Psychology Article Summary

Psychology Article Summary

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Current Directions in Psychological
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DOI: 10.1177/0963721409358571
Current Directions in Psychological Science 2010 19: 19
Ellen Bialystok and Fergus I. M. Craik
Cognitive and Linguistic Processing in the Bilingual Mind
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Cognitive and Linguistic Processing in the
Bilingual Mind
Ellen Bialystok1 and Fergus I. M. Craik2
1 York University and 2 Rotman Research Institute of Baycrest
Abstract
The article reports research investigating the way bilingualism affects cognitive and linguistic performance across the life span. In
general, bilingualism appears to have both benefits and costs. Regarding costs, bilinguals typically have lower formal language
proficiency than monolinguals do; for example, they have smaller vocabularies and weaker access to lexical items. The
benefits, however, are that bilinguals exhibit enhanced executive control in nonverbal tasks requiring conflict resolution, such
as the Stroop and Simon tasks. These patterns and their consequences are illustrated and discussed. We also propose some
suggestions regarding underlying mechanisms for these effects.
Keywords
executive function, language proficiency, development, aging
It is an obvious fact that human cognitive processes are heavily
dependent on linguistic abilities, but does the number of languages one speaks also shape the mind? For many years,
responses to this question emphasized the negative consequences of bilingualism, even warning that speaking two languages created retardation in children! So it was surprising
when a radically different answer was offered by Peal and
Lambert (1962); they showed that bilingual francophone children in Montreal outperformed monolingual Englishspeaking children on a wide variety of measures. The modern
era of bilingual research was born.
The great bulk of research since that time has compared linguistic processing in the bilingual individual’s two languages.
But the question we address here is different: How does bilingualism affect cognitive and linguistic processes in general?
Increasingly, evidence has pointed to broadly based effects of
experience on cognitive and brain organization, such as the
enlarged hippocampus in London taxi drivers (Maguire et al.,
2000). Is bilingualism an experience with the potential to alter
the mind and brain?
Studies seeking evidence for bilingual effects on development began with the conservative assumption that any detectable effect of a linguistic experience would be found in the
domain of linguistic competence. Thus, during the 1970s and
1980s, investigators explored the development of metalinguistic awareness in monolingual and bilingual children. Metalinguistic awareness is the explicit knowledge of linguistic
structure and the ability to access it intentionally, abilities that
are crucial to children’s development of complex uses of language and the acquisition of literacy.
The early research on metalinguistic development in monolingual and bilingual children revealed an important divide. In
several studies (e.g., Bialystok, 1988; Cromdal, 1999), monolingual and bilingual children were equally capable of detecting grammatical violations in meaningful sentences (e.g.,
‘‘Apples growed on trees’’), a typical measure of metalinguistic
functioning in children. When the sentences were semantically
anomalous, however (e.g., ‘‘Apples grow on noses’’), successful performance requires the ability to ignore the misleading
meaning and focus only on the grammar. Bilingual children
were more accurate in these cases. Thus, counterintuitively,
their additional linguistic experience did not benefit linguistic
knowledge but rather some process associated with access to
that knowledge. Put this way, the bilingual advantage in judging sentences has less to do with metalinguistic knowledge
than with an attentional advantage in selectivity and inhibition.
These processes are signature components of executive
functioning.
Corresponding Author:
Ellen Bialystok, Department of Psychology, York University, 4700 Keele Street,
Toronto, Ontario M3J 1P3, Canada
E-mail: ellenb@yorku.ca
Current Directions in Psychological
Science
19(1) 19-23
ª The Author(s) 2010
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DOI: 10.1177/0963721409358571
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Bilingualism and the Executive Function
System
The development of the executive-function system, located in
the prefrontal cortex, is the most crucial cognitive achievement
in early childhood. Children gradually master the ability to control attention, inhibit distraction, monitor sets of stimuli,
expand working memory, and shift between tasks. Importantly,
these are the same cognitive processes that show the first evidence of decline in aging. Therefore, if bilingualism affects
executive functioning, the impact should be found across the
entire cognitive system and throughout the entire life span.
Accumulating evidence supports the claim for a lifelong
positive effect of bilingualism on these executive-control processes. Typically, the research compares performance by
monolinguals and bilinguals on tasks that are superficially similar but includes one condition that additionally requires some
aspect of executive control. For example, Bialystok and colleagues (Bialystok, 1999; Bialystok & Martin, 2004) gave the
dimensional-change card-sort task (DCCS; Zelazo, Frye, &
Rapus, 1996) to 4- and 5-year-old children. In this task, children sort cards either by the color (red, blue) or shape (circle,
square) of diagrams on the cards. Participants first sort by one
dimension (e.g., color) but are later instructed to switch to the
other dimension (e.g., shape). Young children typically persist
in sorting by the original dimension. However, bilinguals were
more successful in switching to the second dimension following the rule change, indicating higher levels of executive control. Figure 1 presents the scores on the critical post-switch
condition in two studies.
In another study, 6-year-old children were comparable in
locating a hidden shape in a complex drawing in the Children’s
Embedded Figures Task, but bilinguals were more able to
change their interpretation of an ambiguous figure (e.g., the
duck-rabbit) to acknowledge the other image (Bialystok &
Shapero, 2005). Both tasks require perceptual analysis, but
only the ambiguous-figures task requires inhibiting the original
meaning of the stimulus. Carlson and Meltzoff (2008) refined
this position by demonstrating an advantage for 6-year-old
bilingual children in executive-control tasks that require inhibition of attention to conflicting response options but not in tasks
requiring inhibition of a habitual response to a familiar stimulus. Kova´cs and Mehler (2009) recently extended this pattern to
infants. They found that 7-month-old infants raised in bilingual
households were better able to switch responses after a rule
shift (cf., DCCS) than were their peers raised in monolingual
households.
Research with adults has revealed parallel results, showing
for example faster bilingual responding to conflict conditions
in the Stroop task (Bialystok, Craik, & Luk, 2008a) and flanker
task (Costa, Herna´ndez, & Sebastia´n-Galle´s, 2008). Bilinguals
were less disrupted than monolinguals when the response to a
stimulus required participants to ignore a competing but irrelevant feature of the stimulus. This enhanced bilingual performance persists into older age, sometimes showing a slower
rate of decline than that found in healthy older monolinguals.
One illustrative experiment by Bialystok and colleagues
(Bialystock, Craik, Klein, & Viswanathan, 2004) involved several reaction-time (RT) conditions. In the simplest condition,
one of two color patches was presented in the center of a computer screen and the task was to press the relevant response key
as rapidly as possible. In another condition, the colored patch
appeared at the side of the screen, either above the relevant key
(congruent) or on the opposite (incongruent) side. The longer
time needed to respond in the incongruent presentation compared to the congruent one is called the Simon effect; larger
Simon effects imply greater difficulty in suppressing the irrelevant spatial information. Figure 2a shows results for the first
condition (simple RT) as a function of age and language group,
and Figure 2b shows the Simon Effect for the same groups.
Older participants respond more slowly, but there are no differences between monolinguals and bilinguals on the simple condition (Fig. 2a). However, the size of the Simon effect in Figure
2b indicates a larger disruption for monolinguals than bilinguals that appears to increase in the older groups. This result
suggests that bilingualism may protect against age-related cognitive decline—at least in the ability to inhibit the disruptive
effects of misleading stimuli.
Linguistic Ability and Executive Control
The bilingual story is not all positive, however. Studies of
vocabulary knowledge have consistently reported lower scores
for bilinguals in each language than for monolingual speakers
of that language, and this deficit appears at all ages across the
life span (Bialystok, 2001). In a study examining receptive
vocabulary scores in English for more than 1,700 children
between the ages of 3 and 10 years old, monolingual children
obtained higher scores than bilingual children at every age,
even though all the bilingual children were fluent in English
and used it daily at school (Bialystok, Luk, Peets, & Yang, in
0
2
4
6
8
10
Study
Mean no. correct
Monolingual Bilingual
B 1999 B&M 2004
Fig. 1. Mean number correct (out of 10) and standard error by
language group (monolingual or bilingual) in the post-switch
condition of the dimension-change card-sort task in two studies.
B 1999 ¼ Bialystok (1999); B&M 2004 ¼ Bialystok & Martin
(2004).
20 Bialystok, Craik
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press). Similarly, studies of language processing in adults have
documented disadvantages for bilinguals in tasks that require
rapid lexical access and retrieval. Bilinguals are slower and commit more errors in picture naming even in their dominant language, obtain lower scores on verbal-fluency tasks, experience
more tip-of-the-tongue states, and demonstrate more interference in lexical decision (Michael & Gollan, 2005). Although
these deficits are not apparent in conversational interactions with
bilinguals, their persistence in controlled experiments signals a
pervasive negative impact of two language systems on linguistic
performance. This pattern of positive and negative effects
prompts two related questions: First, do the two conflicting
influences co-exist in the same individuals? And second, if they
do, are the effects independent or interactive?
The first question was addressed in a study of younger and
older adults by Bialystok et al. (2008a). In this study, four
groups of participants who were younger (20–30 years) or older
(60–80 years) monolinguals or bilinguals completed tasks that
assessed either language proficiency and lexical access or nonverbal executive functioning. The main findings were that
monolinguals performed better on the former set of tasks,
whereas bilinguals performed better on the latter. Younger participants showed higher levels of performance on most tasks,
although the older adults were better on tasks tapping vocabulary knowledge. Additionally, there was some evidence for
larger language–group differences in older participants on
executive control tasks, suggesting that bilingualism may compensate to some extent for the typical age-related decline of
executive functions. These results appear to show that lexical
and executive processes are independent, but on other tasks
these demands are often combined—language processing frequently requires executive control. How do monolinguals and
bilinguals perform in such situations?
We have investigated these interactions through several paradigms. One example is the release from proactive interference
(PI) task, in which participants are asked to recall items from
successively presented lists of words that belong to the same
semantic category. With each new list, interference builds up
from previous lists and performance declines as participants
become less able to encode new specifics and to discriminate the
current list at retrieval. After three such lists, the fourth list presents words from a different semantic category and recall performance is restored. Executive control is involved in the ability to
focus on the current list at encoding and retrieval. In two studies,
PI was shown to be less problematic for both 7-year-old children
and young adults who were bilingual than for their monolingual
counterparts, in spite of lower proficiency on a vocabulary test in
both cases (Bialystok & Feng, 2009).
A clear dissociation between levels of language proficiency
and executive control over accessing that language is possible
through the two subtests of the verbal-fluency test. This is a
neuropsychological assessment instrument used to diagnose
difficulties in brain function. In the semantic-fluency condition, participants are given 60 seconds to generate words that
belong to a particular category, such as animals. Because the
instruction is compatible with the organizational principle of
linguistic representation—that is, there are closer associative
links among names for animals than between the name for an
animal and the name for a flower—the number of responses
provides an index of vocabulary size or language proficiency.
In the letter-fluency condition, participants are asked to generate words that begin with a particular letter and to observe a set
of restrictions: No proper names, no numbers, and no variations
on the same word. Given the combination of the requirement
for an effortful search through representational space and the
restrictions that require monitoring and working memory, the
letter-fluency task assesses both language proficiency and
executive control. Typically, bilinguals have smaller vocabularies than monolinguals do, and the usual finding is that bilinguals generate fewer words on the semantic-fluency task than
do monolinguals but that they sometimes perform as well as
monolinguals on the letter-fluency task. A study by Bialystok,
Craik, and Luk (2008b) selected bilinguals who either performed more poorly than monolinguals on a vocabulary test
or were matched in performance to monolinguals for vocabulary, with all other cognitive measures equivalent for the three
0
150
300
450
600
750
900
1050
1350
1200
1500
(a) (b)
30-39 40-49 50-59 60-69 70-79
Mean RT (ms)
Age
Monolingual Bilingual Monolingual Bilingual
0
100
200
300
400
500
600
700
800
900
1000
30-39 40-49 50-59 60-69 70-79
RT Difference (ms)
Age
Fig. 2. Mean reaction time (RT) by decade for monolinguals and bilinguals. (a) Mean RT for control condition. (b) Mean RT cost as the
difference between congruent and incongruent trials (Simon effect). From Bialystok, Craik, Klein, & Viswanathan (2004).
Bilingual Mind 21
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groups. Consistent with previous research, the unmatched
bilinguals generated fewer words in the category task than did
monolinguals or vocabulary-matched bilinguals. However, the
vocabulary-matched bilinguals generated more words than did
monolinguals or unmatched bilinguals on letter fluency, showing the advantage of executive control once proficiency deficits
were eliminated. These results are shown in Figure 3.
Mechanism for the Bilingual Advantage
It is well established that the representational systems for both
languages of a well-practiced bilingual are active and potentially available when that individual is speaking in either language. Our suggestion is that the mechanism recruited to
resolve the potential conflict from the two language systems
and select appropriately from the target language is some
domain-general aspect of executive control. The necessity
to use this conflict management system continuously
enhances its function, with consequent benefits to control in
both language and nonlanguage tasks. One test of this hypothesis is to compare bilinguals for whom conflict is always present with those for whom conflict is less intrusive—for
example, speech–sign bilinguals who can resolve the conflict
by simply producing both languages simultaneously. In a
study comparing monolinguals, bilinguals, and speech–sign
bilinguals, advantages in executive control on a nonverbal
flanker task were found only for the verbal bilinguals
(Emmorey, Luk, Pyers, & Bialystok, 2008).
Does Bilingualism Protect Against Cognitive
Decline?
In all the studies described here, participants were selected to
be healthy and free from cognitive impairment. But aging
sometimes includes challenges such as dementia. Given the
sustained advantage of bilinguals into older age, does bilingualism continue to offer protection in such cases? A large body
of research has pointed to the importance of ‘‘cognitive
reserve,’’ the protection against cognitive decline that comes
from active engagement in stimulating intellectual, social, and
physical activities (Stern, 2002). To examine whether bilingualism contributes to cognitive reserve, we compared the age of
onset of symptoms in 91 monolingual and 93 bilingual patients
who had been diagnosed with dementia. With all else being
equal, the age of dementia onset for the bilinguals was 4 years
later than it was for the monolinguals—a highly significant difference (Bialystok, Craik, & Freedman, 2007). A four-year
delay of symptoms of dementia is much greater than any effect
associated with drugs and represents considerable savings in
health care costs.
Conclusions
This body of research has converged on the conclusion that the
experience of speaking two languages on a regular basis has
broad implications for cognitive ability, enhancing executivecontrol functions across the life span. Ironically, the only
recorded negative consequences of bilingualism are on verbal
knowledge and skill—specifically, smaller vocabularies and less
rapid access to lexical items. But this is easily outweighed by the
evidence supporting a range of advantages in the development,
efficiency, and maintenance of executive functions. The finding
that bilingualism defers the onset of dementia by 4 years, if
confirmed by further studies, is a particularly dramatic benefit.
The evidence at present thus shows that speaking more than one
language does indeed appear to have a beneficial effect on
aspects of cognitive control. This conclusion raises a number
of questions. What about three languages? Is the trilingual
5
10
15
20
25
30
Category Letter
Verbal-Fluency Condition
Mean Number Words
Monolinguals Bilinguals Low Vocabulary Bilinguals Matched Vocabulary
Fig. 3. Number of words generated on category-fluency and letter-fluency subtests of the verbalfluency task for monolinguals, bilinguals with lower vocabulary, and bilinguals with vocabulary matched
to monolinguals. From Bialystok, Craik, and Luk (2008b).
22 Bialystok, Craik
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advantage even greater? And does the relation between two languages make a difference? That is, does speaking two related
languages, such as Spanish and Italian, give a greater (or lesser)
advantage than speaking unrelated languages such as English
and Chinese? Perhaps most intriguingly, what is the neural basis
of the bilingual advantage? Are these performance differences
mirrored in functional architecture or structural properties of the
brain? Many questions remain for future studies.
Recommended Reading
Bialystok, E. (2001). (See References). A monograph providing an
overview of the cognitive implications of bilingualism for children’s development.
Craik, F.I.M., & Bialystok, E. (2006). Cognition through the lifespan:
Mechanisms of change. Trends in Cognitive Sciences, 10, 131–
138. A brief statement describing the roles of representation and
control in life span development, incorporating the influence of
experiences such as bilingualism.
Diamond, A. (2002). Normal development of prefrontal cortex from
birth to young adulthood: Cognitive functions, anatomy, and biochemistry. In D.T. Stuss & R.T. Knight (Eds.), Principles of frontal
lobe function (pp. 466–503). Cambridge, MA: MIT Press. A chapter providing a thorough description of the development of executive functions throughout childhood.
Michael, E.B., & Gollan, T.H. (2005). (See References). A good
review of the literature showing deficits for bilinguals in performance on verbal tasks.
Declaration of Conflicting Interests
The authors declared that they had no conflicts of interest with respect
to their authorship or the publication of this article.
Funding
This work was partially supported by Grant R01HD052523 from the
U.S. National Institutes of Health to EB, Grant A2559 from the Natural Sciences and Engineering Research Council of Canada to EB, and
by Grant MOP57842 from the Canadian Institutes for Health Research
to both authors.
References
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Bilingual Mind 23
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