One of the most crucial cognitive developments in early childhood is the emergence of the executive function system (Diamond, 2002
). These executive processes are the basis for all higher thought, including control of attention (needed for selection and inhibition of the variety of environmental cues), working memory (needed for planning and maintaining set), and switching (needed for multitasking). Research with preschool children has shown that bilingual children develop control over these executive processes earlier than monolingual children (Bialystok, 2001
). Importantly, these bilingual advantages are found not only on verbal tasks where executive control to resolve conflict between form and meaning gives bilinguals an advantage on metalinguistic tasks (Bialystok, 1988
; Cromdal, 1999
; Galambos & Goldin-Meadow, 1990
) but also on nonverbal tasks where no explicit linguistic processing is involved (reviewed below).
The basis for the bilingual advantage is commonly assumed to be in the constant need for bilinguals to control attention to two language systems, a process that boosts those attentional processes for all tasks including nonverbal ones. But how much experience in attending to two languages is necessary for these generalized effects to appear? If these advantages to the executive control system build up as a function of their use in language management, then it may be that very young bilinguals do not show the same degree of cognitive effect because their experience with bilingual language use is more limited. In this case, few differences between monolinguals and bilinguals would be found in very young children, but greater differences would be expected at around 4 years old, the age investigated in much of the previous literature.
In contrast to this prediction, studies have shown diverging developmental patterns in speech perception and word learning for infants raised in bilingual homes even in the first year of life. In terms of speech perception, Catalan-Spanish bilingual infants showed a delayed reorganization for vowels, occurring around 12 months of age, which is about four months later than in their monolingual peers (Bosch & Sebastian-Galles, 2003
). Additionally, bilingual infants appear to differ from monolingual infants in the way they acquire a lexicon. Fennell, Byers-Heinlein, and Werker (2007)
showed that bilingual infants postpone the use of phonetic details to guide their word acquisition until 20 months of age, whereas their monolingual peers succeed in this task three months earlier. More dramatically, Kovacs and Mehler (2009)
reported differences between monolingual and bilingual 7-month-olds in their ability to switch their attention to a novel cue for a visual reward. These findings suggest that cognitive and linguistic networks are organized differently for monolingual and bilingual children from the first year of life.
There are three purposes for the present study. The first is to examine the possibility that there is a bilingual advantage for executive control in preschool children who are younger than those studied in previous research. The second is to determine whether potential differences in executive control are associated with different word mapping strategies for young monolingual and bilingual children. The third is to examine the generality of such effects by including two groups of monolinguals from different cultures and languages as the point of comparison for the bilingual children. The results will help to understand the origin of cognitive and language differences that can be attributed to bilingualism by identifying potential effects early and examining the generality of these effects across different groups. Such information would constrain interpretations of the mechanism responsible for the reported cognitive consequences of bilingualism.
A growing number of studies converges on the conclusion that bilingualism affects children’s development of executive control. Bilingual children are more successful than monolinguals on the dimensional change card sort task (Bialystok, 1999
; Bialystok & Martin, 2004
) developed by Zelazo, Frye, and Rapus (1996)
, a written version (Pascual-Leone, 1969
) of Piaget and Inhelder’s (1956)
water-level task (Bialystok & Majumder, 1998
), the attentional networks test (ANT: Mezzacappa, 2004
; Yang, Shih, & Lust, 2005
) developed by Rueda, Fan, McCandliss, Halparin, Gruber, Lercari, & Posner (2004)
, and theory of mind tasks (Bialystok & Senman, 2004
; Goetz, 2003
; Kovacs, 2009
). The children in these studies ranged between about 4 and 8 years of age. The common feature is that responses are based on conflict between competing options. For example, in the Simon task used by Martin-Rhee and Bialystok (2008)
with 5-year-old children, a stimulus associated with a left or right key press is presented on the left or right side of the display, creating congruent and incongruent trials determined by the relation between the presentation and response sides. Bilinguals performed this task more rapidly than monolinguals, showing faster response times for both congruent and incongruent trials if they were presented in a mixed block. Conditions in which the stimuli were presented in the center of the screen so there was no conflict were performed similarly by monolinguals and bilinguals.
This research demonstrates more efficient performance by bilinguals, but the mechanism underlying that advantage is not clear. Early speculation pointed to advanced inhibitory control as the mechanism (e.g., Bialystok, 2001
), but that explanation may be too narrow. For example, inhibitory control would not explain why bilinguals perform congruent trials more rapidly than monolinguals in studies that include both congruent and incongruent trials (Bialystok, in press
; Bialystok, Craik, Klein, & Viswanathan, 2004
; Bialystok, Craik, & Ryan, 2006
; Costa, Hernandez, & Sebastian-Galles, 2008
; Martin-Rhee & Bialystok, 2008
). Another executive function component, such as cognitive flexibility, must also be involved to explain how bilinguals monitor the context and switch between changing trials and rules in order to perform more efficiently than monolinguals in congruent trials as well as incongruent ones. At the same time, inhibitory control is too broad an explanation. In a study by Carlson and Meltzoff (2008)
, a battery of tasks requiring various types of inhibition was presented to monolingual and bilingual children; bilingual children performed better than monolinguals on tasks that required resolving conflict between competing responses but not on tasks that required withholding a primed response, even though that too is an aspect of inhibitory control. Moreover, aspects of executive control that have little role for inhibition, such as working memory, also demonstrate some bilingual advantage (Feng, Diamond, & Bialystok, 2007
). Evidence from an earlier stage in development will help us to understand these issues.
Monolingual and bilingual children also differ in aspects of lexical development. In general, both the course and rate of language development for monolingual and bilingual children are similar (Lindholm, 1980
; de Houwer, 1995
), but the vocabulary controlled by a bilingual child in each
language is smaller than that of a comparable monolingual (Bialystok et al., in press
; Oller & Eilers, 2002
). This outcome may simply reflect the fact that their language-learning experience is divided between two languages, but it may also be that the process
of vocabulary learning is different for bilingual children. Minimally, bilingual children have an additional referential system that could be incorporated into their word-learning experiences. Therefore, our question is whether monolingual and bilingual children use different attentional resources for mapping new words to meanings.
One influential account of word learning in young children is the mutual exclusivity (ME) hypothesis (Markman & Wachtel, 1988
; Markman, 1989
). Although its developmental origins and interpretation are controversial, the assumption is that ME is a natural constraint that restricts preschoolers’ assumptions about word meanings and word extensions. Children believe that labels for objects are mutually exclusive, that is, a given object can only have one name (Markman, 1989
; Woodward, 2000
for discussion). Moreover, the tendency for this assumption to influence children’s naming behavior increases during the preschool years (Au & Glusman, 1990
; Merriman & Bowman, 1989
), and some have suggested that it is a heuristic that children learn to use as they get older (MacWhinney, 1991
). Others have proposed that the constraint may be a default strategy that children use when other options are not available (Merriman & Bowman, 1989
; Markman, 1992
The ME strategy incorporates an element of attention and includes a small but perceptible degree of conflict: a novel word in the context of a familiar and unfamiliar object can potentially refer to either item. The ME hypothesis is one resolution for that conflict because it assigns the new word to the unfamiliar object in order to satisfy the need for each object to have one name. Because it is based in conflict, it is possible that bilingual children will resolve the relation between a novel word and two potential object referents differently from monolinguals. Specifically, bilingual children should be less constrained by ME than monolinguals because the conflict between the novel word and the two objects is less salient. There are three possible reasons for this outcome: first, the enhanced conflict resolution processes of bilingual children will simply assign the new word to one of the objects without effort; second, the experience of knowing multiple labels for the same object will diminish the conflict at the outset because it is known that things can have two names; and third, the greater cognitive flexibility of bilingual children will allow them to override the ME bias and accept two verbal representations for a given object. In all three cases, the prediction is that there should be less evidence of ME in bilingual children.
Some research has investigated this issue but the results are contradictory. Some studies report less reliance of bilingual children on ME than matched monolinguals (Davidson, Jergovic, Imami, & Theodos, 1997
; Davidson & Tell, 2005
; Yow & Markman, 2007
) and others find no difference (Au & Glusman, 1990
; Frank & Poulin-Dubois, 2002
; Merriman & Kutlesic, 1993
). Although bilingual children are familiar with having two names for a particular object, it appears that the ME constraint does not apply if the words come from different languages, even for monolingual children (Au & Glusman, 1990
). Thus, there may be no difference between monolingual and bilingual children in adopting this strategy for words in the same language. However, inhibiting a given name and switching to a new one also requires cognitive flexibility, and this aspect of executive control is more developed in bilinguals. Thus, because of their advantage in executive control, bilingual children may be less bound by ME than monolinguals. No previous study has combined executive function tasks with mutual exclusivity to directly test the hypothesized relation between them.
Finally, comparisons of monolingual and bilingual children are always difficult because it is problematic to guarantee that the two groups are similar in all aspects except the relevant language experience. Ideally, it would be helpful to replicate the design in which monolingual and bilingual children are compared in two cultures, but there would still be differences between the cultures that made that design problematic. Instead, our approach is to incorporate an additional group of children from a different culture and compare them to one of the two language groups. In a previous study, Bialystok and Viswanathan (2009)
compared monolingual children in Canada with bilingual children in Canada and bilingual children in India on a set of executive function tasks. The results showed that the two bilingual groups performed similarly and both were different from the monolingual group, irrespective of country. The present study takes the opposite approach: children who are monolingual or bilingual in Canada are compared to an additional monolingual group from France. The hypothesis is that the two monolingual groups will perform similarly and that the bilingual group will be different from both, irrespective of country. Such results will confirm the generality of these effects and release them from the specific details of the culture or language that define the bilingual experience.
To summarize, the present study investigated whether the cognitive benefits of bilingualism can be detected in young preschool children, whether there are implications of bilingualism for children’s word-mapping strategies that may be related to differences in executive control, and whether the processing differences between monolinguals and bilinguals are sustained when the comparisons of language experience are made across cultural and linguistic contexts. To provide a broad test of the hypothesis of differences in executive control, a set of tasks was administered in which each task relied on a different component of control.