Several high-profile studies have shown that bilingual children outperform their monolingual peers in terms of several cognitive abilities – including tests of verbal and nonverbal problem-solving, selective attention, flexibility (e.g., task-switching) and others. These studies have captured the public imagination and probably guided many moms to expose their kids to a second language.
But a new article in Developmental Science suggests that these impressive results may be somewhat overblown: bilingual children may be likely to come from wealthier families than monolingual children (EDIT: this may not be true in general, but is plausibly true for the samples used to show a bilingual advantage, which predominantly come from Canada, where wealthier families may be more likely to speak both French and English). Since wealth has a strong and well-established relationship with cognitive function, these effects may be due not to a cognitive advantage but a financial one. None of the often-cited “bilingual advantage” papers seem to have measured socio-economic status independently.
To address this shortcoming, authors Morton & Harper asked 17 monolingual and 17 English-French bilingual 6-7 year-old children to complete a series of tasks to measure vocabulary (a picture naming test), selective attention (the Simon test, where subjects have to press one key for a red square and one key for a green square, but red squares may appear closer to the green key and vice versa, providing a measure of selective attention just to the color), and non-verbal intelligence (the Matrix Analogies test, which seems loosely similar to Raven’s Matrices). Every parent completed a questionairre on their socio-economic status (SES).
Not only did the results fail to show an effect of bilingualism on the Simon task (in contrast to some previous work by others) but they showed a strong effect of SES: children from higher-income families showed better selective attention on the Simon task (i.e., they were less slowed when the stimuli appeared near the incongruent response button).
Furthermore, this SES difference remained even after controlling for differences in nonverbal IQ, suggesting that the high SES advantage for selective attention is not merely due to differences in IQ between SES groups.
Although the current sample size was small, the significant SES results suggest that the sample size was not too small to detect group differences in general. Morton & Harper suggest that there are other reasons to suspect that bilingualism does not benefit cognitive function in the way many of the previous papers have described (in particular, those researchers had argued that bilinguals must constantly suppress or “inhibit” the language which they are not using at any particular time, leading to a benefit in the degree of control they can exert on their behavior).
Nonetheless, the study does raise another issue: why is there a relationship between SES and cognitive function, beyond differences in IQ? Important work by Martha Farah and colleagues has investigated this question in detail, and demonstrated that the differences seem less related to visual/spatial abilities as to the elusive “executive functions” and a fronto-temporal network of brain regions. The exact causes of these differences remain unknown, as do possible interventions. In the presence of these larger-scale differences driven by SES, the influence of multilingualism is likely to be small – a conjecture confirmed by Morton & Harper’s work described above.