Двуязычие: когнитивные преимущества и исторические перспективы.

Bilingualism, a subset of multilingualism, means having proficiency in two or more languages. A bilingual individual is traditionally defined as someone who understands and produces two or more languages on a regular basis. A bilingual individual's initial exposure to both languages may start in early childhood, e. g. before age 3, but exposure may also begin later in life, in monolingual or bilingual education. Equal proficiency in a bilingual individuals' languages is rarely seen as it typically varies by domain. For example, a bilingual individual may have greater proficiency for work related terms in one language, and family related terms in another language. Research on how a bilingual individual's first language (L1) and second language (L2) interact shows that both languages have an influence on the function of one another and on cognitive function outside of language. Research on executive functions like working memory, perception, and attentional and inhibitory control, suggests that bilinguals can benefit from significant cognitive advantages over monolingual peers in various settings. it is now believed that being bilingual adds to an individual's abilities rather than subtracting from it. There is, however, strong disagreement over how findings on this subject should be interpreted. Systematic reviews and meta analyses of executive functioning studies have failed to find compelling evidence for cognitive advantages in healthy adults or in participants across a broader age range. Moreover, the distribution of effect sizes in meta analyses suggest publication bias, or that the reporting of bilingualism effects on executive functioning give a distorted view of the evidence. They also thought that children learning two languages at a young age would struggle differentiating and building proficiency in two languages to become competent in either. According to a historical review in "The Journal of Genetic Psychology," various researchers held these beliefs, noting a "problem of bilingualism" or the "handicapping influence of bilingualism." Following studies reported that bilinguals performed worse in IQ tests and suffered in most aspects of language development. Many of these studies also used unstandardized and subjective definitions of bilingualism and of a bilingual individual, labeling someone as bilingual or monolingual through assumptions based on parent national origin, or based on family name. Their ideas led others to consider the role of human development more. In 1962, a turning point came about from a study that emphasized the importance of controlling for factors like age, sex, and SES, as well as of having a standardized measure for bilingualism when selecting a sample of bilinguals to be studied. Researchers carefully matched bilingual to monolingual participants and found that the bilinguals appeared to have significant advantages to that of their monolingual peers, outperforming in both verbal and non verbal tests, more specifically in the non verbal tests. In continuation of this study, research after this point began to shift focus, investigating areas of cognitive development and aptitude like perception and executive functioning. In 1967, publication of Lenneberg's seminal book, Biological Foundations of Language, first introduced the idea of a critical period of language acquisition, now better known as a sensitive period and further influenced bilingualism ideas. This study played a large role in our understanding of multilingualism and the effects that it has on the brain. Since the late 1970s, researchers have found more cognitive benefits of bilingualism, including better attention, task switching, and protection against aging declines. Over time, the prevalence of bilinguals in the United States has also increased. While the United States Census Bureau does not directly poll for bilingualism, they do poll for household languages. Non English speaking households are also surveyed for English proficiency. A 2012 interpretation of Census Bureau results observed that 11% of the population was bilingual in 1980, 14% in 1990, and 20% in 2012.

Executive function is the group of high level cognitive processes that assists in goal oriented tasks, such as problem solving, mental flexibility, attentional control, inhibitory control, and task switching. Much of the current research on cognitive effects of bilingualism studies the potential relationship between bilingualism and executive function; monolinguals and bilinguals may have executive function differences. Studies that match age and background factors like SES have found that bilinguals, who experience the mental demands of learning multiple languages, may have greater executive control and experience other cognitive benefits than their monolingual peers. Executive function may also have effects for older adults. Adults who learned a second language at a young age show better control and inhibitory processing than monolingual adults, as well as greater protection from cognitive decline such as dementia. Notably, some scientists continue to debate whether a bilingual advantage in executive functioning exists, with some studies and meta analyses coming to opposite conclusions.

Unimodal bilinguals are individuals who are proficient in two spoken languages. In contrast, bimodal bilinguals are individuals who are proficient in languages in differing modalities (i. e. a spoken and signed language). Studies have indicated that unimodal and bimodal bilinguals face different factors and requirements for their language use. In a monolingual conversational situation, unimodal bilinguals must suppress their use of one of their languages more significantly than bimodal bilinguals, while using the other language. This is because the use of a spoken word in another language would be confusing to the listener, whereas the use of a signed word would be less distracting to a listener, even when they do not know the meaning of the sign. In 1998, David Green proposed his "inhibitory control model", which 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 comparing unimodal bilinguals and bimodal bilinguals. Because bimodal bilinguals can express themselves in both languages at the same time, they may require less inhibition. This idea was supported by the results of the study; only unimodal bilinguals were found to have an advantage, as measured by the flanker task (a cognitive task that measures attentional focus and inhibition). Bimodal bilinguals also switch languages less frequently, because they are more likely to use both languages at once than to completely switch from one to the other. For this reason, the researchers of this study hypothesized that it may be the switching between languages that gives unimodal bilinguals the advantage.

Hakuta and Diaz Mixed experimental results have led to bitter, opposing views. and non uniform definitions. Furthermore, they argue that bilinguals are not consistently better at all executive function tasks Conversely, researchers in support of a bilingualism advantage note that while tests of executive function may undermine the robustness of findings, opposing findings come from researchers outside of the bilingualism field, and new neuroimaging technologies robustly verify and build upon historical findings of a bilingualism advantage.

Bilinguals often have more knowledge in certain language domains, leading to a dominant "L1" language, and a less dominant "L2" language. Research shows that when a bilingual individual proficient in both uses only L1 or L2, both languages are simultaneously active, phonologically and semantically, and share overlapping neural representations This activation is shown by electrophysiological measures of performance when listening to speech, reading words in either language or even planning speech in either language. Bilingualism studies historically looked at languages that share the Roman alphabet, where co activation of languages may make more intuitive sense. However, co activation of L1 and L2 has also been reported in bilinguals whose two languages have different scripts (writing systems), lexical forms (e. g. Japanese and English), and modality (e. g. English and American Sign Language). The fact that both languages are constantly activated means that they potentially compete for cognitive resources; bilinguals need a way to control the competition, 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. Inhibition may be the executive control system that allows successful linguistic selection even when both languages are co activated in bilinguals. De Groot & Christofells (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. Inhibiting language in different ways may impact non linguistic and linguistic cognitive processing. For example, a test that is widely used to assess this executive function is the Stroop task, where the word for a color is printed in a different color 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 color. Bilinguals compared to monolinguals have shown better Stroop task performance, suggesting that bilinguals have a more developed inhibition process, potentially due to the constant inhibition of their non target language.

Bilingual individuals have also shown advantages in metalinguistic ability, which 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. Metalinguistic awareness involves inhibition, or the ability to suppress distracting information such as semantics. Metalinguistic 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. Improved theory of mind, which is the ability to understand someone else's thinking, has also been implicated in bilingualism. A meta analysis in 2018 found that bilingual children performed better on a theory of mind test compared to monolingual children.

There has been a growing research 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 protect against age related cognitive deficits. Elderly bilinguals show better task switching skill, can ignore unrelated information, and can choose the best phrasing. Cognitive reserve is the idea that engaging in stimulating physical or mental activity can maintain cognitive functioning in healthy aging and delay the onset of dementia related memory losses. To test the protection of bilingualism against Alzheimer's disease (AD), Bialystok et al. (2007) Note 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, delaying symptom onset for those with the disease. For example, in one Alzheimer study, 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. Several other studies used the flanker test to study unimodal bilinguals and monolinguals matched based on education level and SES. While this study had a relatively small sample size, the results did confirm previous research findings: the bilinguals outperformed the monolinguals on all experimental tasks, and the monolinguals' neural imaging showed more signs of age related effects on performance of tasks and less gray matter density, which is associated with memory and function losses. Conversely, the bilinguals' neural imaging showed more gray matter density. Native bilingual children who develop proficiency in L1 and L2 at the same time, perform better on executive function tasks such as the Attention Network Test, which measures attentional control, compared to their late bilingual and monolingual counterparts in studies controlled for age, verbal ability, and SES. In his studies, he observed that Hildegard had "loose connections" between the (phonetic) structure of words and their semantics (meaning) because of her frequent substitutions of English words with German words and vice versa. This was noted in her everyday speech and well rehearsed songs or rhymes. He noted that she had a greater flexibility in the use of language that was unobserved in monolingual children of her age. Leopold considered that perhaps this loose connection between the meaning and form of a word could result in more abstract thinking or greater mental flexibility for bilingual children. Following this study, several others were formed to test similar things and find out more about the mental abilities of bilinguals with relation to their languages.

Anita Ianco Worrall, author of Bilingualism and Cognitive Development, designed a study to test Leopold's These areas are quite difficult for a child to learn, but with development through childhood, have been shown to increase the understanding the structure of language and introduce a greater awareness of meaning. Bilinguals develop what is referred to as metalinguistic awareness. Comparisons to monolinguals suggested a literacy advantage, as the bilingual children achieved scores equal to monolinguals one year older. This may be attributed to greater connections between spoken and written languages. Other bilingual researchers found a relationship between phonological awareness and word recognition in native Spanish speaking children learning to read English; phonological and word skills predicted how well a child could recognize English words. This suggested bilinguals could apply phonological awareness developed in L1 to the reading ability in L2.

Past research suggests that bilinguals have a smaller vocabulary size than their monolinguals counterparts. 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, such as the Peabody Picture Vocabulary Test and Boston Naming task. A possible explanation may be that the frequency of use of words is related to increased lexical accessibility, meaning that words that are used more frequently are accessed more quickly.

It has been suggested that prolonged naturalistic exposure to L2 affects how L2 is processed, but it may also affect how the L1 is processed. For example, in immersion contexts, the individual experiences reduced access to L1 and extensive contact with L2, which affects and facilitates processing of L2. However, this may also consequently affect processing of their L1, such as with increased difficulty in naming objects and phonology. To test this hypothesis, Dussias & Sagarra (2007) investigated how individuals interpreted temporarily ambiguous phrases. For example, 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 el hijo = the son as they have a high attachment preference, meaning they attach the modifier to the "higher" verb phrase [shot the son]. This differs from monolingual English speakers who will typically answer the actress as they have a low attachment preference, meaning they attach the modifier to the "lower" verb phrase [the actress who was on the balcony]. The researchers found that Spanish English bilinguals in a Spanish speaking environment showed preference for the typical Spanish high attachment strategy. However, 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, making it more available to them. But altogether, this supports the idea that the L2, English in this case, is affecting the way the native Spanish speakers use their L1.