Cognitive advantages of bilingualism

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Being bilingual has been linked to a number of cognitive benefits. Research has studied how a bilingual individual's L1 first language (L1) and second language (L2) interact, and has shown that both languages have an influence on the function of one another, and possibly on cognitive function outside of language. Some research on linguistic development, perception, and attentional and inhibitory control has suggested that bilinguals can benefit from significant cognitive advantages over monolingual peers in various settings.

However, there is some disagreement over how these findings should be interpreted. A systematic review of studies carried out between 1999 and 2012 found that the evidence for cognitive advantages is mixed and that reporting may be subject to publication bias which has given a distorted view of the evidence.[1]

During the history of research into the cognitive advantages of bilingualism, the view shifted from a subtractive to an additive perspective;[2] that is from believing that being bilingual detracts from one's abilities to believing that being bilingual adds to an individual's abilities.

A bilingual can be defined as an individual that is exposed to two languages simultaneously from a young age (under 3),[3]although the definition may vary slightly depending on the studies being presented and their sample selection processes. Several definitions have been given in the literature for bilingualism, for example, either individuals that are learners of another language irrespective of proficiency, or individuals that are equally proficient in both languages.


Before the 1960s research on bilingual individuals was varied but with a specific pattern of conclusions, namely that being bilingual was detrimental to a child's linguistic and cognitive development, and put the individual at a disadvantage compared to monolingual peers. The general opinion was that bilinguals would have smaller vocabularies, stunted general cognitive abilities and that children learning two languages from a young age would be spending too much of their energy differentiating and building the two languages to become competent in either one.[4][5] Studies referred to the "problem of bilingualism" the "handicapping influence of bilingualism"[6] and reported that bilinguals performed worse in IQ tests, had smaller vocabularies, and suffered in most aspects of language development, as revealed mostly through verbal IQ tests.[5][7]

However, these studies suffered from several methodological problems that undermined the soundness of their conclusions. They employed unstandardized and subjective definitions of bilingualism and of a bilingual individual (e.g., labeling a person as bilingual or monolingual through assumptions based on the national origin of that person's parents or even based on that person's family name), raising the concern that there is no way of determining whether their samples were truly representative of a bilingual population; they did not control for socioeconomic status (SES); and many of them administered verbal-intelligence tests to non-proficient speakers of a second language in that second language.[7][8]

In 1962, Peal and Lambert published a study which brought to light the importance of controlling for such factors as age, sex, and SES, as well as of having a standardised measure for bilingualism, when selecting a sample of bilinguals to be studied. In their study where they carefully matched their bilingual to their monolingual participants, they found that the bilinguals showed significant advantages over the monolinguals in both verbal and non-verbal tests, especially in non-verbal tests that required more mental flexibility.[9]

Since then, the literature has consistently found advantages of bilinguals over matched monolingual peers in several aspects of language development and ability, as well as in more general areas of aptitude such as perception and executive functioning.


Leopold, in his record of his daughter's bilingual development of language[10] observed that she had "loose connections" between the (phonetic) structure of words and their semantics (meaning), demonstrated by her frequent substitution of English words with German and vice versa, in every day speech and even well rehearsed songs and rhymes. He notes that this gave her a greater flexibility in the use, and a way of use of language, that was unobserved in monolingual children of her age, and that perhaps this loose connection between the meaning and form of a word could result in more abstract thinking or greater mental flexibility.

In 1972, Worrall[11] designed a study to test Leopold's[10] observations and was able to replicate them. She tested two groups of monolingual and bilingual children at ages 4–6 and 6–9, and presented them with tests to assess whether they showed a semantic or phonetic preference when categorising words. An example of one task given in the paper was to decide which of the two words can and hat were more similar to the word cap. The semantic choice would be hat, versus the phonetic which would be can. Other tests were designed to provide a choice between semantic and phonetic interpretation of objects (e.g. in a hypothetical situation could you call a cow a dog and if you did would this dog bark?).

She found that, although both monolingual and bilingual children showed no differences in the way they understood the words used, 54% of the younger bilingual children consistently showed a semantic preference in contrast to their monolingual peers. In monolingual children, semantic preference increased with age, suggesting that bilingual children reach a stage of semantic development 2–3 years earlier than their monolingual peers. This finding is in stark contrast to the early research and claims about bilingualism which warned that bilingualism stunts children's linguistic development.

In their book In Other Words,[12] Ellen Bialystok and Kenji Hakuta examine the idea that "the knowledge of two languages is greater than the sum of its parts." They argue that the linguistic benefits of being bilingual are more than simply being able to speak two languages. If a child is learning two languages whose structures and rules are significantly different from each other, this would require the child to think in more complicated ways. An example of this is the understanding of the arbitrariness of labels for objects discussed in the above paragraph, but also being able to distinguish between and use two different grammatical or syntactical structures. This enables the child to increase their understanding of the structure of language and gain a greater awareness of meaning; an increase of metalinguistic awareness.[2][13][14]

Bialystok argues that metalinguistic awareness also increases bilinguals' control of linguistic processes, such as having a greater ability to detect grammatical or syntactical errors, and recognize words in continuous speech.[15] Bilinguals have also been found to outperform monolinguals in reading ability (an effect modulated by the relationship of the two languages),[16] and better reading skills in L1 were demonstrated with as little as an hour a week of L2 learning,[17] suggesting that being bilingual is also advantageous in the development of reading as well as spoken language.

Metalinguistic awareness has therefore been shown to benefit the individual in the acquisition and use of language, giving bilingual individuals (who acquire metalinguistic awareness earlier in life than their monolingual peers) a firm advantage. However, it has also been proposed that metalinguistic awareness could result in advantages in other cognitive abilities besides language, giving individuals a generalised cognitive advantage over monolinguals (see below).[4][5][12]

Finally, studies have shown that regardless of the language in use at a present time, both languages are constantly active both phonologically and semantically in bilingual individuals, as indicated by electrophysiological measures of performance, even though behavioural measures such as reaction times often do not indicate such an interference.[18][19][20][21]

In 2011, Wu and Thierry[19] conducted a study where bilinguals were shown picture pairs and asked to judge whether the word pairs corresponding to the pictured objects rhymed or not. Word pairs were designed so that they either rhymed in both L1 and L2 or only in one of the two languages. Electrophysiological measures (see Event-related potential) of the effect (priming) of the sound repetition induced by the rhyming of the word pairs, showed that even though the participants were performing the task in L2, they showed a priming effect (albeit delayed) when those L2 words rhymed in L1.

In 2012, Hoshino and Thierry[18] conducted a study where participants were shown word pairs in L2 that sometimes contained words that were cognates to L1 words. Participants judged whether the words in the pairs were related, and electrophysiological results revealed that semantic priming (facilitation of processing of the words) occurred when the words in the pairs were related to each other whether or not the meaning was interpreted in L1 or L2.

Both these studies conclude that both languages of an individual are constantly unconsciously active and interfering with one another with facilitatory results regarding the processing of words, explaining bilinguals' advantages over their monolingual peers when it comes to linguistic processing.

Effects on vocabulary[edit]

It is a well-replicated finding that bilinguals have a smaller vocabulary size than their monolinguals counterparts.[22][23][24][25][26] Given that bilinguals accumulate vocabulary from both their languages, when taking both languages into account, they have a much larger vocabulary than monolinguals. However, within each language bilinguals have a smaller vocabulary size and take longer to name pictures as seen in standardized vocabulary tests e.g. Peabody Picture Vocabulary Test and Boston Naming task. A possible explanation may be; it is well known that the frequency of use of words is related to increased lexical accessibility; words that are used more frequently are accessed more quickly.[26][27][28] Therefore, bilinguals may be 'less proficient' relative to monolinguals, purely because they use one sole language less frequently than monolinguals, who use the same language all the time. In addition, the need to select the appropriate language system makes ordinary linguistic processing more effortful; the simple act of retrieving a common word is more effortful for bilinguals than monolinguals due to the competition of the two languages.[26]

Effects on L1 from prolonged exposure to L2[edit]

It has been suggested that prolonged naturalistic exposure to L2 affects how L2 is processed, but also may even affect how L1 is processed. For example, in immersion contexts (where the individual is in an environment where L2 is used), the individual experiences reduced access to L1 and extensive contact with L2, which affects and facilitates processing of L2.[29][30] However, this may also consequently affect processing of their L1 e.g. increased difficulty in naming objects and phonology.[31][32] Bilinguals are not two monolinguals in one brain and even the supposedly 'stable' L1 system is open to influence once individuals become proficient in the L2.[24][33][34][35] If the frequency to L2 affects the language processing in L1, then bilinguals in the L1 environment should process sentences differently than similar bilinguals in the L2 environment. For example, a Spanish-dominant bilingual in Spain may process sentences differently than a Spanish-dominant bilingual in England.

To test this hypothesis, Dussias & Sagarra (2007)[36] investigated how individuals in these two environments interpreted temporarily ambiguous phrases e.g. Alguien disparó al hijo de la actriz que estaba en el balcón!/ 'Someone shot the son of the actress who was on the balcony'. When asked the question, Quien estaba en el balcón?/ Who was on the balcony?', monolingual Spanish speakers will typically answer 'the son' as they have a high attachment preference (they attach the modifier to the 'higher' verb phrase [shot the son]). Whereas, monolingual English speakers will answer 'the actress' as they have a low attachment preference (they attach the modifier to the 'lower' verb phrase [the actress who was on the balcony]).[35][37] Confirming the hypothesis, Duissas & Sagarra (2007)[36] found that Spanish-English bilinguals in a Spanish-speaking environment showed preference for the typical Spanish high-attachment strategy and Spanish-English bilinguals in an English-speaking environment showed preference for the typical English low-attachment strategy, even when reading the phrase in Spanish (their dominant language). This may be because they have more exposure to English constructions, so this may be more available to them.[35]

Parallel activation of both languages in bilinguals[edit]

It has been found that a bilingual's two languages are simultaneously active during language use.[35][38] It makes sense that a person's dominant language (L1) is active when using the less dominant language (L2), however, it is striking that L2 is also activated when using L1. This happens once the individual is adequately proficient in the L2.[39] They are both active when listening to speech, reading words in either language or even planning speech in either language.[35][40][41][42] Also surprisingly, both languages are activated even when only language is needed by the user.[42][43] Bilingualism studies have mostly looked at Spanish-English or Dutch-English bilinguals. All these share the Roman alphabet, where there are many cognates (words which have the same linguistic deviation e.g. 'piano' is the same in all 3 languages. Cross-language activation therefore seems more plausible. However, cross-language activation has also been reported in bilinguals where their two languages have different script (alphabet) and lexical form e.g. Chinese and English. A study by Hoshino & Kroll (2008)[44] demonstrated that Japanese-English and Spanish-English bilinguals performed similarly in picture naming tasks even though the cognate names of words for Spanish-English bilinguals shared phonological and orthographic (spelling and letters) information whereas the Chinese cognate names were only phonologically similar. Although the words were spelt and presented differently for Chinese-English bilinguals, this did not affect the simultaneous activation of both their languages.

On the other hand, the fact that both languages are constantly activated means that they potentially compete for cognitive resources; bilinguals need to acquire a way to control or regulate the competition, so as to not use the wrong language at the wrong time or equally, not lose fluency in each language. It has been demonstrated that bilinguals show better executive control than monolinguals matched in age and other background factors (e.g. social-economic status).[45][46][47][48] Executive control supports activities such as high-level thought, multi-tasking, sustained attention, working memory and inhibition.[49] Inhibition refers to being able to ignore irrelevant information and therefore not be distracted by non-target stimuli. For example, a test that is widely used to assess this executive function is the Stroop task, where the word of a colour is printed in a different colour to the name (e.g. the word 'red' printed in blue ink). This causes interference and distraction; reaction times are measured to see how distracted the individual is by the incongruent word and colour. Bilinguals compared to monolinguals have shown an advantage at this task, suggesting that bilinguals have a more developed inhibition process, due to the constant inhibition of their non-target language.[46][48][50]

Inhibition has been suggested as the executive control system that allows successful linguistic selection even when both languages are co-activated in bilinguals. De Groot & Christofells[51](2006) proposed a distinction between two types of inhibition that may occur; global inhibition and local inhibition. Global inhibition refers to suppression of an entire language system, e.g. inhibiting Spanish when speaking English, and local inhibition refers to inhibition of a more specific competing vocabulary, e.g. the translation of the same word or phrase. Local inhibition mostly affects linguistic performance whereas global inhibition affects both linguistic and cognitive performance. Linguistic outcomes of inhibition are reduced speech and fluency of lexical access for bilinguals.[52]

Executive functions[edit]

Executive functions are those cognitive processes such as problem solving, mental flexibility, attentional control, inhibitory control, and task switching. Bilingual individuals have been shown over a number of different tasks and situations to be better at such processes; suggesting an interaction between being bilingual and executive functions.[14]

Hakuta and Diaz,[5] addressed the chicken and egg question concerning bilinguals and their enhanced cognitive abilities; do children with greater cognitive abilities tend to learn more than one language, or is it knowing more than one language that enhances cognitive ability? They administered a set of non-verbal tests that are designed to measure cognitive ability (Raven's Progressive Matrices) to a bilingual sample of children. They found a high correlation with the degree of bilingualism (how proficient the individuals were in each of their languages) of their sample and scores on the test, as well as bilingualism did in fact predict performance (and therefore cognitive ability). However, an important point to note, is that most native bilinguals haven't learnt a second language because they are more intelligent. In most cases, they have grown up in a family where use of the two languages is necessary and therefore it is unlikely that the child's intelligence will allow them to learn the second language.

Bialystok makes a distinction between two types of processing that aid children in language development; analysis, which involves the ability to represent and understand abstract information, and control, which involves the ability to selectively attend to specific aspects of structures whilst ignoring irrelevant information.[53] The literature concludes that it is in the aspect of control that bilinguals have been found to have an advantage over their monolingual peers when it comes to cognitive abilities.

In one study,[54] Bialystok administered a non-linguistic card-sorting task to her participants that required flexibility in problem solving, inhibiting irrelevant information, as well as recognizing the constancy of certain variables in the face of changes in the rules. She found that bilingual children significantly outperformed their monolingual peers in this task, suggesting early development of inhibitory function that aids solving problems that require the ability to selectively focus attention.

In a following study, Bialystok and Martin[55] aimed to determine what gave bilinguals an advantage in solving the card-sorting task (and generally an advantage in problem solving situations). Though the groups were equivalent in their ability to represent the stimuli (reflecting back to Worrall's findings[11]), and both were equally able to inhibit learned motor responses, bilinguals showed a firm advantage in the task requiring conceptual inhibition; the ability to inhibit previous associations and create new mental representations of the stimulus according to task changes.

An explanation offered by Bialystok[55] and others[56] for this greater ability of bilinguals to selectively attend to important conceptual attributes of a stimulus, is that it may stem from the bilinguals' constant need to inhibit competing labels in their two languages for one object according to the currently relevant language. Bilinguals have different representations in each language for similar concepts and therefore need to constantly be aware of which language they are using and which the appropriate word is to be used in that context. This culminates in an advantage of cognitive control, since the ability to switch between languages and select the appropriate word for use is directly linked to the ability to better attend to relevant, or inhibit irrelevant, information.[57] A further explanation refers to bilinguals' unique experience with using two languages in the same modality (spoken), differentiating them from monolingual peers, and requiring them to make the decision about how best to respond to a situation, as well as have better control over what they select.[58]

Ellen Bialystok has done extensive research[16][54][55] into the cognitive advantages of bilingualism. In several studies she has shown that bilinguals outperformed their peers in tasks measuring executive function, suggesting that being bilingual gives the individual an advantage of better control of attention and therefore facilitates processing and functioning in several cognitive tasks. Moreover, the ability to better attend to or inhibit irrelevant information has been found to persist into adulthood with bilingual adults (that have been bilingual since childhood) who show better controlled processing than monolingual peers,[59] and has even been linked to slowing age-related cognitive decline.[60]

Benefits in older adults[edit]

There has been a surge in interest in the benefits of bilingualism against age-related cognitive decline.[45] Klein & Viswanathan[45] found that the normal decrease in attentional control observed in older adults was reduced in bilinguals, suggesting that bilingualism may be protective against the effects of cognitive ageing. Elderly bilinguals have also been shown to be better at switching between tasks, ignoring irrelevant information and resolving conflicting cognitive alternatives.[61] Bilingualism may be one of the environmental factors which contributes to 'cognitive reserve'.[62] Cognitive reserve is the idea that engagement in stimulating physical or mental activity can act to maintain cognitive functioning in healthy aging and postpone the onset of symptoms in those suffering from dementia.[63] Factors that contribute to this also include education, occupational status, higher socio-economic class, and the continuing involvement in physical, intellectual and social activities.[64][65][66]

To test the protection against Alzheimer's disease (AD), Bialystok et al. (2007)[60] examined the hospital records of monolingual and bilingual patients who had been diagnosed with various types of dementia and they found that bilinguals experienced the onset of symptoms and were diagnosed approximately 3–4 years later than monolinguals (controlled for various cognitive and other factors). This was replicated with patients all diagnosed with AD.[67] It is important to stress however that bilingualism doesn't directly prevent one from having AD, but enables functional cognition for a longer period of time; it delays the onset of symptoms for those with the disease. This was confirmed by the finding that, when monolingual and bilingual Alzheimer's patients' brains were scanned, bilinguals actually had more pathology (disease) and damage than the monolingual patients.[68] This suggests that active use of the two languages protects against the symptoms of the disease; areas of the brain that enable cognitive control may have benefitted from the bilingual experience and so improve cognitive function in older age. This finding has also been replicated by several other studies [69] Bilingualism is thought to develop cognitive control skills, and other factors also contribute to this in life, for example, becoming a skilled musician, playing video games, driving a taxi through a maze of city streets.[35] However, the benefit of bilingualism over these is that language is used much more frequently than any of these activities and thus provides the most benefit.

Age-related differences[edit]

The bilingual advantage in cognitive function has been demonstrated especially in children and older adults, however the advantage in young adults has been rather variable.[48][70] Suggestions for this finding may be that young adults are at their peak cognitive function, so it may be difficult to show any bilingual advantages beyond that peak level, especially in simple executive function tasks[35][48]). However, larger advantages have been seen in children, and especially in older adults.[45][46][71] It is thought that the benefits may be particularly beneficial to individuals at points in their lives when they are more vulnerable, for example in early development[72] and later in life, when ordinary cognitive processes decline.

Age of second language (L2) acquisition[edit]

A large debate is whether the age of acquiring L2 has effects on the bilingual advantages.[69] A study on native bilingual vs late bilingual vs monolingual children in the USA revealed an overall bilingual advantage.[26][73] However, native bilingual children demonstrated better performance on a selection of executive function tasks compared with their late bilingual and monolingual counterparts. Participants were controlled for age, verbal ability and social-economic status (parent education level). However, there are various methodological outcomes which may question the validity of these results. Firstly, a small sample size was used, with only 12 children in the bilingual group, 21 in the immersion group (late bilingual) and 17 in the monolingual group. 'Late bilingual' in this study was classified as a monolingual child who had been in a bilingual school for 6 months (where half the lessons were in English and half in Spanish/Japanese). This may be a poor representation of 'late bilinguals' as 6 months may not be enough time for cognitive changes and adaptations to the brain to have taken place, and these children will unlikely be 'proficient' in the L2, therefore this is not an appropriate group sample to support the claims being made. In addition, the effect sizes on all the individual executive function tests were all small to moderate effect sizes (ƞ2= 0.01à 0.2). In combination with the lack of power due to small sample size, strong conclusions cannot be drawn from this data.

However, L2 acquisition as an adult is associated with variable mastery of the language and incomplete acquisition, especially in the sound system and grammatical structures.[32][74][75][76][77] Bilinguals who learn their second language in adulthood will not be able to master the language as effectively as a native bilingual. Some researchers have argued that access to all the potential linguistic structures required for successful L2 acquisition is not available after the so-called critical period, which roughly coincides with the onset of puberty.[35] The absence of the relevant structures in the L1 presents an obstacle to achieving complete acquisition of the second language.[75][78][79]

Other researchers claim that, although the age of acquisition may have profound influences on some aspects of processing L2 and structural organization of the neural networks that support language,[35][80][81] recent studies have suggested that language proficiency may be more important in determining cross-language interactions.[82][83]

Despite all of the research, there is still not a widely accepted answer. Currently, it is known that early age of acquisition, overall fluency, frequency of use, levels of literacy and grammatical accuracy all contribute to the bilingual advantage, with no single factor being decisive.[63][84] All these factors, with unknown individual importance, contribute to complete acquisition of a second language.


A review of the literature suggests that bilingualism has an additive effect on an individual's creativity, by enhancing their mental flexibility, their ability to solve problems, and to perceive situations in different ways and the ability to maintain or manipulate these perceptions to suit the task at hand, all in ways that matched monolingual peers do not exhibit.[11][12][14]

One study addressed a less explored field of cognitive advantages bilingual children may exhibit, in the use of creativity to solve of mathematical problems.[85] Participants were presented with problems that were either mathematical in nature (arranging two sets of bottle caps to be equal according to instruction) or non-mathematical (a common household problem represented in pictures) and were asked to provide solutions, while being rated on scales of creativity, flexibility and originality. The results of the study confirmed that the bilingual children were more creative in their problem solving than their monolingual peers. One attribution for this trait could be bilinguals' increased metalinguistic awareness, which creates a form of thinking that is more open and objective, resulting in increased awareness and flexibility.

This enhanced mental flexibility that develops in bilinguals influences more than their problem solving or linguistic skills. Language appears to change the way the world is perceived between individuals that speak different languages, and it has been shown to influence the perception of color[86] as well as the categorisation of objects.[87]

Thierry et al.[86] studied how having different words for different colors in one language might affect the perception of that color as compared to a language that does not discriminate between those colors. In Greek, "light blue" is distinguished from "blue", not simply as a different shade but as a whole different category of color. In this study, bilingual and monolingual Greek/English participants were shown different shades of blue and light blue as well as green and light green (for which a distinction is not made in Greek) and ERPs were recorded. Electrophysiological measures showed a distinct pattern for the bilinguals indicating that they were perceiving the two colors as completely separate.

Cook et al. explored the fact that Japanese speakers are more likely than English ones to categorize objects according to their material as opposed to their shape. In their study,[87] they found that the preferences of Japanese monolinguals learning English changed; the more proficient they became in English, the more their object categorization results matched those of English monolinguals.

See also[edit]


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