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Executive Function
Executive function is the domain of high-level cognitive processes that assist in goal-oriented tasks, such as problem solving, mental flexibility, attentional control, inhibitory control, and task switching. A great deal of research has been committed to investigating a potential connection between bilingualism and enhanced executive function. Many researchers have asserted that bilinguals show better executive control than monolinguals matched in age and other background factors (e.g. social-economic status), suggesting an interaction between being bilingual and demonstrating honed executive functions.[14][49][45][46][47][48]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 (see age-related effects section below).[60]

In support of a connection:
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.

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 which 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 Worrall's findings, described below[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.

Possible explanations
Green offered an explanation for this phenomenon with her "inhibitory control model." Proposed in 1998, this model references a bilingual's constant need to suppress one language while using another. Because this task requires suppressing a source of distraction, this kind of control is then applied to other tasks. This assertion was bolstered by a study of unimodal bilinguals (bilinguals who communicated with two spoken languages) and bimodal bilinguals (bilinguals who used one spoken language and sign languaginguals who did not frequently switch did not. However, this study did not control for similarity between the languages (languages that are more similar might require more attention to keep straight). When Verreyt, Woumans, Vandelanotte, Szmalec, and Duyck ran a similar study but with all participants having the same languages, they replicated the results of Prior and Gallan. Additionally, because their study looked at tasks measuring inhibition even though language switching should directly affect switching tasks, they argued that the effects of language-switching carry over multiple facets of executive control.

Bialystok[55] and others[56] have echoed this idea that the greater ability of bilinguals to selectively attend to important conceptual attributes of a stimulus 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 what 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]

Is bilingualism or executive control the causative force?
Hakuta and Diaz 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.

Against a connection
Not all researchers agree that bilingualism contributes to enhanced executive function.

Some take issue with methodology. Virginal Valian asserts that the correlations between bilingualism and executive function are inconsistent, largely due to the fact that different tasks contribute to executive function. Because some of these tasks are available to monolinguals and bilinguals may similarly participate in these tasks to varying degrees, she argues that bilinguals cannot be assumed superior to monolinguals in executive function. She also cites that bilinguals are not consistently better at all executive function tasks.

ing. They assess their sample as similar in confounding variables and found that not only was there not evidence supporting an advantage for bilinguals, but that if anything, the evidence would argue against this.

'''MB comment: here too, I can't see what is different from the original except that you deleted a paragraph. Is that the only change?'''

Metalinguistic Abilities
Bilingual individuals have also shown superiority in metalinguistic ability. This additional advantage seems closely tied to executive function. Metalinguistic awareness is the understanding of the separation between language’s structure and its meaning. For example, being able to judge the grammaticality of a sentence regardless of whether it is sensical, or being able to separate the set of sounds comprising a word from the word’s meaning. The ability to suppress distracting information, such as semantics, is an act of inhibition, meaning that it falls into executive function. This ability could also be exercised by being bilingual, given that a bilingual individual has to suppress their knowledge of another language system when operating in one of their languages (CITE GROSJEAN AND LI PG 202).MB comment: careful: it is okay to cite Grosjean and Li, but they might be citing some other study, since their book is not original research but a summary of the field.

Bialystok also studied metalinguistic abilities in bilinguals versus monolinguals by having subjects judge whether a sentence was grammatical, regardless of its logical sense. Bilinguals outperformed monolinguals in judging that a non-sensical sentence was correct. Additionally, when brainwaves of bilingual adults were observed at during the task, they showed less of a reaction indicative of processing conflict as reflected on the P600 waveform (G & LI pg 196-197).

Studies by Leopold and Worrall investigated bilingual children's awareness of the fact that the connection between words and meaning is arbitrary. See language section below.

MB: same comment here as above re: Grosjean & Li.

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. [5][12]

MB comment: so this seems to be a slight reformulation of the section currently called Language, is that the intention?

Parallel Activation of Both Languages
It has been found that a bilingual's two languages are simultaneously active, both phonologically and semantically, during language use.[35] [38] This activation is indicated by electrophysiological measures of performance. Interestingly, behavioural measures such as reaction times often do not indicate such an interference.[18][19][20][21] Not only is a person's dominant language (L1) active when using the less dominant language (L2), but their 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, both languages are activated even when only one 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, and 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 less surprising. However, cross-language activation has also been reported in bilinguals where their two languages have different script (alphabet) and lexical form (e.g. Japanese 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 Japanese cognate names were only phonologically similar. Although the words were spelt and presented differently for Japanese-English bilinguals, this did not affect the simultaneous activation of both their languages.

In 2011, Wu and Thierry conducted a study where Chinese-English bilinguals were shown picture pairs. Participants were asked to name the second picture in the pair when it was shown and then were 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. This suggested that in regards to language use, both L1 and L2 are accessed and compete for selection during L2 production.

In 2012, Hoshino and Thierry[18] conducted a study where Spanish-English bilingual participants were shown word pairs in English, their L2, and asked to judge whether the word pairs were related. Sometimes, things presented would be "interlingual homographs," or words that sound the same in both languages but have a different meaning in each. These pairs would be primed by things relating to one of the meanings or to neither, and the effects of this priming were measured electrophysiologically. 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 the meaning was interpreted in English or Spanish.

The two most immediately preceding studies conclude that both languages of an individual are constantly unconsciously active and interfering with one another. The results, in regard to word processing, can help demonstrate how bilinguals have advantages over their monolingual peers when it comes to this area of study.

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. 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 for a colour is printed in a different colour than 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, potentially 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 less positive than the outcomes for executive function: reduced speech and fluency of lexical access for bilinguals.[52]

'''MB comment: some of this reorganizat! I like that you moved the discussion of the Wu & Thierry and Hoshino & Thierry studies into this section.'''

Age-related benefits
There has been a surge in interest in the benefits of bilingualism against age-related cognitive decline. Klein & Viswanathan found that the normal decrease in attention control observed in older adults was reduced in bilinguals, suggesting that bilingualism may be protective against the effects of cognitive aging. Elderly bilinguals have also been shown to be better at switching between tasks, ignoring irrelevant information and resolving conflicting cognitive alternatives. Bilingualism may be one of the environmental factors which contributes to 'cognitive reserve'. 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. Factors that contribute to this also include education, occupational status, higher socioeconomic class, and the continuing involvement in physical, intellectual and social activities.

To test the protection of bilingualism against Alzheimer's disease (AD), Bialystok et al. (2007) examined the hospital records of monolingual and bilingual patients who had been diagnosed with various types of dementia. After controlling for various cognitive and other factors, found that bilinguals experienced the onset of symptoms and were diagnosed approximately 3–4 years later on average than monolinguals. This was replicated with patients all diagnosed with AD. It is important to stress however that the studies did not show that bilingualism directly prevents one from having AD, but rather 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 (signs of disease) and damage than the monolingual patients. 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 benefited from the bilingual experience and so improve cognitive function in older age.

The finding that bilingualism contributes to cognitive reserve has also been replicated by several other studies For example, Abutalebi et al. (2015) tested 19 bilingual (8 Cantonese-Mandarin and 11 Cantonese-English, age range 55-75) and 19 monolinguals (Italian speakers, age range 49-75) who had been matched for education level, performance on the Flanker Task (a cognitive response test,) and socioeconomic status. It is important to remember that this is a relatively small sample size; however, the results did confirm previous studies. According to the research, the bilinguals outperformed the monolinguals on all experimental tasks, and the researchers found that monolinguals' neural imaging showed higher signs of age-related effects on performance of tasks and decreased gray matter density. Meanwhile, the bilinguals' neural imaging showed higher levels of gray matter along the anterior cingulate cortex. Because of these results, the investigators concluded that bilingualism aids in protection against cognitive decline.

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. 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. 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 and later in life, when ordinary cognitive processes decline.

Age of acquisition
A debate within the linguistic community is whether the age of acquiring one's L2 has effects on the cognitive advantages. A study on native bilingual vs late bilingual vs monolingual children in the USA revealed an overall bilingual advantage. Furthermore, 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 socioeconomic status (indicated by 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 late bilingual group, 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 or 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 already be 'proficient' in the L2, therefore this may 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.

Another study, Kapa and Columbo (2013) investigated the attentional control of monolingual children, Spanish-English bilingual children who had learned both languages before the age of 3, and Spanish-English children who had learned English after age 3. Attentional control is a cognitive skill in which one can ignore unnecessary or impertinent information to the task at hand. Children were tested using an Attention Network Test. Although all groups obtained the same accuracy rates, the researchers found that early L2 learners (those who learned both languages before the age of 3) had the fastest reaction time. The late learners and monolinguals did not significantly differ on response time, illustrating that early L2 acquisition could be a decisive factor in executive control levels.