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The Effect of Second Language Proficiency on Inhibitory Control: An Ex-Gaussian Analysis

Eve Higby (Graduate Center of the City University of New York), Seamus Donnelly (Graduate Center of the City University of New York), & Jungmee Yoon (Graduate Center of the City University of New York)


Inhibition; Second language acquisition; Reaction time; Ex-Gaussian

Several studies have reported superior performance on executive function tasks for bilinguals compared to monolinguals (e.g., Bialystok et al., 2008). However, some researchers have reported issues replicating this effect (e.g., Paap & Greenberg, 2013). Two common methodological choices may account for the inconsistent findings. Most published research has treated bilingualism as a categorical variable and focused on RT means rather than other distributional parameters.

Most studies of executive functioning in bilinguals include those with high proficiency in both languages. However, bilinguals also include those with non-balanced proficiencies of various levels, meaning that degree of bilingualism is in fact a continuous variable. The strength of cross-language interference is likely modulated by the degree of bilingualism, suggesting that executive functions may improve as L2 proficiency develops. In this study, we tested the relationship between L2 proficiency and performance on an inhibitory control task.

Most published research on this topic has used RT means as the dependent measure. However, theoretical models of RT imply that distributional tails are often more sensitive to individual differences (Balota & Yap, 2011). One promising approach to studying individual differences in cognitive processing is examining ex-Gaussian parameters from RT distribution, which include separate parameters for central tendency and tails. Calabria et al. (2011) re-analyzed two existing data sets and found that bilinguals had smaller central tendencies (mu) and tails (tau) across both congruent and incongruent trials, but a bilingual advantage in the difference between congruent and incongruent trials was only observed in tau.

In this study, we tested 42 native speakers of Brazilian-Portuguese with varying degrees of English (L2) proficiency using a Flanker task. We predicted that L2 proficiency would correlate negatively with both mu and tau in overall RTs. Furthermore, we expected a three-way interaction between proficiency, parameter (mu, tau), and condition (congruent, incongruent) showing an effect of proficiency on tau, but not mu, for incongruent, but not congruent, trials.

Ex-Gaussian parameters were estimated and analyzed in a mixed-effects model with proficiency, parameter, condition, and their interactions as fixed effects. Results revealed a main effect of proficiency (B = -59.56, t(76.9) = -2.21, p = 03), and an interaction between proficiency and condition (B = -53.184, t(120) = -2.54, p = .01), indicating that higher-proficiency participants had smaller parameter estimates across both conditions and that this effect was larger in the incongruent condition. The interaction between proficiency and parameter was non-significant as was the three-way interaction between proficiency, parameter, and condition.

The results suggest that bilinguals have better performance across conditions with increasing proficiency, but the pattern is larger for the incongruent than congruent condition. These findings may indicate that bilinguals with higher L2 proficiency develop not only inhibitory control but also overall efficient processing abilities.



[1] Balota, D. A., & Yap, M. J. (2011). Moving Beyond the Mean in Studies of Mental Chronometry: The Power of Response Time Distributional Analyses. Current Directions in Psychological Science, 20(3), 160–166. doi:10.1177/0963721411408885

[2] Bialystok, E., Craik, F., & Luk, G. (2008). Cognitive control and lexical access in younger and older bilinguals. Journal of Experimental Psychology: Learning, Memory, and Cognition, 34(4), 859–873.

[3] Calabria, M., Hernández, M., Martin, C. D., & Costa, A. (2011). When the tail counts: the advantage of bilingualism through the ex-Gaussian distribution analysis. Frontiers in Psychology, 2, 1–8.

[4] Paap, K. R., & Greenberg, Z. I. (2013). There is no coherent evidence for a bilingual advantage in executive processing. Cognitive Psychology, 66(2), 232–258.