities.

Modality was identified as a limitation of the study conducted by Baumeister et al. ( 2017 ). Subsequently, only Ouzia et al. ( 2019 ) and Jankowiak & Korpal ( 2018 ) indicated that emotional processing might exhibit variation when examined using different modalities. However, due to the limited number of studies, further research is needed to confirm these findings.

Stimuli limitation

The reliance on single-word processing is a disadvantage in the studies documented above. Only Caldwell-Harris et al., ( 2011 ) utilized emotional phrases, Jankowiak and Korpal ( 2018 ) used emotion-laden narratives, and Hsu et al., ( 2015 ) included short passages from the Harry Potter books. Since these studies were limited in number, their findings cannot be generalized. Decontextualized single words elicit weak emotions. In future research, there is a need to examine emotional processing using a cohesive discourse that represents a complete thought. Co-text, in interaction with context, evokes emotions within a naturalistic environment. The reason for neglecting emotion and cognition research is that it is challenging to simulate realistic interactions in the lab. The context can be manipulated using discourse with different modalities, such as pictorial or video representation.

Studies using emotion-label and emotion-laden stimuli are scarce, emphasizing the need for future work. Studies using valenced and arousal stimuli differ in their number and type of stimuli, lexical confounds, objectives, and methodological considerations (Altarriba & Basnight-Brown, 2011 ; Caldwell-Harris et al., ( 2011 ); Alvarado & Jameson, 2011 ; Toivo & Scheepers, 2019 ; Imbault et al., 2021 ). Therefore, their findings cannot be generalized. Also, inconsistent findings of memory-recall studies (Ferré et al., 2010 ; Ayçiçegi and Harris ( 2004 )) indicate a broad spectrum for future research on stimulus types. It establishes the need for extensive research to establish a consensus-based theoretical foundation.

The findings discussed in these sections are from the paradigms of psychophysiological and cognitive studies, explaining that regardless of the stimuli used and their focus and population, they all investigated behavioural and physiological responses in the groups of L1 and L2. Cross-task neuroimaging studies should examine these processes with the same procedural characteristics to see whether they differ in findings or if the results remain the same. Few studies in recent works have taken up this area of inquiry, as summarized in the section on neuroimaging studies and discussed in the next section.

Neuroimaging from the perspective of neurolinguistics

The neuroimaging studies in this review addressed different questions. The studies included techniques of ERP and fMRI to obtain brain images during emotional processing. FMRI measures hemodynamic changes induced by regional changes in neural activity with high spatial resolution. These techniques help identify the brain regions activated during emotional processing. Electroencephalogram (EEG) in ERP studies measures electric signals with high temporal resolution. It calculates the potential generated by the neurons in the brain in response to an event (external stimuli).

Chen et al. ( 2015 ) addressed the factor of language dominance in emotion content processing in their study. This study sets a comparison between decontextualized positive emotional words and neutral words. It seeks attention from future researchers to investigate the role of language dominance in emotional processing in a possible naturalistic setting and by utilizing stimuli consisting of cohesive discourse and complete thought. Only one study tried to bridge the gap and used passages from literary reading to compare the processing of happy and neutral stimuli (Hsu et al., 2015 ). It concluded that there was a more robust hemodynamic response to happy words than neutral ones. Among all three paradigms, only one study compared balanced and unbalanced groups to examine emotional processing, and only one study compared balanced and unbalanced bilinguals in English and Spanish (Vélez-Uribe, 2018 ). More research is needed to investigate other languages to draw more conclusive results regarding emotional processing in the brain of balanced and unbalanced bilinguals. A much-needed area of inquiry is the processes underpinning emotion-language coupling and processing in the brain of balanced and unbalanced bilinguals.

Jeong et al. ( 2016 ) collected underlying neural mechanisms showing the effects of L2 proficiency and L2 anxiety in L2 communication compared to the L2 description. It highlights the role of social skills in L2 communication. As stated above, L2 proficiency has been an essential key factor in examining neural processes in bilinguals, but this was the first study that focused on L2 anxiety to explore communication. It may produce significant results if set as a variable to address emotional processing in the bilingual brain.

All studies except one (Hsu et al., 2015 ) utilized isolated and decontextualized words to examine emotional processing in the brain. This major limitation calls for the dire need for future work to draw a comprehensive and detailed picture of brain functioning in bilinguals and language coupling processes by simulating the context in the lab. Only positive emotional words were compared with neutral words in all the summarized neuroimaging studies except Vélez-Uribe ( 2018 ). Arousal and emotional word types have been neglected except in the study of Wu and Zhang ( 2019 ), who utilized both positive emotion-label and positive emotion-laden words and concluded that emotion-laden words elicited different brain area activation. It conforms to the results of studies in other psychological paradigms, indicating that emotion-laden words show different physiological signs in emotion cognition. Neuroimaging studies need to examine the phenomenon under discussion by utilizing emotion-laden narratives.

A journey in neuroimaging studies through a microscopic lens revealed the need to read brain images of emotional processing with the theoretical perspectives of neurolinguistics. The vast gap drawn here confirms that affective neurolinguistics needs more attention from bilingualism and neuroscience, integrating their theoretical and methodological considerations to draw more conclusive results. Neuroimaging studies in emotional processing in bilinguals need to adopt the stimuli utilized in other psychological paradigms and broaden their research spectrum, benefiting from the gaps in those paradigms as indicated above. It will help academics and stakeholders design a better curriculum and provide better teaching and learning content, techniques, and environments focused on emotion cognition in L2 to gain native-like command.

Summary and future work recommendations

The most robust results on emotional processing in bilinguals across all three paradigms have been obtained with single words, mainly valanced ones, compared to neutrals, taboo words, and aversive words. However, we argue that emotional processing based on a single word is not convincing since language is not processed merely as a single decontextualized word, registered individually. Words in their co-text, pragmatic contexts, such as intentionality and relevance, social skills, previous experiences, and cultural usage, are hypothesized to produce visible effects in eliciting emotions. Appropriate identification patterns are not acquired by age; attributing affective qualities to verbal stimuli of words and narratives depends on proficiency in the language. All studies compiled in this review had participants with L1 as their dominant language, producing automaticity of emotional processing in L1 instead of L2. Therefore, future research in neurolinguistics focusing on language in context should primarily focus on language dominance rather than L1. It is because the ability to make cognitive judgments, the interplay of individual socialization skills, and language ideologies are the factors underpinning language dominance.

All the psychophysiological, cognitive, and neuroimaging studies reviewed here selected sequential bilinguals as their subjects of inquiry without describing any difference between the performance of simultaneous and sequential bilinguals. Therefore, future research in emotional processing in neurolinguistic bilinguals should focus on this aspect. We hypothesize that L2 may become the dominant language of a sequential bilingual, depending on social and linguistic exposure. Thus, future research should examine questions such as whether sequential bilinguals with L2 dominance outperform simultaneous bilinguals with L2 dominance, whether sequential bilinguals with L1 dominance show any difference from simultaneous bilinguals with dominance in L1 in affective processing, and whether overall language dominance matters in emotional processing, overcoming the differences in simultaneous and sequential bilinguals.

In summary, the studies on emotion-label/emotion-laden words and valenced attributes reviewed above do not describe any underlying processes driving the differences in emotional processing. These processes may be further affected by replacing single-word stimuli with cohesive narratives, configuring them with parallel linguistic processes, simulating the lab’s context, the role of language dominance, and the difference between simultaneous and sequential bilinguals. Working on this broad canvas of multiple pitfalls will help neurolinguistics evolve from infancy to maturity.

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Sharif, H., Mahmood, S. Emotional processing in bilinguals: a systematic review aimed at identifying future trends in neurolinguistics. Humanit Soc Sci Commun 10 , 438 (2023). https://doi.org/10.1057/s41599-023-01926-1

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Cognitive Consequences of Bilingualism and Multilingualism: Cross-Linguistic Influences

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• Michael C. W. Yip   ORCID: orcid.org/0000-0002-9790-334X 1  

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Bilingualism and multilingualism are common in almost all communities worldwide today. Research studies on the psycholinguistics of bilingualism and multilingualism in East Asia region has developed tremendously in the past 20 years. Along with the new methodologies, innovative approaches, and the development of those state-of-the-art technologies (Altarriba and Heredia (eds) in An introduction to bilingualism: principles and processes, Routledge, 2018), a lot of new research findings on this line of research have been reported.

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Yip, M.C.W. Cognitive Consequences of Bilingualism and Multilingualism: Cross-Linguistic Influences. J Psycholinguist Res 50 , 313–316 (2021). https://doi.org/10.1007/s10936-021-09779-y

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SYSTEMATIC REVIEW article

The impact of bilingualism on executive functions in children and adolescents: a systematic review based on the prisma method.

• 1 Dipartimento di Psicologia, Sapienza Università di Roma, Roma, Italy
• 2 Instituto de Estudios Sociales y Humanísticos, Universidad Autónoma de Chile, Santiago de Chile, Chile
• 3 Dipartimento di Psicologia e dei Processi di Sviluppo e Socializzazione, Sapienza Università di Roma, Roma, Italy
• 4 Dipartimento di Psicologia Dinamica e Clinica, Sapienza Università di Roma, Roma, Italy

Approximately half of the world's population is bilingual or multilingual. The bilingual advantage theory claims that the constant need to control both known languages, that are always active in the brain, to use the one suitable for each specific context improves cognitive functions and specifically executive functions. However, some authors do not agree on the bilingual effect, given the controversial results of studies on this topic. This systematic review aims to summarize the results of studies on the relationship between bilingualism and executive functions. The review was conducted according to PRISMA-statement through searches in the scientific database PsychINFO, PsycARTICLES, MEDLINE, and PUBMED. Studies included in this review had at least one bilingual and monolingual group, participants aged between 5 and 17 years, and at least one executive function measure. Studies on second language learners, multilingual people, and the clinical population were excluded. Fifty-three studies were included in the systematic review. Evidence supporting the bilingual effect seems to appear when assessing inhibition and cognitive flexibility, but to disappear when working memory is considered. The inconsistent results of the studies do not allow drawing definite conclusions on the bilingual effect. Further studies are needed; they should consider the role of some modulators (e.g., language history and context, methodological differences) on the observed results.

Introduction

Approximately half of the world population is bilingual or multilingual ( Ansaldo et al., 2008 ). In 2016, 64.6% of the European population aged 25–64 declared they knew one or more foreign languages. When considering only 25–34-year-olds, this percentage rises to 73.3% ( Eurostat, 2016 ). Moreover, the number of immigrant children worldwide who do not speak the majority language of their place of residence has increased ( OECD, 2010 ). Despite that, there is no single definition of bilingualism. Among the definitions of bilinguals, the most inclusive is the one by Edwards (2004) , who states that “everyone is bilingual” because there are no (adult) people in the world who do not know at least some words in a language different from their native language. According to other definitions ( Abdelgafar and Moawad, 2015 ), only people who know two languages with a level of competence equal to that of a native speaker can be considered bilingual. The more common definition is “someone who can function in both languages in conversational interaction” ( Wei, 2020 ). The age of acquisition (AoA) of the second language is another factor that characterizes bilinguals, allowing to classify them in simultaneous bilinguals, when both languages are learned during infancy, and sequential bilinguals, when they are exposed to the second language after infancy, usually at school entry ( Gross et al., 2014 ). Other authors also include learning a second language as they define bilinguals who can correctly produce sentences in a language other than their native language ( Hakuta, 1986 ). The absence of standard guidelines has led to heterogeneity in the populations considered by studies on bilingualism, often including people with different language histories and competencies (for a list of terms used to describe bilinguals, see Wei, 2020 ).

The first studies on bilingualism date back to the early 1900s. Initially, several researchers supported the hypothesis that bilingual children had lower mental abilities than monolinguals because the knowledge of several languages would generate a mental confusion with deleterious consequences on every cognitive aspect ( Hakuta, 1986 ). Peal and Lambert (1962) were the first to contradict this negative view about the bilingualism effect. Because of the positive results of subsequent studies, a new theory advanced the view of bilingualism advantage. The positive effect of bilingualism would depend on the constant need to control both known languages to use the one suitable for each specific context, and this process would generate more significant neurological development ( Bialystok, 1999 , 2001 ). According to the Joint Activation Model of Green (1998) , both languages would always be active in the brain of a bilingual person regardless of the language used at the given moment; for this reason, it would be necessary to use a general suppression mechanism to inhibit the activation of the non-target language. Green and Abutalebi (2013) highlighted the importance of the context in which language exchanges take place. They proposed the Adaptive control hypothesis and identified three possible contexts of interaction: single-language, dual-language, and dense code-switching contexts. Depending on the communicative context in which bilinguals are immersed, the languages may cooperate or compete. For this reason, each context is characterized by a different use of processes that are the basis of communication. The use of multiple languages would seem to modify both the language network and the control network ( Green and Kroll, 2019 ).

Some of the cognitive functions that would seem to benefit from the knowledge of several languages are the metalinguistic and metacognitive awareness, the ability to represent abstract and symbolic concepts (for a review see Adesope et al., 2010 ), and specifically, the bilingualism should improve the executive functioning.

According to the model of Miyake et al. (2000) , executive functions refer to cognitive flexibility (e.g., the ability to switch between tasks), inhibition (e.g., the ability to suppress dominant responses) and monitoring (e.g., the ability to update information in the working memory).

According to Bialystok (2011) , bilinguals have an advantage in executive functions because they would continuously train them to carry on a conversation that must be based on the context and require constant access to the information contained in the working memory. Furthermore, it is necessary to select the appropriate language for the specific communicative situation (inhibiting the other language) and to monitor what happens during the interaction (cognitive flexibility).

It has been shown that executive functions can be improved through training ( Karbach and Kray, 2009 ; Moreno et al., 2011 ). The study of the “bilingual advantage” is not only one of the main topics discussed in bilingualism research, but it is also the most controversial one. After the publication of positive evidence on the bilingual advantage, the difficulty in replicating previous results and the publication of several studies with null findings led to questioning this theory. Recently, the use of the term “bilingual advantage” has been questioned because its presence or absence could depend on the interpretation or perspective of the observer. Leivada et al. (2020) suggested adopting the more neutral term “bilingual effect.” Paap et al. (2015) stated that “bilingual advantages in executive functioning either do not exist or are restricted to very specific and undetermined circumstances” and pointed out that 80% of the tests carried out after 2011 failed to obtain results in support of the bilingual effect.

Paap et al. (2015) hypothesized that the results of previous studies on this topic could be due to the lack of control of several external factors, the experimental tasks chosen to evaluate it, and the limited number of participants included in the studies. Other factors that play a role in determining these results are socioeconomic status (SES) and the participants' cultural and linguistic background. For example, the tests used for the assessment of bilinguals are usually the same as those used and validated for monolinguals. The condition of bilingualism can influence the performance in various domains (positively or negatively). In that case, it follows that some of the standardized tests currently in use are not always suitable for the assessment of bilinguals and that the normative data currently available do not reflect the real abilities of bilinguals (e.g., assessment of linguistic abilities in bilingually developing children, see for example Core et al., 2013 ; Bailey et al., 2020 ). One of the characteristics of the experimental tasks that seem to influence the performance of people who know several languages is the use of verbal stimuli ( Duñabeitia et al., 2014 ).

Many studies have shown that bilinguals perform more poorly than monolinguals on linguistic tasks (e.g., Bialystok, 2009a ), have a smaller vocabulary than monolinguals ( Bialystok et al., 2010 ) and produce fewer words in verbal fluency tasks ( Zeng et al., 2019 ). These findings could be due to the lower use and the specificity of each language. The characteristics of the two languages could depend on how they were learned and used ( Blom et al., 2014 ). When the vocabulary size is assessed considering both known languages, this deficit disappears, and bilinguals show a more extensive vocabulary size than monolinguals ( Bialystok, 2009b ).

The use of verbal stimuli implies the activation in the brain of bilinguals of two different linguistic forms per stimulus and difficulty in coding when the presented word is known in the other language than the one used for the assessment. Other factors related to language skills seem to affect the performance of bilinguals. In tasks using verbal stimuli, both the similarity of the languages known and the native language would seem to affect the results. Unfortunately, however, for many of the aspects of the linguistic experience, there is still no agreed conclusion between the different researchers. For instance, what is the degree of balance that must exist between the two languages to generate the bilingual effect? Some studies argue that the bilingual effect emerges when bilinguals have complete mastery of the two languages ( Filippi et al., 2015 ). Therefore, the advantage should be due to the higher cognitive effort needed to reduce interference between the two languages ( Blom et al., 2014 ); other researches asserted that the potential cognitive effects are proportionate to the degree of balance between languages ( Carlson and Meltzoff, 2008 ; Ladas et al., 2015 ).

Other authors argue that the degree of control that bilinguals must apply is higher when they are not equally fluent in the two languages; therefore, the absence of significant differences in the studies could be due to the inclusion of participants with a balanced competence in the two languages for whom the process of switching has become automatic ( Gathercole et al., 2014 ). A factor that does not seem to affect the degree of advantage in executive functioning is the knowledge of more than two languages ( Poarch and van Hell, 2012 ; Poarch and Bialystok, 2015 ). The type of language known and the degree of similarity between them is also an aspect to be considered. Several authors have pointed out that the similarity between languages is a decisive factor in determining the bilingual effect (e.g., Bialystok et al., 2003 ), while phonological and orthographic differences can negatively affect performance, generating interference during the evaluation ( Jalali-Moghadam and Kormi-Nouri, 2015 ).

There are also specific characteristics of the experimental tasks that seem to affect the performance of bilinguals. Several studies agree that the bilingual effect would emerge in more complex experimental tasks where there is a higher demand for control (e.g., Engel de Abreu et al., 2012 ; Barac et al., 2016 ). Further, the tendency to use experimental tasks that empirically isolate executive functions seems to contribute to unclear results ( Barac et al., 2016 ). Most experimental tasks inevitably engage other cognitive processes while evaluating a specific domain (task impurity problem; Miyake and Friedman, 2012 ). Isolating the executive functions experimentally also does not allow the evaluation of real conditions since, in daily life, rarely exist tasks involving a single component of cognitive functions. Another aspect to consider is test-retest reliability. Several experimental tasks used to evaluate executive functions are characterized by low test-retest reliability, and this factor should lead to a more cautious interpretation ( Karalunas et al., 2016 ; Leivada et al., 2020 ). Additionally, bilingualism seems to have a more significant impact when it is required to coordinate multiple functions simultaneously ( Bialystok, 2011 ).

Other factors, such as socioeconomic status, cultural aspects, or immigrant status, would seem to have a role in determining the results achieved by bilingual participants. In several American countries, the condition of bilingualism is a consequence of migratory phenomena, and it is associated with low socioeconomic status ( Calvo and Bialystok, 2014 ). In other countries, for example, in Arab Countries, bilinguals usually belong to a high social class and often learn more than one language because they receive a bilingual school education ( Abdelgafar and Moawad, 2015 ). It is known that low socioeconomic status leads to lower cognitive functioning ( Rosen et al., 2019 ). Given the high frequency of low socioeconomic status and reduced vocabulary in bilinguals, several authors have indicated the importance of analyzing these aspects and monitoring the effect of these variables statistically if a difference between groups is present. Although many authors considered that statistical control of these variables is the correct procedure (e.g., Carlson and Meltzoff, 2008 ; Blom et al., 2014 ), others believe that these conditions are a specific characteristic of the population of interest ( Buac et al., 2016 ).

This systematic review aims to summarize the findings of studies investigating the relationship between bilingualism and executive functions in children and adolescents. It will be verified whether bilingualism affects one or more specific executive functions. Studies that have used the same task will be compared, highlighting any changes that have been made to the experimental tasks that could influence the results. The studies will be analyzed to identify any factors that may be involved in determining the outcomes. We excluded studies with older adult participants from this systematic review, although they provide the strongest evidence for a bilingual effect ( Antón et al., 2014 ). As Baum and Titone (2014) suggested, older adults experienced a historical and cultural moment in which attitudes toward bilingualism were very different from those of today. This factor could have affected the use of languages at various times in their lives. Moreover, studies with adults would imply the need to consider many other factors (e.g., drug treatment). We believe it is necessary to conduct a systematic review focusing only on this population, considering its specific characteristics.

The review process was conducted according to the PRISMA Statement ( Liberati et al., 2009 ; Moher et al., 2009 ). The PRISMA Statement consists of a 27-item checklist and a four-phase flow diagram and helps authors improve systematic review reporting. This review was registered as PROSPERO CRD42019127965.

Research Strategies

A systematic search of the international literature was conducted in the following electronic databases by selecting articles published in peer-review journals: PsycINFO, PsycARTICLES, MEDLINE, and PubMed. The last research was conducted on 15 April 2020. Restrictions were made limiting the research to academic publications in English, Italian, and Spanish. No restriction of age, gender, or ethnicity was made. The search strategy used Boolean combinations of the following keywords: “bilingual * ,” “second language user,” “executive function * ,” “cognitive flexibility,” “shifting,” “task switching,” “updating,” “working memory,” “inhibition,” and “cognitive inhibition.” Reference lists of the selected articles were screened. A total of 3,785 articles were obtained from the search procedure. Mendeley reference manager software was used for removing duplicates. The first screening was made by reading the title and abstract. The full text of the selected studies was read.

Eligibility Criteria

The studies that respected the following characteristics were included: the presence of at least one bilingual group and one monolingual group, at least one executive function measured, age of participants between 5 and 17 years. Studies on preschool-age children were excluded because the EFs and underlying neural areas are immature and still developing ( Diamond, 2013 ). The age limit has been set at 17 years because, during middle adolescence, the peak of executive functions is reached ( Anderson, 2002 ). Studies on bimodal bilingual, second language learners, and trilingual or multilingual people were excluded. Studies on clinical populations were excluded. All the selected studies were screened to assess the risk of bias using Standard quality assessment criteria for evaluating primary research papers from various fields ( Kmet et al., 2011 ). The studies were included if they reached a score above 70%.

Data Collection

According to the PICOS approach ( Liberati et al., 2009 ), the following information has been extracted from the selected studies: author(s) and year of publication, country, characteristics of participants (age, percentage of females, spoken languages, use of languages, socioeconomic status), criteria used for selecting bilingual participants, the experimental paradigm used, results of the studies. These data are summarized in Tables 1 , 2 .

Table 1 . Main characteristics of the studies included.

Table 2 . Bilingual participants' characteristics in the selected studies.

Selection of Studies

The flowchart ( Figure 1 ) shows the number of studies identified from the databases and the other sources, the number of studies examined by the authors, and assessed for eligibility. The reasons for exclusion are reported.

Figure 1 . Studies selection flow diagram (PRISMA flow chart).

Results of the Selected Studies

Of the 53 studies identified, 24 were conducted in Europe, 10 in America, two in Asia, one in Africa, one in Australia, and 14 did not report the country. Bialystok and Viswanathan (2009) included participants from two different continents (America and Asia).

Twenty-seven studies included bilingual participants who knew a specific language pair while in 23 studies, bilinguals spoke a common language plus another language. Bialystok and Viswanathan (2009) included two groups of bilingual participants, one speaking a specific language pair, the other speaking different languages. Two studies ( Barac and Bialystok, 2012 ; Blom et al., 2017 ) included distinct groups of bilingual participants with different linguistic backgrounds to check if the type of language known, influenced the results.

In most studies, information on the participants' linguistic background was collected through interviews or questionnaires made to their caregivers. In two studies, the information was collected by directly interviewing the participants ( Jalali-Moghadam and Kormi-Nouri, 2015 ; Raudszus et al., 2018 ). The analyzed studies reported different definitions of bilingualism; some of these definitions are based on the assessment of the competences in the two languages; others are founded on the age of acquisition of the two languages. Twenty-five studies reported information on the time of acquisition of the second language (e.g., type of bilingualism, the age range in which the languages were learned), but only 12 studies indicated the age of acquisition. Most of the studies did not indicate the language context in which the children were immersed, and only eight studies defined the language used at home by parents and children. Forty-five studies assessed the participants' language skills using both tests and self-report questionnaires or interviews. In twenty-four studies were assessed both languages known by the bilingual participants. In three studies ( Escobar et al., 2018 ; Dick et al., 2019 ; Zeng et al., 2019 ), objective assessments and self-report questionnaires were used. The use of both tools allows investigating both language proficiency (tests) and language use (self-report), two aspects that can contribute to a better description of the bilingual experience ( Luk and Bialystok, 2013 ). Twenty-four studies reported a reduced vocabulary for bilinguals compared to monolinguals considering only the groups' common language. In three studies, no assessment of the participants' language skills was conducted. Many of the studies provided information on socioeconomic status, and the most used as an indicator of SES the educational level of parents. In nine studies, the group of bilinguals had a lower socioeconomic status than monolinguals. In Veenstra et al. (2018) , the bilinguals had a higher socioeconomic status than monolinguals. Nine studies did not report information on the SES (see Table 2 ).

Bilingualism and Attention (n = 11)

Eleven studies examined the effect of bilingualism on attention. Three studies ( Engel de Abreu et al., 2012 , 2014 ; Blom et al., 2017 ) used the Sky Search task of the Test of Everyday Attention for Children ( Manly et al., 1999 ) to assess selective attention. Participants were asked to identify pairs of identical pictures on a sheet of paper while ignoring the presence of distracting stimuli. In all studies, bilingual participants took less time to solve the task compared to monolinguals.

Calvo and Bialystok (2014) used the Pair Cancellation Subtest of the Woodcock-Johnson Tests of Cognitive Abilities-III ( Woodcock et al., 2001 ) to assess non-verbal visual attention and the cancellation subtest of Wechsler Intelligence Scale for Children-Fourth Edition (WISC-IV; Wechsler, 2003 ) to assess verbal-visual attention. In the task with verbal stimuli, bilinguals performed significantly worse than monolinguals, while in the task with non-verbal stimuli, no differences emerged between the two groups.

Seven studies ( Carlson and Meltzoff, 2008 ; Kapa and Colombo, 2013 ; Antón et al., 2014 ; Ladas et al., 2015 ; Barac et al., 2016 ; Yang and Yang, 2016 ; Veenstra et al., 2018 ) used the child-friendly version of the Attentional Network Task proposed by Rueda et al. (2004) to assess the three attentional networks (alerting, orienting, and executive control).

In Ladas et al. (2015) , the participants also carried out the Attentional Network Task for Interaction ( Callejas et al., 2004 ). Four studies ( Carlson and Meltzoff, 2008 ; Antón et al., 2014 ; Ladas et al., 2015 ; Veenstra et al., 2018 ) found no significant difference in performance between monolinguals and bilinguals. In Yang and Yang (2016) , bilingual children were globally faster and more accurate than monolingual children. No differences were found in the three attention indexes (alerting, orienting, and executive control).

The authors also calculated the global inverse efficiency scores by dividing the mean reaction times by accuracy percentage. This index indicated an advantage for the bilingual group over the monolingual group. In Barac et al. (2016) , no significant differences in RTs or attentional indexes emerged between bilinguals and monolinguals. In Kapa and Colombo (2013) , both reaction times and the percentage of accuracy were analyzed by using age and vocabulary as covariates. For reaction times, the early bilingual group (i.e., children who learned both languages before the age of three) was significantly faster than the monolingual group. At the same time, no significant differences emerged between the later bilingual group (i.e., children who learned Spanish before the age of three and English after three) and the monolingual group. The two bilingual groups did not differ between them. No significant differences were found between the three groups in the percentage of accuracy and the attentional indexes.

Bilingualism and Visual Working Memory (n = 17)

Four studies ( Bialystok and Viswanathan, 2009 ; Gangopadhyay et al., 2016 ; Park et al., 2018 ; Veenstra et al., 2018 ) used the Corsi blocks task to assess visuospatial working memory. No significant differences emerged between the performance of monolinguals and bilinguals. Four studies ( Engel de Abreu et al., 2012 , 2014 ; Blom et al., 2014 , 2017 ) used a modified version of this task, the Dot Matrix Task, and again no significant differences between the two groups' performance were found. In the study of Blom et al. (2014) to verify whether age, socioeconomic status, defined as the average education level of both parents, and vocabulary size, influenced the results, these variables were used as covariates in the statistical analysis and participants were divided into two age groups. Results showed that bilinguals at 6 years had a better performance than monolinguals. Two studies ( Morales et al., 2013 ; Calvo and Bialystok, 2014 ) used a child-friendly version of the Corsi blocks task, the Frog Matrices Task. In Calvo and Bialystok (2014) , bilinguals were more accurate than monolinguals. In Morales et al. (2013) , bilinguals showed a higher proportion score (calculated as the number of remembered elements divided by the total number of elements) than monolinguals in the sequential condition. In the less demanding condition, i.e., the simultaneous condition, no significant differences emerged between the two groups.

Three studies ( Gangopadhyay et al., 2016 ; Arizmendi et al., 2018 ; Janus and Bialystok, 2018 ) used the N-back task to assess non-verbal working memory. In Gangopadhyay et al. (2016) , no significant differences were found between bilinguals and monolinguals. Arizmendi's et al. (2018) study used two N-back tasks (i.e., N-back Auditory task and N-back Visual task), and monolinguals solved the tasks more efficiently than bilinguals. In Janus and Bialystok (2018) , who used a modified version with emotional stimuli, bilinguals were more accurate than monolinguals when they had to indicate that the target was the same as in the previous trial (target trial) than when it was not (non-target trial). Furthermore, bilinguals had slower reaction times than monolinguals when a target trial (2-back condition) or a no target trial was presented (1-back and 2-back conditions).

Three studies ( Engel de Abreu et al., 2012 , 2014 ; Blom et al., 2014 ) used the Odd-One-Out task. No significant differences were found in any of the studies.

Jalali-Moghadam and Kormi-Nouri (2015) used the Concentration task ( Schumann-Hengseler, 1996 ) and the Tower of Hanoi ( Welsh, 1991 ) and no significant differences emerged between bilingual and monolingual participants.

Morales et al. (2013) used the Picture Task. Bilinguals solved the task more efficiently with faster reaction times in all conditions. Bilinguals had the same accuracy score in congruent and incongruent trials, while monolinguals were negatively affected by the incongruent condition.

Two studies ( Bialystok, 1999 ; Carlson and Meltzoff, 2008 ) used the Visually Cued Recall task ( Zelazo et al., 1997 ) and did not find differences between bilinguals and monolinguals.

Bonifacci et al. (2011) used two experimental tasks to assess visual working memory in which participants were required to indicate whether a target stimulus appeared within a string of stimuli. Numerical and unknown alphabetical symbols were used as stimuli. There were no significant differences between the performance of the two groups. Cottini et al. (2015) used the Color-Shape binding task (adapted from Allen et al., 2006 ), bilinguals were more accurate than monolinguals only in the shape condition, while there were no differences in the color condition and the combination of the two conditions. Furthermore, bilinguals presented more false alarms than monolinguals only in the combination condition.

Bilingualism and Verbal Working Memory (n = 21)

Four studies used the listening recall task to assess working memory. In Leikin and Tovli (2014) , participants had to complete sentences with the missing word, and then they have to recall the complete list of words used ( Shani et al., 2005 ). In two studies ( Buac et al., 2016 ; Schröter and Schroeder, 2017 ), participants had to judge whether the sentences were true or false, and then remember the last word ( Daneman and Carpenter, 1980 ). In Bosman and Janssen (2017) , a modified version of this task was adopted in which participants were required to remember the first word because, in the participants' language, the last word of the sentence was always a verb. Within these studies, only Leikin and Tovli (2014) found a significant difference between groups, with bilinguals who named more correct words than monolinguals. The number of the correct sequences (i.e., the number of correct orders of the words) was the same in the two groups. In Bosman and Janssen (2017) , bilingual children's performance was worse than that of monolinguals. In two studies ( Buac et al., 2016 ; Schröter and Schroeder, 2017 ), no significant differences emerged.

Bialystok and Feng (2009) used the Proactive Interference Task, and no significant differences in the performance of the two groups were found.

Eighteen studies ( Danahy et al., 2007 ; Bialystok and Feng, 2009 ; Bialystok and Viswanathan, 2009 ; Bialystok, 2010 ; Engel de Abreu, 2011 ; Kapa and Colombo, 2013 ; Blom et al., 2014 , 2017 ; Engel de Abreu et al., 2014 ; Filippi et al., 2015 ; Garraffa et al., 2015 ; Buac et al., 2016 ; Cockcroft, 2016 ; Bosman and Janssen, 2017 ; Raudszus et al., 2018 ; Veenstra et al., 2018 ; Hartanto et al., 2019 ; Jaekel et al., 2019 ) evaluated working memory by using different versions of the digit span task. In 12 studies ( Danahy et al., 2007 ; Bialystok and Feng, 2009 ; Bialystok and Viswanathan, 2009 ; Engel de Abreu, 2011 ; Kapa and Colombo, 2013 ; Engel de Abreu et al., 2014 ; Filippi et al., 2015 ; Garraffa et al., 2015 ; Cockcroft, 2016 ; Blom et al., 2017 ; Raudszus et al., 2018 ; Veenstra et al., 2018 ) no significant differences between the two groups emerged. In three studies, monolinguals remembered a significantly higher number of digits than bilinguals in the forward digit span task ( Buac et al., 2016 ; Bosman and Janssen, 2017 ) and backward digit span ( Jaekel et al., 2019 ). In Bialystok (2010) , which reported three studies involving three different groups of participants, bilinguals' scores were lower than monolinguals' scores only in the third study. In this study, bilingual participants had a smaller vocabulary size when compared to monolinguals. In Blom et al. (2014) , bilinguals scored were higher in both forward and backward digit span. In Hartanto et al. (2019) , which assessed the performance in four different time waves, bilinguals had better performance than monolinguals only in time 4 (mean age bilinguals: 7.13; mean age monolinguals: 7.05).

Three studies ( Engel de Abreu, 2011 ; Garraffa et al., 2015 ; Cockcroft, 2016 ) evaluated short-term verbal memory using the non-word repetition task. In Engel de Abreu (2011) , the monolinguals repeated a significantly higher number of non-word than bilinguals. To verify whether the difference in vocabulary size between participants affected the results, the author repeated the analysis using the receptive vocabulary score as a covariate, and the difference between the two groups disappeared. In the other two studies, there were no significant differences in the performance of the two groups.

Arizmendi et al. (2018) used the number updating task, and no differences emerged between the two groups of participants.

Bilingualism and Inhibition (n = 28)

Two studies ( Bonifacci et al., 2011 ; Barac et al., 2016 ) used the Go/No-Go Task. In Barac et al. (2016) , bilinguals were faster and more accurate than monolinguals. The d' index indicated a better discriminatory capacity in the bilingual group. In Bonifacci et al. (2011) , which used a modified version of the Go/No-Go task, the No-Go condition consisted of an image accompanied by a sound; the two groups were equal on the number of omissions, the percentage of accuracy and the RTs.

Two studies ( Arizmendi et al., 2018 ; Dick et al., 2019 ) used the Stop-Signal task, and no differences between the performances of the two groups emerged.

Nine studies ( Gathercole et al., 2010 ; Duñabeitia et al., 2014 ; Mohades et al., 2014 ; Abdelgafar and Moawad, 2015 ; Jalali-Moghadam and Kormi-Nouri, 2015 ; Schröter and Schroeder, 2017 ; Arizmendi et al., 2018 ; Escobar et al., 2018 ; Nayak et al., 2020 ) assessed cognitive inhibition by using the Stroop task ( Stroop, 1935 ). Two studies ( Abdelgafar and Moawad, 2015 ; Jalali-Moghadam and Kormi-Nouri, 2015 ) used the pencil and paper version of this task and did not find any significant difference in the performance of monolingual or bilingual participants. Two studies ( Duñabeitia et al., 2014 ; Schröter and Schroeder, 2017 ) adopted the computerized version of the task, and no significant differences between the groups occurred. In two studies ( Duñabeitia et al., 2014 ; Mohades et al., 2014 ), a modified version of the task with numerical stimuli was adopted. In this task, children had to report which number was larger, ignoring the physical size of the digits. In Duñabeitia et al. (2014) , no significant differences between the groups were found. In Mohades et al. (2014) , no significant differences between the groups were found for RTs and accuracy, but the bilingual group showed a higher congruency effect. Nayak et al. (2020) used animal stimuli and did not find significant differences between the two groups, even after controlling for age and socioeconomic status. In Gathercole et al. (2010) , monolingual participants solved the classic Stroop task in English while bilinguals carried out the task in both English and Welsh. There were no significant differences among the three groups of bilinguals in both accuracy and reaction times in the Welsh version. Significant differences in accuracy score in the primary school age group emerged in the English version. The comparison among the three bilingual groups showed a lower accuracy in the group exposed at home to Welsh for 80% of the time from birth (OWH). Monolinguals had significantly fewer accuracy scores than those exposed to both Welsh and English at home from birth (WEH). For reaction times, significant differences emerged only in the teens, and monolingual participants responded significantly slower than all bilingual groups. Escobar et al. (2018) used the Day-Night Stroop Task. The experimental task included congruent trials in which participants named the word corresponding to the presented stimulus (e.g., the word day for the sun) and incongruent trials in which they had to pronounce the word opposite to the presented stimulus (e.g., the word day for the moon). No significant differences emerged between the two groups. In Arizmendi et al. (2018) , two modified versions of the Stroop task were used. In both versions, participants had to respond orally. No significant differences emerged between bilinguals and monolinguals.

Nine studies ( Engel de Abreu et al., 2012 , 2014 ; Calvo and Bialystok, 2014 ; Poarch and Bialystok, 2015 ; Blom et al., 2017 ; Ross and Melinger, 2017 ; Park et al., 2018 ; Struys et al., 2018 ; Dick et al., 2019 ) evaluated the interference suppression ability using the Flanker task ( Eriksen and Eriksen, 1974 ). In four studies ( Engel de Abreu et al., 2012 , 2014 ; Poarch and Bialystok, 2015 ; Park et al., 2018 ), bilingual participants had faster RTs. In two studies ( Poarch and Bialystok, 2015 ; Park et al., 2018 ), this advantage emerged in the incongruent condition indicating a better ability to control conflictual information in the bilingual group.

In Blom et al. (2017) , the performance in the Flanker task correlated negatively with the scores in memory tasks, indicating that children with better results in memory tasks had faster reaction times. Moreover, multiple linear regression results have suggested that a more extended vocabulary size is associated with a better ability to perform this experimental task. However, no significant differences between monolinguals and bilinguals emerged. Three studies ( Calvo and Bialystok, 2014 ; Ross and Melinger, 2017 ; Dick et al., 2019 ) showed no significant difference in RTs between bilinguals and monolinguals, but in Calvo and Bialystok (2014) bilinguals reached a higher percentage of accuracy. Struys et al. (2018) analyzed the speed-accuracy trade-off effect (i.e., an increase in accuracy corresponds to an increase in reaction times and vice versa) to verify whether the participants adopted different resolution strategies in the experimental tasks. The results indicated a speed-accuracy trade-off effect in the older bilingual group (mean age: 11.7) but not in the younger bilingual group (mean age: 6.6) or in the monolingual groups. The authors hypothesized that the effect was not present in both groups of bilinguals because they may have adopted different strategies (preferring speed in some cases and accuracy in others). To highlight an advantage in the speed-accuracy trade-off effect, it seems necessary that most participants adopt the same strategy.

Seven studies analyzed the ability to manage conflictual information by using the flanker task in the experimental context of the Attentional Network Test ( Carlson and Meltzoff, 2008 ; Kapa and Colombo, 2013 ; Antón et al., 2014 ; Ladas et al., 2015 ; Barac et al., 2016 ; Yang and Yang, 2016 ; Veenstra et al., 2018 ). In two studies ( Antón et al., 2014 ; Ladas et al., 2015 ), no significant differences in reaction times and the percentage of accuracy between the monolingual and bilingual groups were observed. In the other two studies ( Barac et al., 2016 ; Yang and Yang, 2016 ), no significant differences in reaction times emerged, while bilinguals were more accurate in congruent and incongruent trials than the monolingual group. In three studies ( Carlson and Meltzoff, 2008 ; Kapa and Colombo, 2013 ; Veenstra et al., 2018 ), the Flanker x Group interaction results were not reported.

Seven studies ( Poarch and van Hell, 2012 ; Gathercole et al., 2014 ; Mohades et al., 2014 ; Ross and Melinger, 2017 ; Raudszus et al., 2018 ; Struys et al., 2018 ; Zeng et al., 2019 ) used the Simon Task ( Simon and Wolf, 1963 ). In two studies ( Poarch and van Hell, 2012 ; Raudszus et al., 2018 ), no significant differences emerged between the monolingual and the bilingual groups. Two studies ( Ross and Melinger, 2017 ; Zeng et al., 2019 ) found a lower percentage of errors in the bilingual group than to the monolingual group, while there were no differences between the two groups in reaction times and the Simon effect. In Gathercole et al. (2014) , there were no significant differences between monolinguals and bilinguals in the primary schoolers and teens groups. In the group of 5-year-olds, no difference emerged for the percentage of accuracy. However, the monolinguals were faster than the bilingual group exposed at home to English for 80% of the time from birth (OEH). The OWH bilinguals were faster than the OEH bilinguals. In Mohades et al. (2014) , bilinguals achieved the same performance as monolinguals in reaction times and accuracy, but they showed a greater congruency effect. In Struys et al. (2018) , a speed-accuracy trade-off effect occurred in the two groups of bilinguals but not in monolingual participants.

Three studies ( Bialystok, 2010 ; Cottini et al., 2015 ; Arizmendi et al., 2018 ) assessed inhibition using the Global Local Task ( Andres and Fernandes, 2006 ). In Bialystok (2010) , the Global-Local task was proposed in three different versions. Overall, bilinguals were faster under all conditions than monolinguals. Bilinguals were more accurate than monolinguals in the global condition while in the local condition, there was no difference between the two groups. Moreover, the mixing costs (the difference between trials alone and trials in mixed condition) were smaller for bilinguals than for monolinguals. In Cottini et al. (2015) , bilinguals were more accurate than monolinguals in incongruent and neutral trials, and the total effect of interference was higher in the monolingual group. In this study, bilinguals were more accurate than monolinguals in the local incongruent trials, while monolinguals performed significantly better than bilinguals in the global incongruent trials. In Arizmendi et al. (2018) , no significant differences were found between monolingual and bilingual participants.

Two studies ( Carlson and Meltzoff, 2008 ; Barac et al., 2016 ) used a delay gratification task to assess the ability to inhibit dominant responses. In both studies, no significant differences were found between the monolingual and bilingual participants.

Two studies ( Garraffa et al., 2015 ; Schröter and Schroeder, 2017 ) used the Opposite World Task from the Test of Everyday Attention for Children ( Manly et al., 2001 ) in which it is required to inhibit a dominant verbal response. In Garraffa et al. (2015) , bilinguals were slower than monolinguals, while in Schröter and Schroeder (2017) , no significant difference between the two groups emerged.

Bilingualism and Shifting (n = 12)

Two studies ( Barac and Bialystok, 2012 ; Veenstra et al., 2018 ) used the Color-Shape task switching. In Barac and Bialystok (2012) , bilinguals were faster and had lower global costs than monolinguals. In Veenstra et al. (2018) , which used a composite inhibition score, considering the ANT interference effect, no significant differences emerged between bilinguals and monolinguals. Arizmendi et al. (2018) used a modified version of the Color-Shape task, the Pirate Sorting task, and did not find significant differences between the two groups.

Six studies ( Bialystok, 1999 ; Carlson and Meltzoff, 2008 ; Garraffa et al., 2015 ; Escobar et al., 2018 ; Park et al., 2018 ; Hartanto et al., 2019 ) used different versions of the Dimensional Change Card Sort Task (e.g., Zelazo et al., 1996 ). In four studies ( Bialystok, 1999 ; Carlson and Meltzoff, 2008 ; Garraffa et al., 2015 ; Hartanto et al., 2019 ), the bilingual group gave more correct responses than the monolingual group. In Park et al. (2018) , bilinguals showed lower mixing costs (the difference between trials in the pre-shift condition and non-switch trials in the mixed condition) compared to monolinguals, while no significant difference emerged between the two groups in the switching costs (the difference between non-switch and switch trials in the mixed condition) and shifting costs (the difference between the pre-shift and the post-shift condition). Escobar et al. (2018) found no differences between the two groups.

Gathercole et al. (2014) used a modified card task. In the teen group, the OWH bilingual group was more accurate than the monolinguals and WEH bilinguals. Monolinguals were faster in the group of 5 years old, whereas bilinguals were faster in the group of teenagers.

Ross and Melinger (2017) used a modified version of the Wisconsin Card Sorting Test, the Berg Card Sorting Test ( Piper et al., 2012 ) and did not find differences between the two groups in perseverative errors, reaction times or the number of trials needed to complete a category. However, bilinguals made more total errors than monolinguals.

Gathercole et al. (2010) used the Tapping Task. Three groups of bilinguals who used different languages at home were included in the study. In the primary age group, the OWH and OEH groups showed better performance in the match condition (i.e., emulation of the experimenter's action) and the switch condition (i.e., to do actions contrary to those of the experimenter). In the teen group, the OWH and WEH groups showed an advantage over the monolingual group.

Bilingualism and Multiple Executive Functions (n = 10)

This section examines the results of experimental tasks that evaluated different executive functions at the same time.

Three studies ( Bialystok and Viswanathan, 2009 ; Bialystok, 2010 ; Abdelgafar and Moawad, 2015 ) used the Trail Making Test, a neuropsychological test that allows evaluating visual attention and switching ability. In all studies, bilinguals completed part A faster than monolinguals. In two studies ( Bialystok and Viswanathan, 2009 ; Bialystok, 2010 ), bilinguals solved part B faster.

Five studies ( Bialystok, 2010 ; Abdelgafar and Moawad, 2015 ; Friesen et al., 2015 ; Escobar et al., 2018 ; Zeng et al., 2019 ) used the verbal fluency task. Verbal fluencies require linguistic ability and executive control during lexical access. In the semantic version of this task, the number of possible responses is higher, requiring a high degree of executive control. This result is due to the need to inhibit spontaneous associations not inherent to the criterion and to comply with the restrictions such as the morphological ones ( Friesen et al., 2015 ). In Abdelgafar and Moawad (2015) , semantic fluency was considered an indicator of inhibition ability while in Bialystok (2010) , categorical fluency was considered a verbal productivity indicator. In both studies, no significant differences between the two groups emerged. Conversely, in the other two studies ( Escobar et al., 2018 ; Zeng et al., 2019 ), bilinguals produced more words than monolinguals in letter fluency tasks. In Escobar et al. (2018) , bilinguals produced more words even in the semantic fluency task. In Friesen et al. (2015) , the authors argue that for the performance of the task, it is necessary to involve different components of the executive functions. In terms of categorical fluency, 10-year-old bilingual children produced fewer words than monolinguals. There was no difference in semantic fluency. For the 7-year-old group, there was no difference in both types of verbal fluency between the two groups. However, bilingual children had a higher mean subsequent-response latency, that is, the time in which half of the responses were produced. This index could indicate a difficulty for bilinguals in the lexical access due to the interference produced by the two languages known.

Bialystok and Viswanathan (2009) used the Face Task ( Bialystok et al., 2006 ) to evaluate simultaneously three components of executive functions, i.e., response suppression, inhibitory control, and cognitive flexibility. No significant differences in the performance of the three groups (two bilingual and one monolingual groups) were found considering both response suppression and accuracy. Monolinguals had higher inhibitory and switching costs than bilinguals. The two bilingual groups evaluated in this study did not differ.

Bialystok (2011) used the Dual modality classification task, an experimental task in which stimuli can be visual and auditory. In the single-modality condition, no significant differences in the performance of the two groups emerged. In the dual-modality condition, bilinguals had a higher accuracy score.

Krizman et al. (2016) used the Integrated Visual and Auditory Continuous Performance Test. Participants were required to respond or inhibit the response depending on the specific auditory or visual stimulus presented. Bilinguals performed better than monolinguals. Furthermore, low-SES bilinguals performed better than low-SES monolinguals and at the same level as participants with high SES.

Carlson and Meltzoff (2008) used a modified version of the Kansas Reflectory/Impulsivity Scale (KRISP; Wright, 1971 ), Statue ( Korkman et al., 1998 ), Simon says ( Strommen, 1973 ), and the Gift Delay. These tasks require to suppress motor action during a delay. No significant differences emerged between the bilingual and monolingual groups.

Jaekel et al. (2019) used the Hearts and Flowers task. No significant differences emerged between the bilingual and monolingual groups.

Bilingualism is the knowledge of two languages. Given the absence of a single definition, it is possible to consider bilinguals with a different degrees of proficiency in the languages they know or who have learned languages in different contexts, such as school or home, or different periods of their lives. According to the Joint Activation Model of Green (1998) , bilingualism involves the activation of both languages in the brain, even when only one language is used. This condition seems to have a positive effect on several cognitive functions, including executive functions ( Bialystok et al., 2012 ). After the publication of positive evidence on the bilingual effect, this hypothesis was questioned, given the difficulty in replicating the previous results. This difficulty seems to be due to particular circumstances in which different factors (e.g., age of participants, socioeconomic status, experimental tasks) are involved (i.e., Paap et al., 2015 ).

The current systematic review summarizes the results of 53 studies published between 1999 and 2020 that investigated the effect of bilingualism on executive functions. Analyzing the selected studies, it emerged that the participants had very different characteristics and wide variability in the sample size, ranging from a minimum of 12 participants ( Carlson and Meltzoff, 2008 ) to a maximum of 1740 ( Dick et al., 2019 ). Furthermore, the studies adopted various tasks for the assessment of executive functions. These methodological differences could explain the mixed results found, making it difficult to draw definitive conclusions about the existence of the bilingual effect.

Evidence supporting the existence of the bilingual effect appears when inhibitory control and cognitive flexibility are assessed. In particular, the Sky Search task, the Flanker task, the Dimensional Change Card Sort task, and the Trail Making Test seem to indicate the existence of a bilingual effect. A deeper analysis of the characteristics of the studies included reveals several differences that should lead to a cautious interpretation of the results. The great variability of the experimental tasks becomes evident when considering the studies that used the Stroop task. In particular, the nine studies adopted six different versions of the task. Six studies used different versions of the task with verbal stimuli (i.e., pencil-paper version; computerized version; oral responses version), and found no significant differences between different groups. Two studies used two different versions with non-verbal stimuli, and no significant differences emerged between monolinguals and bilinguals. Two studies used the numerical version, and mixed results were found. However, determining the degree of incidence of the type of stimulus is not possible since no study included both verbal and non-verbal versions of the task. Furthermore, it is not possible to exclude the incidence of the linguistic aspect in the numerical version of the task. As pointed out by Duñabeitia et al. (2014) , it is possible that the linguistic representations of the numbers in the two known languages were active in bilingual brains, and the same may have happened in the non-verbal version since stimuli were used that can be easily verbalized.

Different versions of the task were included in the studies that adopted the Flanker task. The most variable feature was the type of stimulus used (i.e., fish; chevron). Mixed results also emerged in three studies where the same version of the Flanker task was used. Two studies ( Engel de Abreu et al., 2012 , 2014 ) confirmed the bilingual effect, while in Blom et al. (2017) no significant differences emerged. It can be hypothesized that the mixed results may be caused by differences in the participants' linguistic and cultural backgrounds. In two studies ( Engel de Abreu et al., 2012 , 2014 ) bilingual participants were recruited in the Grand Duchy of Luxembourg, a trilingual country with a trilingual education system where children start formal education in the first language at age 4, are exposed to the second language at age six and to the third language at age 7. As the participants in the studies were, on average, eight years old, the bilingual participants included participants that could be considered “trilingual.” In Blom et al. (2017) , three groups of bilingual participants who knew three different language pairs were included. The monolinguals' characteristics may also have influenced the results since, in two studies ( Engel de Abreu et al., 2012 , 2014 ), they were recruited in a different country than the bilinguals. It cannot be excluded that cultural aspects influenced the results.

Most studies that used ANT to evaluate attentive networks did not reveal significant differences between the monolingual and bilingual groups. Again, different factors may have influenced the results. Some authors (e.g., Mullane et al., 2016 ; Lewis et al., 2018 ) highlighted that the child version of the ANT could generate a lower interference effect than the adult version despite the fact that increasing the level of motivation of children to perform the experimental task. When children are evaluated with the adult version, developmental differences emerge that are not visible with the child version. Future studies may adopt the adult version for the assessment of attention in bilinguals. In Yang and Yang (2016) , which found faster reaction times and better accuracy in bilinguals, bilingual participants' cultural. and linguistic background may have influenced the results. Bilingual participants knew a language pair composed of two languages belonging to two different language families, characterized by significant orthographic differences (i.e., Korean-English). This factor seems to have a positive effect on visuospatial abilities ( Yang and Yang, 2016 ). Furthermore, belonging to certain cultures (e.g., Chinese culture) seems to positively influence the development of executive functions ( Carlson and Meltzoff, 2008 ). Also, in Kapa and Colombo (2013) , the bilingual participants' characteristics seem to have a role in the differences that emerged. In the study, the early bilinguals showed better attentive abilities than the monolinguals, but this advantage did not characterize the late bilinguals.

Even in the studies that evaluated the shifting ability with DCCS, some conflicting results emerged. In Park et al. (2018) , significant differences in reaction times emerged between the two groups of participants in the most demanding condition. Other studies using this task confirmed a bilingualism effect. However, it is important to note that in almost all the other studies only the participants' accuracy was assessed. The study of Park et al. (2018) would indicate that the task is too simple for the age considered: the participants included in this study were older compared to the other studies. In Escobar et al. (2018) , the bilinguals had faster reaction times than the monolinguals, but this difference was not significant. The small number of participants (i.e., 17 bilinguals and 17 monolinguals) may have reduced the statistical power of the results.

Another task that showed mixed results is the verbal fluency task. Once again, it is important to highlight that the studies included adopted different versions of this task. Most of the studies that assessed executive functions using category fluency required the participants to name words belonging to the “animals” category. Friesen et al. (2015) used the category “clothing items.” This factor seems to have influenced the results since only in Friesen et al. (2015) did the monolingual group outperformed the bilinguals, whereas, in the other studies, there were no significant differences between the two groups or better performance in the bilinguals. Regarding the letter fluency, several methodological differences emerged. The studies adopted different letters, modalities of administration of the task (oral vs. written production), duration of the test (5 min vs. 1 min), or modalities of calculation of the final score (inclusion or exclusion of incorrect words). Concerning verbal and visual working memory, the evidence for better performance of the bilingual group is limited. In some studies, bilingual participants presented lower performance than monolinguals in the verbal working memory. This result would seem to be mediated by the linguistic abilities of the participants: in Bialystok (2010) , bilinguals showed worse performance than monolinguals only when bilinguals showed a reduced vocabulary size than monolinguals.

Ladas et al. (2015) suggested that, in experimental tasks using verbal stimuli, the absence of a significant result could be interpreted as a bilingual advantage because it is well-known that the vocabulary size of bilinguals, if it is calculated considering only one language, is reduced when compared to that of monolinguals. For example, in Blom et al. (2014) , when the difference in vocabulary size was statistically controlled, a bilingual effect emerged in both the Dot Matrix task and the Digit Backward Recall. However, the absence of significant differences in the performance of bilinguals and monolinguals also emerges in non-verbal tasks, and sometimes even studies using the same experimental task did not observe the same results. These findings suggest that other factors, such as the characteristics of the experimental tasks and the participants, influence the results. The wide variety of tests used for assessing executive functions, which are frequently modified by research groups, makes it difficult to compare the results directly. In several cases, a specific test is used in a single study, or when more than one experimental task is used, the tests chosen had low convergent validity. As suggested by Paap et al. (2015) , each study should include a minimum of two tasks to evaluate each executive function. This methodological choice would make it possible to confirm that controlling that the results are not due to task-specific characteristics. Another point to clarify is whether the bilingual effect only emerges when the task requires a specific degree of complexity or the coordination of several executive functions. In Barac et al. (2016) , which included tasks of increasing difficulty, no differences were observed in the easier task (gift delay), while bilinguals showed an advantage in the more complex tasks (Flanker task and Go/No-Go task). Conversely, in the studies using the Corsi test, the bilingual effect emerges only when an easier version of the task was used (Frog Task Matrix).

The studies included in this systematic review provide an overview of the variability of the population considered in studies on bilingualism. Some studies include bilingual participants who know different language pairs (e.g., Engel de Abreu, 2011 ; Friesen et al., 2015 ), and other participants who are children of immigrants who may face different cultural, family and social contexts (e.g., Leikin and Tovli, 2014 ; Ladas et al., 2015 ). Moreover, information about the acquisition and the use of known languages is not always given, and it does not allow determining the type of bilingualism (i.e., simultaneous or sequential) or the interactional context. Information, such as the age of acquisition of the first and second language, the degree of exposure, and the daily use of the languages, would lead to select better bilinguals. It could allow verifying the possible effects of these characteristics. Knowing the same languages does not determine having shared the same bilingual experience because the interactional contexts in which languages are used may not be the same ( Antoniou, 2019 ). Most studies included in this review do not include information about the context in which language exchanges occur, and linguistic contexts can be very different.

For the classification of participants in bilinguals and monolinguals, parental and self-reports are usually used as they are considered reliable instruments for evaluating experience related to second language acquisition ( Gutiérrez–Clellen and Kreiter, 2003 ; Bedore et al., 2011 ). The lack of detailed information about the bilingual experience could lead to an incorrect classification of the participants, not allowing them to detect any differences. This problem is highlighted by Poarch and Bialystok (2015) , who included a group of partial bilinguals (i.e., native speakers of English who had been learning French for about 2 years) that achieved the same performance as monolinguals. The inclusion of these participants in the bilingual group would have nullified the difference in performance between bilinguals and monolinguals. Another aspect to consider is when children begin formal school education. When children begin school, they are exposed to one or more foreign languages depending on the educational program. Therefore, information on the weekly frequency of exposure and use of the foreign language should be collected.

Some sociodemographic factors, such as low socioeconomic or immigrant status, affect the development of executive functions. Frequently migrant population has a low socioeconomic status, and their bilingualism is often secondary to the migration in a foreign country. In America, there is a high association between low SES and bilingualism. Several studies confirm that belonging to families with low socioeconomic status has negative consequences on the development of different cognitive functions and language skills. In this adverse situation, bilingualism seems to act as a protective factor ( Hartanto et al., 2019 ); in fact, some studies (e.g., Engel de Abreu et al., 2012 ; Krizman et al., 2016 ) reported an advantage of bilingual participants when the socioeconomic status was controlled. The cognitive advantage of bilingualism can be developed independently by the SES ( Blom et al., 2014 ; Calvo and Bialystok, 2014 ).

Further, it needs to clarify at which specific point in the lifespan the bilingual effect should be studied. The strongest evidence supporting the bilingual effect comes from studies that have included participants with executive functions that are not at a maximum level (e.g., older people). The bilingual effect should be evident in children because they have not yet reached the full development of cognitive functions ( Antón et al., 2014 ). Most of the studies in this review investigated the existence of the bilingual effect in children between 5 and 9 years of age. Only thirteen studies included early adolescent participants (10–14 years), while none included middle adolescent participants (15–17 years). The longitudinal study by Park et al. (2018) showed that results could be influenced by time points when individuals are tested and that the various components of the executive functions would seem to follow different trajectories of development. In this study, the bilinguals and monolinguals achieved the same performance when individuals were tested for updating abilities while a bilingual effect in inhibition skills emerged at time 2 but not at time 1. Finally, an advantage was found for the bilingual group in terms of shifting abilities at both times 1 and 2 for mixing cost, while no advantage was found for shifting and switching cost. In addition to age, the test used would also seem to influence the results: in Struys et al. (2018) in which groups of participants of different ages were compared, a smaller congruency effect was found in the group of younger bilinguals (mean age 6.6 years) on the Simon task and a smaller congruency effect for older bilinguals (mean age 11.7 years) on the flanker task. Longitudinal studies should be conducted to investigate whether bilingualism affects the development trajectories of executive functions. It is still unclear how much “training” of the executive functions (in terms of years or time spent on the use of the two languages) is necessary to produce a difference between bilinguals and monolinguals and, therefore, when the condition of bilingualism generates an advantage.

Limitations

This systematic review of the literature has not reached a definitive conclusion about the bilingual effect. This limitation is due to the high variability of the results observed by the different studies. Moreover, as Leivada et al. (2020) recently pointed out, systematic reviews assume that a comparison is made among studies that include similar populations, which is often not the case with these bilingual studies. In the studies on bilingualism, the adoption of a dichotomous “monolingual vs. bilingual” approach and the absence of a shared definition of bilingualism has led to an oversimplification of reality and the inclusion of individuals with very different characteristics in the same group. DeLuca et al. (2019) suggested the need to consider bilingualism as a spectrum of experiences that can affect neural plasticity. Moreover, the monolingual group also presents a degree of variability that should not be ignored ( Baum and Titone, 2014 ). Several aspects of the experience of individuals or groups would seem to affect brain adaptation differently. A quantitative analysis of the literature would have allowed stronger conclusions, but it was impossible to use a metanalytic approach because of the variability of the experimental tasks adopted in the different researches. Comparing the effects size and statistical analysis of the various studies could help to understand the results better. Future studies should analyze the characteristics of the participants more, and verify which factors, such as the AoA or the daily use of each language, influence the results.

Conclusions

The results summarized in this systematic review indicate the need for further studies that should consider the factors that have been identified as possible modulators of the observed results. Future studies should provide more information about the language context in which bilingual participants are immersed. It would be useful to establish guidelines identifying the minimum information needed to be included in the studies for the description of the bilingual population. Several researchers have highlighted the need to adopt a new approach to the study of this topic. Large-scale research projects involving several laboratories worldwide would provide clearer answers about the existence of a positive effect of bilingualism and identify the variables involved in this process ( Baum and Titone, 2014 ; Leivada et al., 2020 ). From the summary of the studies included in this systematic review, it emerges that current evidence does not make it possible to establish the existence of a bilingual effect or to identify the factors involved in determining the bilingual effect. Since bilingualism is a reality concerning a substantial percentage of the population, it is important to clarify this topic. A result in favor of the existence of the bilingual effect would provide the incentive for the implementation of bilingual school programs that could lead to extensive and regular use of more than one language. On the contrary, a reduction in performance linked to the condition of bilingualism would indicate the need to develop support programs aimed at those who, due to various circumstances, such as immigrant status or bilingual school education, are facing this situation. Executive functions are included in life skills, i.e., psychosocial skills that, if properly trained, enable the prevention of social and health problems, the promotion of social and personal development, and the protection of human rights. The absence of specific tests for the evaluation of bilinguals suggests the need to develop ad hoc instruments or to provide the validation of existing tests for this specific population. Tests containing verbal stimuli, used to make diagnoses, could lead to an overestimation of the problems. It would be useful to conduct a further systematic review focusing on the adult population to analyze the effect of bilingualism on those who have reached a peak or are in a phase of decline of executive functions.

Data Availability Statement

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author/s.

Author Contributions

JG and MC: conceptualization of the review, literature search, writing of the original draft, revision, and editing of the manuscript. DM: conceptualization of the review, writing of the original draft, revision, and editing. FF and SP: revision and editing of the manuscript. All authors contributed to the article and approved the submitted version.

This work was supported by FONDECYT 1181472 of the National Commission for Scientific and Technological Research of Chile, and project 21172/IV/19 granted by Fundación Séneca-Agencia de Ciencia y Tecnología de la Región de Murcia (Spain).

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Keywords: bilingualism, executive functions, bilingual advantage, inhibition, shifting, working memory

Citation: Giovannoli J, Martella D, Federico F, Pirchio S and Casagrande M (2020) The Impact of Bilingualism on Executive Functions in Children and Adolescents: A Systematic Review Based on the PRISMA Method. Front. Psychol. 11:574789. doi: 10.3389/fpsyg.2020.574789

Received: 21 June 2020; Accepted: 24 August 2020; Published: 06 October 2020.

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Copyright © 2020 Giovannoli, Martella, Federico, Pirchio and Casagrande. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Jasmine Giovannoli, jasmine.giovannoli@uniroma1.it ; Maria Casagrande, maria.casagrande@uniroma1.it

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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Article contents

Bilingualism and multilingualism from a socio-psychological perspective.

• Tej K. Bhatia Tej K. Bhatia Department of Linguistics, Syracuse University
• https://doi.org/10.1093/acrefore/9780199384655.013.82
• Published online: 28 June 2017

Bilingualism/multilingualism is a natural phenomenon worldwide. Unwittingly, however, monolingualism has been used as a standard to characterize and define bilingualism/multilingualism in linguistic research. Such a conception led to a “fractional,” “irregular,” and “distorted” view of bilingualism, which is becoming rapidly outmoded in the light of multipronged, rapidly growing interdisciplinary research. This article presents a complex and holistic view of bilinguals and multilinguals on conceptual, theoretical, and pragmatic/applied grounds. In that process, it attempts to explain why bilinguals are not a mere composite of two monolinguals. If bilinguals were a clone of two monolinguals, the study of bilingualism would not merit any substantive consideration in order to come to grips with bilingualism; all one would have to do is focus on the study of a monolingual person. Interestingly, even the two bilinguals are not clones of each other, let alone bilinguals as a set of two monolinguals. This paper examines the multiple worlds of bilinguals in terms of their social life and social interaction. The intricate problem of defining and describing bilinguals is addressed; their process and end result of becoming bilinguals is explored alongside their verbal interactions and language organization in the brain. The role of social and political bilingualism is also explored as it interacts with individual bilingualism and global bilingualism (e.g., the issue of language endangerment and language death).

Other central concepts such as individuals’ bilingual language attitudes, language choices, and consequences are addressed, which set bilinguals apart from monolinguals. Language acquisition is as much an innate, biological, as social phenomenon; these two complementary dimensions receive consideration in this article along with the educational issues of school performance by bilinguals. Is bilingualism a blessing or a curse? The linguistic and cognitive consequences of individual, societal, and political bilingualism are examined.

• defining bilinguals
• conceptual view of bilingualism
• becoming bilingual
• social networks
• language organization of bilinguals
• the bilingual mind
• bilingual language choices
• language mixing
• code-mixing/switching
• bilingual identities
• consequences of bilingualism
• bilingual creativity
• and political bilingualism

1. Understanding Multilingualism in Context

In a world in which people are increasingly mobile and ethnically self-aware, living with not just a single but multiple identities, questions concerning bilingualism and multilingualism take on increasing importance from both scholarly and pragmatic points of view. Over the last two decades in which linguistic/ethnic communities that had previously been politically submerged, persecuted, and geographically isolated, have asserted themselves and provided scholars with new opportunities to study the phenomena of individual and societal bilingualism and multilingualism that had previously been practically closed to them. Advances in social media and technology (e.g., iPhones and Big Data Capabilities) have rendered new tools to study bilingualism in a more naturalistic setting. At the same time, these developments have posed new practical challenges in such areas as language acquisition, language identities, language attitudes, language education, language endangerment and loss, and language rights.

The investigation of bi- and multilingualism is a broad and complex field. Unless otherwise relevant on substantive grounds, the term “bilingualism” in this article is used as an all-inclusive term to embody both bilingualism and multilingualism.

2. Bilingualism as a Natural Global Phenomenon: Becoming Bilingual

Bilingualism is not entirely a recent development; for instance, it constituted a grassroots phenomenon in India and Africa since the pre-Christian era. Contrary to a widespread perception, particularly in some primarily monolingual countries—for instance, Japan or China—or native English-speaking countries, such as the United States, bilingualism or even multilingualism is not a rare or exceptional phenomenon in the modern world; it was and it is, in fact, more widespread and natural than monolingualism. The Ethnologue in the 16th edition ( 2009 , http://www.ethnologue.com/show_country.asp?name=lb ) estimates more than seven thousand languages (7,358) while the U.S. Department of States recognizes only 194 bilingual countries in the world. There are approximately 239 and 2,269 languages identified in Europe and Asia, respectively. According to Ethnologue , 94% of the world’s population employs approximately 5% of its language resources. Furthermore, many languages such as Hindi, Chinese, Arabic, Bengali, Punjabi, Spanish, and Portuguese are spoken in many countries around the globe. Such a linguistic situation necessitates people to live with bilingualism and/or multilingualism. For an in-depth analysis of global bilingualism, see Bhatia and Ritchie ( 2013 ).

3. Describing Bilingualism

Unlike monolingualism, childhood bilingualism is not the only source and stage of acquiring two or more languages. Bilingualism is a lifelong process involving a host of factors (e.g., marriage, immigration, and education), different processes (e.g., input conditions, input types, input modalities and age), and yielding differential end results in terms of differential stages of fossilization and learning curve (U-shape or nonlinear curve during their grammar and interactional development). For this reason, it does not come as a surprise that defining, describing, and categorizing a bilingual is not as simplistic as defining a monolingual person. In addition to individual bilingualism, social and political bilingualism adds yet other dimensions to understanding bilingualism. Naturally then, there is no universally agreed upon definition of a bilingual person.

Bilingual individuals are subjected to a wide variety of labels, scales, and dichotomies, which constitute a basis of debates over what is bilingualism and who is a bilingual. Before shedding light on the complexity of “individual” bilingualism, one should bear in mind that the notion of individual bilingualism is not devoid of social bilingualism, or an absence of a shared social or group grammar. The term “individual” bilingualism by no means refers to idiosyncratic aspects of bilinguals, which is outside the scope of this work.

Relying on a Chomskyan research paradigm, bilingualism is approached from the theoretical distinction of competence vs. performance (actual use). Equal competency and fluency in both languages—an absolute clone of two monolinguals without a trace of accent from either language—is one view of a bilingual person. This view can be characterized as the “maximal” view. Bloomfield’s definition of a bilingual with “a native-like control of two languages” attempts to embody the “maximal” viewpoint (Bloomfield, 1933 ). Other terms used to describe such individuals are “ambilinguals” or “true bilinguals.” Such bilinguals are rare, or what Valdes terms, “mythical bilingual” (Valdes, 2001 ). In contrast to maximal view, a “minimal” view contends that practically every one is a bilingual. “That is no one in the world (no adult, anyway) which does not know at least a few words in languages other than the maternal variety” (Edwards, 2004/2006 ). Diebold’s notion of “Incipient bilingualism”—that is, exposure to two languages—belongs to the minimal view of bilingualism (Diebold, 1964 ). While central to the minimalist viewpoint is the onset point of the process of becoming a bilingual, the main focus of the maximalist view is the end result, or termination point, of language acquisition. In other words, the issue of degree and the end state of second language acquisition is at the heart of defining the concept of bilingualism.

Other researchers such as Mackey, Weinreich, and Haugen define bilingualism to capture language use of bilinguals’ verbal behavior. For Haugen, bilingualism begins when the speakers of one language produce complete meaningful utterances in the second language (Haugen, 1953 ; Mackey, 2000 ; Weinrich, 1953 ). Mackey, on the other hand, defines bilingualism as an “alternate use of two or more languages” (Mackey, 2000 ). Observe that the main objective of the two definitions is to focus on language use rather the degree of language proficiency or equal competency in two languages.

The other notable types of bilingualism identified are as follows: Primary/Natural bilingualism in which bilingualism is acquired in a natural setting without any formal training; Balanced bilingualism that develops with minimal interference from both languages; Receptive or Passive bilingualism wherein there is understanding of written and/or spoken proficiency in second language but an inability to speak it; Productive bilingualism then entails an ability to understand and speak a second language; Semilingualism, or an inability to express in either language; and Bicultural bilingualism vs. Monocultural bilingualism. The other types of bilingualism, such as Simultaneous vs. Successive bilingualism (Wang, 2008 ), Additive vs. Subtractive bilingualism (Cummins, 2000 ), and Elite vs. Folk bilingualism (Skutnabb-Kangas, 1981 ), will be detailed later in this chapter. From this rich range of scales and dichotomies, it becomes readily self-evident that the complexity of bilingualism and severe limitation of the “fractional” view of bilingualism that bilinguals are two monolinguals in one brain. Each case of bilingualism is a product of different sets of circumstances and, as a result, no two bilinguals are the same. In other words, differences in the context of second language acquisition (natural, as in the case of children) and proficiency in spoken, written, reading, and listening skills in the second language, together with the consideration of culture, add further complexity to defining individual bilingualism.

3.1 Individual Bilingualism: A Profile

The profile of this author further highlights the problems and challenges of defining and describing a bilingual or multilingual person. The author, as an immigrant child growing up in India, acquired two languages by birth: Saraiki—also called Multani and Lahanda, spoken primarily in Pakistan—and Punjabi, which is spoken both in India and Pakistan. Growing up in the Hindi-speaking area, he learned the third language Hindi-Urdu primarily in schools; and his fourth language, English, primarily after puberty during his higher education in India and the United States. He cannot write or read in Saraiki but can read Punjabi in Gurmukhi script, and he cannot write with the same proficiency. He has native proficiency in speaking, listening, reading, and writing. A close analysis of his bilingualism reveals that no single label or category accounts for his multifaceted bilingualism/multilingualism. Interestingly, his self-assessment finds him linguistically least secured in his two languages, which he acquired at birth. Is he a semilingual without a mother tongue? No matter how challenging it is to come to grips with bilingualism and, consequently, develop a “holistic” view of bilingualism, it is clear that a bilingual person demonstrates many complex attributes rarely seen in a monolingual person. See Edwards ( 2004/2006 ) and Wei ( 2013 ) for more details. Most important, multiple languages serve as a vehicle to mark multiple identities (e.g., religious, regional, national, ethnic, etc.).

3.2 Social Bilingualism

While social bilingualism embodies linguistic dimensions of individual bilingualism, a host of social, attitudinal, educational, and historical aspects of bilingualism primarily determine the nature of social bilingualism. Social bilingualism refers to the interrelationship between linguistic and non-linguistic factors such as social evaluation/value judgements of bilingualism, which determine the nature of language contact, language maintenance and shift, and bilingual education among others. For instance, in some societies, bilingualism is valued and receives positive evaluation and is, thus, encouraged while in other societies bilingualism is seen as a negative and divisive force and is, thus, suppressed or even banned in public and educational arenas. Compare the pattern of intergenerational bilingualism in India and the United states, where it is well-known that second or third-generation immigrants in the United States lose their ethnic languages and turn monolinguals in English (Fishman, Nahirny, Hofman, & Hayden, 1966 ). Conversely, Bengali or Punjabi immigrants living in Delhi, generation after generation, do not become monolinguals in Hindi, the dominant language of Delhi. Similarly, elite bilingualism vs. folk bilingualism has historically prevailed in Europe, Asia, and other continents and has gained a new dimension in the rapidly evolving globalized society. As aristocratic society patronized bilingualism with French or Latin in Europe, bilingualism served as a source of elitism in South Asia in different ages of Persian and English. Folk bilingualism is often the byproduct of social dominance and imposition of a dominant group. While elite bilingualism is viewed as an asset, folk bilingualism is seen as problematic both in social and educational arenas (Skutnabb-Kangas, 1981 ). One of the outcomes of a stable elite and folk bilingualism is diglossia (e.g., Arabic, German, Greek, and Tamil) where both High (elite) and Low (colloquial) varieties of a language—or two languages with High and Low social distinctions—coexist (e.g., French and English diglossia after the Norman conquest (Ferguson, 1959 ). Diasporic language varieties have been examined by Clyne and Kipp ( 1999 ) and Bhatia ( 2016 ). Works by Baker and Jones ( 1998 ) show how bilinguals belong to communities of variable types due to accommodation (Sachdev & Giles, 2004/2006 ), indexicality (Eckert & Rickford, 2001 ), social meaning of language attitudes (Giles & Watson, 2013 ; Sachdev & Bhatia, 2013 ), community of practice, and even imagined communities.

3.3 Political Bilingualism

Political bilingualism refers to the language policies of a country. Unlike individual bilingualism, categories such as monolingual, bilingual, and multilingual nations do not reflect the actual linguistic situation in a particular country (Edwards, 1995 , 2004/2006 ; Romaine, 1989/1995 ). Canada, for instance, is officially recognized as a bilingual country. This means that Canada promotes bilingualism as a language policy of the country as well as in Canadian society as a whole. By no means does it imply that most speakers in Canada are bilinguals. In fact, monolingual countries may reflect a high degree of bilingualism. Multilingual countries such as South Africa, Switzerland, Finland and Canada often use one of the two approaches—“Personality” and “Territorial”—to ensure bilingualism. The Personality principle aims to preserve individual rights (Extra & Gorter, 2008 ; Mackey, 1967 ) while the Territorial principle ensures bilingualism or multilingual within a particular area to a variable degree, as in the case of Belgium. In India, where 23 languages are officially recognized, the government’s language policies are very receptive to multilingualism. The “three-language formula” is the official language policy of the country (Annamalai, 2001 ). In addition to learning Hindi and English, the co-national languages, school children can learn a third language spoken within or outside their state.

4. The Bilingual Mind: Language Organization, Language Choices, and Verbal Behavior

Unlike monolinguals, a decision to speak multiple languages requires a complex unconscious process on the part of bilinguals. Since a monolingual’s choice is restricted to only one language, the decision to choose a language is relatively simple involving, at most, the choice of an informal style over a formal style or vice versa. However, the degree and the scale of language choice are much more complicated for bilinguals since they need to choose not only between different styles but also between different languages. It is a widely held belief, at least in some monolingual speech communities, that the process of language choice for bilinguals is a random one that can lead to a serious misunderstanding and a communication failure between monolinguals and bi- and multilingual communities (see pitfalls of a sting operation by a monolingual FBI agent (Ritchie & Bhatia, 2013 )). Such a misconception of bilingual verbal behavior is also responsible for communication misunderstandings about social motivations of bilinguals’ language choices by monolinguals; for example, the deliberate exclusion or sinister motives on the part of bilinguals when their language choice is different from a monolingual’s language. A number of my international students have reported that on several occasions monolingual English speakers feel compelled to remind them that they are in America and they should be using English, rather than say Chinese or Arabic, with countrymen/women.

Now let us examine some determinants of language choice by bilinguals. Consider the case of this author’s verbal behavior and linguistic choices that he normally makes while interacting with his family during a dinner table conversation in India. He shares two languages with his sisters-in-law (Punjabi and Hindi) and four languages with his brothers (Saraiki, Punjabi, Hindi, and English). While talking about family matters or other informal topics, he uses Punjabi with his sisters-in-law but Saraiki with his brothers. If the topic involves ethnicity, then the entire family switches to Punjabi. Matters of educational and political importance are expressed in English and Hindi, respectively. These are unmarked language choices, which the author makes unconsciously and effortlessly with constant language switching depending on participants, speech events, situations, or other factors. Such a behavior is largely in agreement with the sociolinguistic Model of Markedness, which attempts to explain the sociolinguistic motivation of code-switching by considering language choice as a means of communicating desired group membership, or perceived group memberships, and interpersonal relationships (Pavlenko, 2005 ).

Speaking Sariki with brothers and Punjabi with sister-in-laws represent unconscious and unmarked choices. Any shift to a marked choice is, of course, possible on theoretical grounds; however, it can take a serious toll in terms of social relationships. The use of Hindi or English during a general family dinner conversation (i.e., a “marked” choice) will necessarily signal social distancing and fractured relations.

Languages choice is not as simple as it seems at first from the above example of family conversation. In some cases, it involves a complex process of negotiation. Talking with a Punjabi-Hindi-English trilingual waiter in an Indian restaurant, the choice of ethnic language, Punjabi, by a customer such as this author may seem to be a natural choice at first. Often, it is not the case if the waiter refuses to match the language choice of the customer and replies in English. The failure to negotiate a language in such cases takes an interesting turn of language mismatching before a common language of verbal exchange is finally agreed upon; often, it turns out to be a neutral and prestige language: English. See Ritchie and Bhatia ( 2013 ) for further details. When the unmarked choice is not clear, speakers tend to use code-switching in an exploratory way to determine language choice and thus restore a social balance.

During a speech event, language choice is not always static either. If the topic of conversation shifts from a casual topic to a formal topic such as education, a more suitable choice in this domain would be English; subsequently, a naturally switch to English will take place. In other words, “complementarity” language domains or language-specific domain allocation represent the salient characteristics of bilingual language choice. The differential domain allocation manifests itself in the use of “public” vs. “private” language by bilinguals, which is central to bilingual verbal repertoire (Ritchie & Bhatia, 2013 ). Often the role of expressing emotions or one’s private world is best played by the bilingual’s mother tongue rather than by the second or prestige/distant language. Research on bilingualism, emotions, and autobiographical memory accounts of bilinguals shows that an account of emotional events is qualitatively and quantitatively different when narrated in one’s mother tongue than in a distant second language (Devaele, 2010 ; Pavlenko, 2005 ). While the content of an event can be narrated equally well in either language, the emotional experience/pain is best described in the first language of the speaker. Particularly, bilingual parents use their first language for terms of endearment for their children. Their first language serves as the best vehicle for denoting emotions toward their children than any other language in their verbal repertoire. Taboo topics, on the other hand, favor the second or a distant language.

Any attempt to characterize the bilingual mind must account for the following three natural aspects of bilingual verbal behavior: (1) Depending upon the communicative circumstances, bilinguals swing between the monolingual and bilingual language modes; (2) Bilinguals have an ability to keep two or more languages separate whenever needed; and (3) More interestingly, they can also carry out an integration of two or more languages within a speech event.

4.1 Bilingual Language Modes

Bilinguals are like a sliding switch who can move between one or more language states/modes as required for the production, comprehension, and processing of verbal messages in a most cost-effective and efficient way. If bilinguals are placed in a predominantly monolingual setting, they are likely to activate only one language; while in a bilingual environment, they can easily shift into a bilingual mode to a differential degree. The activation or deactivation process is not time consuming. In a bilingual environment, this process usually does not require bilinguals to take more than a couple of milliseconds to swing into a bilingual language mode and revert back to a monolingual mode with the same time efficiency. However, under unexpected circumstances (e.g., caught off-guard by a white Canadian speaking an African language in Canada) or under emotional trauma or cultural shock, the activation takes considerable time. In the longitudinal study of his daughter, Hildegard, reported that Hildegard, while in Germany, came to tears at one point when she could not activate her mother tongue, English (Leopard, 1939–1950 ). The failure to ensure natural conditions responsible for the activation of bilingual language mode is a common methodological shortcoming of bilingual language testing, see Grosjean ( 2004 / 2006 , 2010 ). An in-depth review of processing cost involved in the language activation-deactivation process can be found in Meuter ( 2005 ). Do bilinguals turn on their bilingual mode, even if only one language is needed to perform a task? Recent research employing an electrophysiological and experimental approach shows that both languages compete for selection even if only one language is needed to perform a task (Martin, Dering, Thomas, & Thierry, 2009 ; Hoshino & Thierry, 2010 ). For more recent works on parallel language activation and language competition in speech planning and speech production, see Blumenfeld and Marian ( 2013 ). In other words, the potential of activation and deactivation of language modes—both monolingual and bilingual mode—hold an important key to bilingual’s language use.

4.2 Bilingual Language Separation and Language Integration

In addition to language activation or deactivation control phenomena, the other two salient characteristics of bilingual verbal behavior are bilinguals’ balanced competence and capacity to separate the two linguistic systems and to integrate them within a sentence or a speech event. Language mixing is a far more complex cognitive ability than language separation. Yet, it is also very natural to bilinguals. Therefore, it is not surprising to observe the emergence of mixed systems such as Hinglish, Spanglish, Germlish, and so on, around the globe. Consider the following utterances:

Such a two-faceted phenomenon is termed as code-mixing (as in 1 and 2) and code-switching (as in 3). Code-mixing (CM) refers to the use of various linguistic units—words, phrases, clauses, and sentences—primarily from two participating grammatical systems within a sentence. While CM is intra-sentential, code-switching (CS) is an inter-sentential phenomenon. CM is constrained by grammatical principles and is motivated by socio-psychological factors. CS, on the other hand, is subject to discourse principles and is also motivated by socio-psychological factors.

Any unified treatment of the bilingual mind has to account for the language separation (i.e., CS) and language integration (CM) aspects of bilingual verbal competence, capacity, use, and creativity. In that process, it needs to address the following four key questions, which are central to an understanding the universal and scientific basis for the linguistic creativity of bilinguals.

Is language mixing a random or a systematic phenomenon?

What motivates bilinguals to mix and alternate two languages?

What is the social evaluation of this mixing and alternation?

What is the difference between code-mixing or code-switching and other related phenomena?

I. Language mixing as a systematic phenomenon

Earlier research from the 1950s–1970s concluded that CM is either a random or an unsystematic phenomenon. It was either without subject to formal syntactic constraints or is subject only to “irregular mixture” (Labov, 1971 ). Such a view of CM/CS is obsolete since late the 20th century . Recent research shows that CM/CS is subject to formal, functional, and attitudinal factors. Studies of formal factors in the occurrence of CM attempt to tap the unconscious knowledge of bilinguals about the internal structure of code-mixed sentences. Formal syntactic constraints on the grammar of CM, such as The Free Morpheme Constraint (Sankoff & Poplack, 1981 ); The Closed Class Constraint (Joshi, 1985 ), within the Generative Grammar framework; and The Government Constraint and the Functional Head Constraint within the non-lexicalist generative framework, demonstrate the complexity of uncovering universal constraints on CM; for details, see Bhatia and Ritchie ( 2009 ). Recently, the search for explanations of cross-linguistic generalizations about the phenomenon of CM, specifically in terms of independently justified principles of language structure and use, has taken two distinct forms. One approach is formulated in terms of the theory of linguistic competence within the framework of Chomsky’s Minimalist Program (MacSwan, 2009 ). The other approach—as best exemplified by the Matrix Language Frame (MLF) model (Myers-Scotton & Jake, 2001 ) is grounded in the theory of sentence production, particularly that of Levelt ( 1989 ). Herring and colleagues test the strengths and weaknesses of both a Minimalist Program approach and the MLF approach on explanatory grounds based on switches between determiner and their noun complements drawn from Spanish-English and Welsh-English data (Herring, Deuchar, Couto, & Quintanilla, 2010 ). Their work lends partial support to the two approaches.

II. Motivations for language mixing

While research on the universal grammar of CM attempts to unlock the mystery of the systematic nature of CM on universal grounds, it does not attempt to answer Question (II), namely, the “why” aspect of CM. The challenge for linguistic research in the new millennium is to separate grammatical constraints from those motivated by, or triggered by, socio-pragmatic factors or competence. Socio-pragmatic studies of CM reveal the following four factors, which trigger CM/CS: (1) the social roles and relationships of the participants (e.g., dual/multiple identities; social class); (2) situational factors (discourse topic and language domain allocation); (3) message-intrinsic consideration; (4) language attitudes, including social dominance and linguistic security. See Ritchie and Bhatia ( 2013 ) and Myers-Scotton ( 1998 ) for further details. The most commonly accepted rule is that language mixing signals either a change or a perceived change by speaker in the socio-psychological context of a speech event. In essence, CM/CS is motivated by the consideration of “optimization,” and it serves as an indispensable tool for meeting creative and innovative needs of bilinguals (Bhatia, 2011 ). A novel approach provides further insights into a discourse-functional motivation of CM, namely, coding of less predictable, high information-content meanings in one language and more predictable, lower information-content meanings in another language (Myslin & Levy, 2015 ).

III. Social evaluation of language mixing

Now let us return to Question (III). From the discussion of Questions (I and II), it is self-evident that complexity and multifaceted creativity underlies CM/CS in bilingual communication. Surprisingly, though, the social evaluation of a mixed system is largely negative. Even more interestingly, bilinguals themselves do not have a positive view of language mixing. It is the widely held belief on the part of the “guardians” of language (including the media) and puritans that any form of language mixing is a sign of unsystematic or decadent form of communication. Bilinguals are often mocked for their “bad” and “irregular” linguistic behavior. They are often characterized as individuals who have difficulty expressing themselves. Other labels such as “lazy” and “careless” are also often bestowed upon them. Furthermore, the guardians of language often accused them of destroying their linguistic heritage. For these reasons, it is not surprising that even bilinguals themselves become apologetic about their verbal behavior. They blame mixing on “memory lapse,” among other things, and promise to correct their verbal behavior, vowing not to mix languages. In spite of this, they cannot resist language mixing!

Table 1 illustrates the anomaly between the scientific reality of language mixing and its social perception. Social perception translates into the negative evaluation of mixed speech.

Table 1. Language Mixing (CM/CS) Anomaly (Adapted from Bhatia & Ritchie, 2008 , p. 15).

Backlash to mixing is not just restricted to societies and bilinguals; even governments get on the bandwagon. Some countries, such as the newly freed countries of the ex-Soviet Union and France, regulate or even ban mixing either by appointing “language police” or by passing laws to wipe out the perceived negative effects of “bad language” in the public domain. Asia is not an exception in this regard. A case in point is a recent article by Tan ( 2002 ) reporting that the Government of Singapore has banned the movie Talk Cock because it uses a mixed variety of English, called Singlish. Linguistic prescriptivism clearly played a central role in the decision. In spite of the near-universal negative evaluation associated with CM/CS, the benefits rendered by language mixing by far outweigh its negative perception, which, in turn, compels the unconscious mind of bilinguals to mix and switch in order to yield results that cannot be rendered by a single/puritan language use; for a typology of bilingual linguistic creativity, and socio-psychological motivations, see Ritchie and Bhatia ( 2013 ).

IV. Language mixing and other related phenomena

Returning to the fourth question, it should be noted that CM/CS is quite distinct from linguistic borrowing. The primary function of linguistic borrowing is to fill a lexical gap in a borrower’s language (e.g., Internet, satellite). Furthermore, with borrowing, the structure of the host language remains undisturbed. However, CM requires complex integrity of two linguistic systems/grammar within a sentence, which may yield a new grammar. Other mixed systems, such as pidgin and creole languages, often fail to match the complexity and creativity of CM/CS. The distinction between code-mixing and code-switching is controversial for a number of reasons, particularly the integration of the participating grammar’s intrasententially details; see Bhatia and Ritchie ( 2009 ). Additionally, Deuchar and Stammers ( 2016 ) claim that code-switches and borrowings are distinct on the basis of frequency and degree of integration. Specifically, only the former are low in both frequency and integration. For details about contrasting and comparing different positions on this issue, see Myslin & Levy ( 2015 ); Poplack and Meechan ( 1998 ); and Lakshmanan, Balam, and Bhatia ( 2016 ). Furthermore, there is a debatable distinction between CM and Translanguaging (Garcia & Wei, 2014 ).

5. Bilingual Language Development: Nature vs. Nurture

Beyond innateness (e.g., nature, Biolinguistic and Neurological basis of language acquisition), social factors play a critical play in the language development of bilinguals. As pointed out earlier, describing and defining bilingualism is a formidable task. This is due to the fact that attaining bilingualism is a lifelong process; a complex array of conditions gives rise to the development of language among bilinguals. Based on the recommendation of educators, among others, bilingual families usually adopt a “One-Parent/One-Language” strategy with different combinations, such as language allocation based on time and space; for example, using one language in the morning and other in the evening or one language in the kitchen and another in the living room. This is done to maintain minority language. In spite of their obvious potential benefits for language maintenance, such strategies fall short in raising bilingual and bicultural children for a number of reasons, including imparting pragmatic and communicative competence and providing negative and positive evidence to children undergoing heritage language development with sociolinguistically real verbal interactional patterns (Bhatia & Ritchie, 1995 ). Therefore, De Houwer ( 2007 ) rightly points out that it is important for children to be receiving language input in the minority language from both parents at home. This also represents a common practice in non-Western societies in Asia (e.g., India) and Africa (e.g., Nigeria) where both parents, including members of the joint family minority languages, speak in their minority language.

While raising bilingual children does not pose any serious challenge for majority children (e.g., English-speaking children learning French in Canada), it is a different story for minority or heritage children. Sadly, a complex mix of political and social bilingualism leads heritage/minority parents, who themselves experience adverse discrimination in social and work settings, simply to prohibit the use of minority languages in family and educational environments. This practice, no matter how well intended, often results in negative school performance and emotional problems for minority children.

6. Simultaneous vs. Sequential Childhood Bilingualism

Broadly speaking, childhood bilingualism can manifest itself in two distinct patterns: (1) Simultaneous bilingualism and (2) Sequential bilingualism. A child being exposed to two languages to more or less to the same degree from birth onward is described as a simultaneous bilingual; conversely, a child being exposed to one language first followed by a second language, with the latter coming after the age of five, is referred to as sequential bilingual. Sequential bilingualism takes place either in schools or in peer groups and/or family settings. Surely, sequential bilingualism can persist throughout the adulthood. How is early bilingualism different from late bilingualism? Research on sequential and adult language acquisition shows that the pattern of sequential/successive language acquisition falls somewhere in the middle of the continuum between a simultaneous bilingual and an adult language learner.

7. Adult Bilingualism: UG and Native Language Dominance

Why is the task of learning a second language by adults more difficult and time consuming than by children? In spite of considerable motivation and effort, why do adults fall short of achieving native-like competency in their target language? Why do even very competent and balanced bilinguals speak with an “accent”? The Critical Period Hypothesis by Lenneberg ( 1967 ) attempts to answer these questions, and it is sensitive to age (Lenneberg, 1967 ). Children are better equipped to acquire languages because their brains are more “plastic” before they hit maturity. They have access to UG, to which adults have either no access or only partial access. Afterward, the loss of plasticity results in the completion of lateralization of language function in the left hemisphere. Even though adults are more cognitively developed and exhibit a high degree of aptitude, they have to rely on their native language (L1 transference—including “foreign accent” together with morphological features) in the process of learning a second language (Gass, 1996 ). Then there comes a time when their ultimate attainment of L2 falls short of the native language target, termed “fossilization” stage. No amount of training allows them to bypass this stage to free themselves from second language errors. Siegel, for instance, offers an alternative explanation of the language attainment state termed fossilization in second language acquisition research—a stage of falling short of attaining a native-speaker end grammar (Siegel, 2003 ). He argues that fossilization is not biologically driven but is the reflection of learners’ decisions not to clone the native speaker’s norm in order to index their own identity. Some researchers believe that this stage does not have a biological basis; instead, it is the result of bilingual, dual, or multiple identities. Adult learners are not ready to give up their identity and, as a result, this prevents them from having a perfect native-like competency of L2. For alternative theories of language acquisition, see, for example, a usage-based approach by Tomasello ( 2003 ); and the Dynamic System Theory by De Bot, Wander, and Verspoor ( 2007 ).

The differential competencies, as evident from the different types of adult bilinguals, can be accounted for primarily on sociolinguistic grounds. For instance, gender or the period of residency in a host country yields the qualitative and quantitative differences in bilingual language acquisition. Factors such as access to workplace, education, relationship, social networks, exogamic marriage, religion, and other factors lead to differential male and female bilingualism in qualitative grounds (Piller & Pavlenko, 2004/2006 ). Additionally, learners’ type, their aptitude, and attitude also contribute to a variable degree of language learning curves. Instrumental learners who learn a second language for external gains tend to lag behind Integrative learners who aim at integration with the target culture. Similarly, the Social Accommodation Theory (Sachdev & Giles, 2004/2006 ) attempts to explain differences in language choices and consequences on one hand and the social evaluation of speech (good vs. bad accents) on the other, which influence the social-psychological aspects of bilingual verbal interaction in different social settings (Altarriba & Moirier, 2004/2006 ; Lippi-Green, 2012 ).

8. Effects of Bilingualism

Until the middle of the 20th century in the United States, researchers engaged in examining the relationship between intelligence and bilingualism concluded that bilingualism has serious adverse effects on early childhood development. Such findings led to the development of the “factional” view of bilingualism, which was grounded in a flawed monolingual perspective on the limited linguistic capacity of the brain on one hand and the Linguistic Deficit Hypothesis on the other.

Their line of argument was that crowding the brain with two languages leads to a variety of impairments in both the linguistic and the cognitive abilities of the child. Naturally, then, they suggested that bilingual children not only suffer from semilingualism (i.e., lacking proficiency both in their mother tongue and the second language) and stuttering, etc., but also from low intelligence, mental retardation, left handedness, and even schizophrenia.

It took more than half a century before a more accurate and positive view of bilingualism emerged. The main credit for this goes to the pioneering work of Peal and Lambert ( 1962 ), which revealed the actual benefits of bilingualism. The view of bilingualism that subsequently emerged can be characterized as the Linguistic Augmentation Hypothesis (Peal & Lambert, 1962 ). Peal and Lambert studied earlier balanced bilingual children and controlled for factors such as socioeconomic status. Sound on methodological grounds, their result showed bilinguals to be intellectually superior to their monolingual counterparts. Their study, which was conducted in Montreal, changed the face of research on bilingualism. Many studies conducted around the globe have replicated the findings of Peal and Lambert. In short, cognitive, cultural, economic, and cross-cultural communication advantages of childhood and lifelong bilingualism are many, including reversing the effects of aging (Bialystok, 2005 ; Hakuta, 1986 ). Nevertheless, the effects of bilingualism on children’s cognitive development, particularly on executive function and attention, is far from conclusive; see Klein ( 2015 ) and Bialystok ( 2015 ).

9. Bilingualism: Language Spread, Maintenance, Endangerment, and Death

Language contact and its consequences represent the core of theoretical and descriptive linguistic studies devoted to bilingualism, and onto which globalization has added a new dimension. Ironically, in the age of globalization, the spread of English and other Indo-European languages, namely, Spanish and Portuguese, has led to the rise of bilingualism induced by these languages; they also pose a threat to the linguistic diversity of the world. Researchers claim that about half the known languages of the world have already vanished in the last 500 years, and that at least half, if not more, of the 6,909 living languages will become extinct in the next century (Hale, 1992 ; Nettle & Romaine, 2000 ). Research on language maintenance, language shift, and language death addresses the questions of why and how some languages spread and others die. Phillipson and Mufwene attempt to account for language endangerment within the framework of language imperialism ( 2010 ) and language ecology ( 2001 ), respectively. Fishman ( 2013 ) examines the ways to reverse the tide of language endangerment. Skutnabb-Kangas views minority language maintenance as a human rights issue in public and educational arenas ( 1953 ).

Critical Analysis of Scholarship

Advances in our understanding of bilingualism have come a long way since the predominance of the “factional” and linguistically deficient view of bilingualism. The complexity and diverse conditions responsible for lifelong bilingualism has led to a better understanding of this phenomenon on theoretical, methodological, and analytical grounds. A paradigm shift from monolingualism and the emergence of a new, interdisciplinary approach promises new challenges and directions in the future study of bilingualism.

Issues and Conceptualization

Although bilingualism is undoubtedly a widespread global phenomenon, it is rather ironic that, for a number of reasons, including the primary objective of linguistics, multidimensional aspects of bilingualism, and misperception of bilingualism as a rare phenomenon, the study of bilingualism has posed—and continues to pose—a serious of challenges to linguistics for quite some time. This is evident from eminent linguist Roman Jacobson’s observation from more than half a century ago: “bilingualism is for me a fundamental problem of linguistics” (Chomsky, 1986 ). Similarly, Chomsky remarked that the pure idealized form of language knowledge should be the first object of study rather than the muddy water of bilingualism (Grosjean, 1989 ). Consequently, research on bilingualism has taken a backseat to monolingualism, and monolinguals have served as a benchmark to characterize and theorize bilinguals, which, in turn, led to the ill conceptualization of the bilingual person as “two monolinguals in one brain” (Dehaene, 1999 ).

Are bilinguals just a composite or sum of two monolinguals crowded in one brain? A large body of research devoted to the bilingualism and intelligence debate either implicitly or explicitly subscribed to the “two monolinguals in one brain” conception. This set the stage for the “linguistic deficiency hypothesis” about bilingual children and adults on one hand and the limited linguistic capacity of the brain on the other. When looking from the lens of monolingualism, a “factional view” (Bhatia & Ritchie, 2016 ; Nicol, 2001 ), or even distorted view, of bilingualism emerged that portrayed bilinguals as semilinguals with a lack of proficiency not just in one but two languages. Although still in its infant stage, from recent research on bilingualism, a more accurate or holistic view of a bilingual and multilingual person has begun to emerge in 1990s, namely, just as an individual bilingual does not constitute two monolinguals in one brain, a multilingual is not merely a byproduct of bilingualism alone or vice versa. Similarly, the notion that brain capacity is ideally suited for one language is a myth. Additionally and interestingly, no two bilinguals behave the same way all the time since they are not a clone of each other.

Bilingualism, unlike monolingualism, exhibits complex individual, social, political, psychological, and educational dimensions in addition to involving a complex interaction of two or more languages in terms of coexistence, competition, and cooperation of two linguistic systems. Additionally, although bilingualism is a lifelong process, the language development among bilinguals is not merely a linear process; there are turns and twists on the way to becoming bilingual, trilingual, and multilingual. The path to trilingualism is even more complex than growing up with two languages (Bhatia & Ritchie, 2016 ).

The role of sociolinguistic factors in language learning; language use (creativity); language maintenance; and language shift, particularly in trilingual language acquisition and use, opens new challenging areas of future research. The main challenge for theoreticians and practitioners is how to come to grips with various facets of the bilingual brain ranging from language contact, bilingual language interaction, to language modes of the bilingual mind/brain on one hand and methodological issues on the other.

Despite a number of studies on the Critical Period Hypothesis, and other competing hypotheses of bilingual language acquisition, future research in cognitive aptitude, age, and multiple language effects with the lens of interdisciplinary debatable findings and methodologies continues to pose new challenges and promises to the field of bilingualism (Long, 2016 ).

Further Reading

• Auer, P. , & Wei, L. (Eds.). (2007). Handbook of multilingualism and multilingual communication . Berlin: Mouton de Gruyter.
• Bhatia, T. , & Ritchie, W. (2004/2006). The handbook of bilingualism . Oxford: Wiley-Blackwell.
• Bhatia, T. , & Ritchie, W. (2013). The handbook of bilingualism and multilingualism . Oxford: Wiley-Blackwell.
• Ferreira, A. , & Schwieter, J. W. (Eds.). (2015). Psycholinguistic and cognitive inquiries into translation and interpreting . Amsterdam: Benjamins.
• Heredia, R. , & Cieś licka, A. (Eds.). (2015). Bilingual figurative language processing . New York: Cambridge University Press.
• Schwieter, J. W. (Ed.). (2015). The Cambridge handbook of bilingual processing . Cambridge, U.K.: Cambridge University Press.

Foundational Works

• Bialystok, E. , & Hakuta, K. (1994). In other words: The science and psychology of second language acquisition . New York: Basic Books.
• Cummins, J. (2000). Language, power and pedagogy: Bilingual children in the cross-fire . Clevedon, U.K.: Multilingual Matters.
• Edwards, J. R. (1994). Multilingualism . London: Routledge.
• Grosjean, F. (2008). Studying bilinguals . Oxford: Oxford University Press.
• Haugen, E. (1953). The Norwegian language in America: A study in bilingual behavior . Philadelphia: University of Pennsylvania Press.
• Mackey, W. F. (1967). Bilingualism as a world problem/Le bilinguïsme: Phenomène mondial . Montreal, QC: Harvest House.
• Romaine, S. (1995). Bilingualism (2d ed.). Oxford: Blackwell.
• Weinreich, U. (1953). Languages in contact: Findings and problems . The Hague, The Netherlands: Mouton.

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Language Disorders Research on Bilingualism, School-Age, and Related Difficulties: A Scoping Review of Descriptive Studies

Associated data, background:.

Developmental language disorder (DLD) often remains undetected until children shift from ‘learning to read’ to ‘reading to learn,’ around 9 years of age. Mono- and bilingual children with DLD frequently have co-occurring reading, attention, and related difficulties, compared to children with typical language development (TLD). Data for mono- and bilingual children with DLD and TLD would aid differentiation of language differences versus disorders in bilingual children.

We conducted a scoping review of descriptive research on mono-and bilingual children < and >= 9 years old with DLD versus TLD, and related skills (auditory processing, attention, cognition, executive function, and reading).

Data Sources:

We searched PubMed for the terms “bilingual” and “language disorders” or “impairment” and “child[ren]” from August 1, 1979 through October 1, 2018.

Charting Methods:

Two abstracters charted all search results. Main exclusions were: secondary data/reviews, special populations, intervention studies, and case studies/series. Abstracted data included age, related skills measures’, and four language groups of participants: monolingual DLD, monolingual TLD, bilingual DLD, and bilingual TLD.

Of 366 articles, 159 (43%) met inclusion criteria. Relatively few (14%, n = 22) included all 4 language groups, co-occurring difficulties other than nonverbal intelligence (n = 49, 31%) or reading (n = 51, 32%) or any 9–18 year-olds (31%, n = 48). Just 5 (3%) included only 9–18 year-olds. Among studies with any 9 to 18 year olds, just 4 (8%, 4/48) included 4 language groups.

Conclusions:

Future research should include mono- and bilingual children with both DLD and TLD, beyond 8 years of age, along with data about their related skills.

Speech and language disorders occur in approximately 7% of children ages 3 to 17 years in the United States 1 and represent the second most common disability (at 20%) among children receiving special education in the United States. 2 Developmental Language Disorders (DLD), previously called specific language impairment or SLI) refer to a long-standing condition, not associated with any other medical or causal conditions, where children have problems understanding and using spoken language. 3 , 4 Outside the field of communications science, DLD receives scant attention compared to other, less prevalent developmental disabilities, including autism, attention deficit/hyperactivity disorder (ADHD), learning, and intellectual disabilities. 5 , 6 DLD is most often diagnosed in childhood, but the co-morbid conditions associated with it continue to affect functioning throughout one’s life. For example, DLD often leads to learning disabilities in school-aged children 7 and can continue to restrict a person’s social and academic performance well beyond adolescence into adulthood. 8 , 9

Differentiating a language disorder from normal language acquisition in bilingual speakers can be challenging for clinicians and educators. As bilingualism has become increasingly prevalent, the scope of this challenge is significant. In 2018, 23% of school-aged children nationwide spoke a language other than English at home. 10 English learners (ELs) comprised 10% of public school students in the 2017–2018 academic year, a 2% increase from 2000 to 2001. ELs may need 3 to 7 years to converge with native English-speaker norms. 11 Review of special education plans for school-aged ELs suggest an estimated 40% who were misclassified. For these children, authors write “ special education placement was the ‘early intervention’ when they entered elementary school ”. 12

Despite advances in language research on mono- and bilingual children, comparisons based on age, co-morbidities, and language ability (eg, DLD ± in mono- and bilinguals) may be limited. Regarding age, the first years of life remain critical for language development; 13 thus much research on mono- 14 and bilingual children covers the period prior to school entry, 15 , 16 or just after (ie, up to ≈8 years old). 17 , 18 Children with DLD often have co-occurring difficulties that impact both expression and severity of their clinical and learning needs. During the shift from ‘learning to read’ to ‘reading to learn’ that typically occurs around 9 years of age, 19 reading comprehension problems become more salient. 20 This often leads to a cascading effect of difficulties that arise with language disorders, such as behavioral and social emotional problems, 21 , 22 less social competence, 23 and attention problems. 24 Children with language difficulties report more concerns in the transition from elementary to middle school. 25 From a life course perspective, DLD at school entry is a risk factor for poorer literacy, mental health, and employment outcomes in adulthood. 26 Internationally, rates of compromised language (if not frank DLD) are higher among justice-involved youth vs. community samples, even controlling for socioeconomic status. 27 , 28

Among monolingual children, systematic reviews and meta-analyses of co-occurring difficulties with DLD tend to focus on a specific co-morbidity, such as reading skills, 29 behavioral problems, 21 cognition, 30 or attention. 31 In bilingual children, these reviews have narrowly focused on executive function rather than other cognitive skills, 32 , 33 or comparison of language development in mono- and bilingual children with autism. 34 In addition, studies of bilingualism in older children 35 or those that focus on academic and social emotional development are scarce. In one, a population study of monolingual (DLD+/DLD−) and multilingual (DLD+/DLD−) children, language, literacy, and math performance at follow-up (8–9 years old) tracked closely with DLD status at baseline (4–5 years old), with both mono- and multilingual children with DLD+ performing more poorly. 36

We conducted a scoping review to identify gaps in descriptive (ie, non-interventional) research in school-aged mono- and bilingual children with/without language disorders, across putative comorbid difficulties. The goal was to broadly assess the adequacy of this research, with a focus on the medical literature, to guide future research. The research question guiding our review was: “To what extent does bilingualism research about children with language disorders include children aged 9 years or older, comparator groups by language status (mono- vs bilingual) and ability (with/without language disorder), and data on related difficulties (eg, behavioral)?”.

Protocol and Eligibility Criteria

In contrast to systematic reviews, which are designed to answer more precise questions, scoping reviews “examine the extent, range and nature of research activity” and identify gaps in the literature. 37 , 38 Additionally, scoping reviews provide a better alternative to systematic reviews in cases where researchers are examining how research in a specific content area is conducted – namely, what type of methodological study designs have been used – and can also serve as a precursor to future systematic reviews. 39 In accordance with recent scoping review guidelines, the protocol and eligibility criteria were established a priori 40 and followed Arksey and O’Malley’s (2005) framework, 38 as later enhanced by Levac (2010). 41

• Identify Research Question . See above.
• Identifying Relevant Studies . We applied the following search terms “bilingual” and “language disorders” or “language impairment” and “child[ren].” We conducted the search in PubMed with a date range of August 1, 1979 through October 1, 2018. This search yielded 366 studies, which were entered into a Microsoft Excel dataset. As the review was undertaken to guide a research project, a pragmatic decision was made to search only one database. We focused on PubMed because it indexes: a) American Speech-Hearing-Language Association journals that were of interest, and; b) literature that would include the range of comorbidities of interest.
• Abstract was not in English : studies for which there was not an English translation of the abstract were excluded because the team did not have the linguistic capacity to review.
• Secondary data/review : meta-analyses, literature and systematic reviews, viewpoints, etc., were deemed to lack sufficient detail to complete our charting instrument.
• Special population s: Studies comprised solely of samples selected for specific conditions (eg, children with autism or ADHD) were excluded given a focus on the general population. However, we retained studies in general pediatric samples which, by definition, would include children with such conditions.
• Intervention : Intervention studies tend to focus on a narrow group of eligible treatment subjects. Their inclusion would thus bias results towards under-detecting studies that include this review’s multiple variables of interest, for example, age >= 9 years, measures of co-occurring difficulties). Exceptions include reports of previously conducted interventions with sufficient descriptive data, not otherwise excluded.
• Case study/case series : articles with fewer than 5 participants were excluded, given their limited generalizability.

Title of article, with hyper-link for review by abstracters

• Year–of publication.
• Authors–year and country of authors’ affiliated institutions.
• Language(s)–of children in study.
• Study Groups–were classified based on the authors’ description as: a) Monolingual + Typical Language, b) Monolingual + DLD, c) Bi-/Multilingual + Typical Language, and d) Bi-/Multilingual + DLD. Children (groups) were defined as monolingual, bilingual, or multilingual based on the authors’ designation. Designation of children (groups) as bi/multilingual need not require a specific measure. Children (groups) defined as DLD include those described as having language delay, language disorder, and language impairment.
• Sample size–child participants only; excludes 18+.
• Ages–of children included.
• Language included a broad range of expressive and receptive measures, as well as measures of phonology and narrative language. Not all measures were standardized. Only a few studies examined articulation, fluency, or voice (in addition to other language measures).
• Attention included explicit description of tests of visual and auditory attention, sustained/divided attention (eg, Continuous Performance Test), and behavioral survey measures such as those used to identify ADHD (eg, Conner’s Comprehensive Behavioral Rating Scale).
• Auditory Processing included measures of listening difficulties in the absence of hearing loss. We relied on authors explicit use of this term to identify these measures (eg, dichotic digits, binaural integration).
• Nonverbal Intelligence included measures that assess the ability to think about and solve problems that do not require verbal language, for example, puzzles, pattern recognition (eg, Raven’s Progressive Matrices). Note, we did not classify use of nonverbal intelligence measures to determine study eligibility or for stratification purposes as a study outcome.
• Nonverbal Working Memory : Refers to the ability to temporarily hold and manipulate visual, spatial, and auditory input, (eg, n-bask tasks; verbal memory span).
• Executive Function (EF): Iincluded measures denoted by the authors as tests of executive function (eg, Comprehensive Executive Function Inventory, Wisconsin Card Sorting Test). We are cognizant of the broad conceptualizations of EF, often described as an umbrella of neurocognitive skills (eg, planning, organization, inhibition, shifting, and self-regulation). Included among these are attention and (cognitive) nonverbal working memory, which we identified as separate categories, when they were not explicitly referred to by the authors as tests of EF.
• Reading/Phonology : Included specific mention of reading comprehension task or phonological assessment (in abstract, list of assessments, or title), including sentence/reading comprehension, and phonological repetition, nonword repetition or phonemic awareness tasks.
• Collating, Summarizing, and Reporting Results : If authorship spanned multiple countries, the lead author’s country was listed. Language was dichotomized as “English + Spanish” vs. others because we intended to apply findings to research in the United States, where Spanish is the most frequent second language (L2). Age was classified as including children: younger than 9 years, older than 9 years, or 0 to 18 years. The initial reviewer, who composed screening guidelines, screened all 366 publications and recorded results in Excel. Publications were then divided for secondary reviews to the five co-authors, who were masked to the evaluation of the initial reviewer. Four reviewers screened 73 articles and one reviewer screened 74 articles. The initial reviewer cross-checked all secondary reviewer logs, and those with discrepancies were sent to a seventh reviewer to resolve conflict. Data charting forms for above measures were completed only for publications that met inclusion criteria. Frequencies are presented as number (%). For sample size we present the range, mean (standard deviation) and median (interquartile range). Data were exported to SPSS (IBM Statistics, Version 2.5, 2017) for cross-tabulation analysis by age. We completed the scoping review in October of 2018. Since this time, additional papers have been published. A cursory check of PubMed revealed an additional 57 papers up to June 2020. This value is consistent with the expanding number of relevant papers.

Selection of Sources of Evidence. A schematic of our scoping review’s 5-step methodological framework is shown in Figure 1 . 41 Sources of evidence were selected by a PubMed search for the terms “bilingual”, “children”, and “language disorder” or “language impairment” between the years of 1979–2018. Of the 366 papers initially identified, 207 were excluded because they were: not written in English (n = 27), not primary sources of research (ie, literature reviews, meta-analyses) (n = 67), were primarily focused on interventions (n = 41) or special populations other than children with language disorders (n = 29), and case studies (n = 41). Two papers were excluded under the ‘Other’ category.

Flow diagram.

Characteristic of Sources of Evidence. The remining 159 papers included in the review are listed in the Appendix along with the countries where they were conducted, languages studied, and sample size. Just 4 were published prior to 2000, after which time the number of papers increased by approximately twofold every 5 years, with the last 5-year block showing 72 papers. ( Fig. 2 ) Approximately half were conducted in the United States (n = 83, 52%); countries contributing <3% of studies are not shown. About half included bilingual English-Spanish speakers (n = 82, 52%), with the remainder including other language combinations. The studies’ median sample size was 62 (IQR = 33–119), with the range spanning 9 to 1,108. ( Table 1 )

Number of publications meeting scoping review criteria.

Overall Data Frequencies (n = 159 Studies)

TLD indicates typical language development.

• Results of Individual Sources of Evidence: N/A: only one source. See below for summary of results.
• Synthesis of results: While most studies included bilingual children with typical language (n = 138, 87%), just half included bilingual children with DLD (n = 86, 54%), and few included all 4 study groups (n = 22, 14%). Among studies with a Bilingual DLD group, the majority included a Bilingual TLD group (70/86, 81%). Similarly, among the studies with a Monolingual DLD group, most included a Monolingual TLD group (30/39; 77%) [not shown]. Just over one-quarter included any children aged 9 years or older. As expected, most included language measures (n = 145, 91%). Just under a third assessed reading/phonology (n = 51, 32%) or nonverbal intelligence (n = 49, 31%). The remaining measures were included in fewer than 10% of studies. ( Table 1 )

Data stratified by age < or >= 9 years of age are shown in Table 2 . Age data were missing for 2 studies, thus the denominator used to calculate cell percentages is n = 157. Less than a third of studies included any children 9 to 18 years (n = 48, 31%); 5 studies (3%) included only children of this age. Among the 48 studies with any 9 to 18 year olds, just 4 (8%, 4/48) included all 4 language groups. Despite increased executive function and reading demands around 9 years of age, relatively few studies of older children include these measures.

Frequency Data by Age (n = 157)

DLD indicates developmental language disorder.

Typical = typical language.

Most children with DLDs have difficulties that persist into later childhood; prolonged difficulties impact literacy development. Paradoxically, the scope of research on DLD and related skills in school-aged mono- and bilingual children remains unclear. This scoping review examined the extent to which bilingualism research about children with language disorders includes children aged 9 years or older, comparator groups by language status (mono- vs bilingual) and ability (with/without language disorder), and data on related difficulties. Of the 159 manuscripts that met inclusion criteria, just 31% included any 9 to 18 year-olds, and only 3% included only 9 to 18 year-olds. Just 14% included all four language groups, and apart from nonverbal intelligence (31% of studies) or reading (32% of studies), few included data for related difficulties.

Research on bilingual children with DLD was largely absent prior to 2000, but increased sharply between 2010 and 2018. Slightly over half the studies examined Spanish-English bilinguals – likely because many were from the United States, where Spanish is the most commonly spoken second language. Among the 60 million persons in the United States older than 5 years who speak a language other than English at home, more than half speak Spanish or Spanish Creole (37.5 million), followed by Chinese (2.9 million). 42 Worldwide, two-thirds of people speak one of 12 languages, the top 5 of which were: Chinese (all dialects, 1.4 billion), Hindu-Urdu (588 million), English (527 million), Arabic (467 million), and Spanish (389 million). English is spoken in the greatest number of countries (101). 43 Yet, few studies identified for our scoping review included speakers of Arabic or Hindu-Urdu. Thus, our research suggests that research on both DLD and typical language development be expanded to these languages.

There was a dearth of studies in all 4 comparator groups. Few studies compared all 4 language groups (bilingual typical, monolingual typical, bilingual DLD and monolingual DLD). The (relatively) more limited research on mono- versus bilingual children with DLD may impede understanding of what DLD ‘looks like’ in mono- versus bilingual children. As well, we found limited assessment of related difficulties. This finding runs counter to the shift in terminology from SLI to ‘DLD,’ which better approximates DLD’s co-occurrence with other neurodevelopmental disorders, 3 and its clinical presentation. For example, our multidisciplinary developmental disabilities center’s school-age unit in the Bronx, New York evaluates children 6 years or older in 2019. Excluding those with autism and intellectual disability, n = 168 were diagnosed with DLD, including a third who were bilingual English-Spanish. Among these children with DLD, 91% had one or more academic, behavioral, or emotional difficulty including: reading (44%), math (38%), writing (34%), ADHD (53%), anxiety (27%), or depression (9%). These (unpublished) clinical data support the conceptualization of DLD as a spectrum disorder, as others have. 44 Our findings thus suggest that DLD research has not kept pace with the conceptualization and presentation of DLD.

The first US profile of middle childhood health and behavior found that more than 20% of 6 to 11 year-olds had a special health care need (including behavioral or developmental) and that speech-language disorders peaked at 7.7% at 8 to 9 years. 45 Yet, a majority of studies in our scoping review (70%) were in children younger than 9 years; just 5 studies (3%) included only these older children. With mounting cognitive, regulation and social demands in early preadolescence, persistent language deficits can lead to a child being newly diagnosed with a reading or learning disability. Late detection of reading disorders in particular occurs in ELs and children with lower socioeconomic means. 46 Additionally, Black, Hispanic, and linguistic minority children in the United States are less likely to be identified with a learning disability or speech-language impairment by the end of middle school than similarly situated white peers. 47 Our clinical experience echoes this finding: among children newly diagnosed with DLD at our center’s school-aged unit (see above), 75% were 9 years or older. Our center is located in the Bronx, where nearly 60% of households speak a language other than English, and 27% of persons meet US Census criteria for poverty, 48 underscoring the disparities related to timely identification of DLD.

This scoping review possesses both strengths and limitations. To our knowledge, this is the first scoping (or systematic) review to concomitantly examine language differences (eg, mono- vs bilingual) and disorders, age and related difficulties. Other strengths include adherence to established scoping review protocols, masked secondary review of initial charting decisions, and a multidisciplinary reviewer team that included clinical, language disorders, and neuroscience expertise.

A primary limitation of this review is its reliance on PubMed alone, rather than additional education or psychology databases. The authors undertook this review to inform their development of a research project; in this context use of a single database was deemed practical and appropriate. We selected PubMed given our focus on identifying difficulties that often co-occur with DLD but that go beyond language as well as because PubMed indexes American Speech-Language-Hearing Association (ASHA) journals. To gauge the extent of this limitation, we conducted a cursory review of ERIC (EBSCO) (sponsored by the US Department of Education) using the same initial search terms and time period. This yielded n = 108 papers (vs n = 366 in our review), 55% of which were indexed in PubMed. Titles ‘missed’ from PubMed included those in linguistics and bilingualism journals which might have rendered our findings on comorbidities even more conservative. Conversely, the search in ERIC missed 62% of papers identified in PubMed, including those in International Journal of Speech-Language Pathology, American Journal of Speech-Language Pathology, Clinical Linguistics and Phonetics, and the Journal of Communication Disorders. At the same time, this cursory review identified a parallel increase in research on bilingualism in the past decade across both search engines. Findings reported here can serve as a precursor for a more comprehensive (using multiple search engines), systematic review of this topic. Additionally, omitting ‘adolescent’ as a search terms may have missed a small number of papers.

CONCLUSIONS

Our scoping review identified substantial gaps in research on bilingualism in children in terms of related difficulties, comparator groups, and age. In the United States, where speech-language pathologists must adhere to both ASHA and Individuals with Disabilities Education Act requirements, there has been progress in evaluating language proficiency in bilingual speakers. 49 However, the relatively more limited research on both mono- and bilingual children with DLD presents limitations to this progress. Worldwide, there is some misalignment between languages studied compared with the number of speakers of major language groups. Future research that captures the breadth of DLD as a spectrum disorder, across childhood, is warranted.

What this Systematic Review Adds:

• Developmental language disorder (DLD) may go undetected until children start ‘reading to learn’.
• DLD can be difficult to diagnose in bilingual speakers, especially absent comparative data on mono- and bilingual children with/without DLD.
• Research is needed on school-age comparator groups.

How to Use this Systematic Review:

• For pediatricians in diverse settings: to guide clinical data collection in mono- and bilingual children and DLD.
• To guide analysis of secondary data in mono- and bilingual children and DLD.
• To advocate for increased DLD screening in school-aged mono- and bilingual children.

Supplementary Material

Appendix table, acknowledgments.

The authors would like to thank Ms. Emma Brezel for data entry assistance.

Financial statement:

This work was supported by a grant from the US Department of Health and Human Services, Administration on Community Livings (90DDUC0035), core funding grant for the Rose F Kennedy University Center of Excellence in Developmental Disabilities.

The authors have no conflicts of interests to report.

Supplementary Data

Supplementary data related to this article can be found online at https://doi.org/10.1016/j.acap.2021.12.002 .