On the phantom-like appearance of bilingualism effects on neurocognition: (How) should we proceed?

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Abstract

Numerous studies have argued that bilingualism has effects on cognitive functions. Recently, in light of increasingly mixed empirical results, this claim has been challenged. One might ponder if there is enough evidence to justify a cessation to future research on the topic or, alternatively, how the field could proceed to better understand the phantom-like appearance of bilingual effects. Herein, we attempt to frame this appearance at the crossroads of several factors such as the heterogeneity of the term ‘bilingual’, sample size effects, task effects, and the complex dynamics between an early publication bias that favours positive results and the subsequent Proteus phenomenon. We conclude that any definitive claim on the topic is premature and that research must continue, albeit in a modified way. To this effect, we offer a path forward for future multi-lab work that should provide clearer answers to whether bilingualism has neurocognitive effects, and if so, under what conditions.

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Empirical assessment of published effect sizes and power in the recent cognitive neuroscience and psychology literature

Dénes Szücs, John P. A. Ioannidis (2017)

We have empirically assessed the distribution of published effect sizes and estimated power by analyzing 26,841 statistical records from 3,801 cognitive neuroscience and psychology papers published recently. The reported median effect size was D = 0.93 (interquartile range: 0.64–1.46) for nominally statistically significant results and D = 0.24 (0.11–0.42) for nonsignificant results. Median power to detect small, medium, and large effects was 0.12, 0.44, and 0.73, reflecting no improvement through the past half-century. This is so because sample sizes have remained small. Assuming similar true effect sizes in both disciplines, power was lower in cognitive neuroscience than in psychology. Journal impact factors negatively correlated with power. Assuming a realistic range of prior probabilities for null hypotheses, false report probability is likely to exceed 50% for the whole literature. In light of our findings, the recently reported low replication success in psychology is realistic, and worse performance may be expected for cognitive neuroscience.

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Bilingual advantages in executive functioning either do not exist or are restricted to very specific and undetermined circumstances.

Hunter A Johnson, Kenneth Paap, Oliver Sawi (2015)

The hypothesis that managing two languages enhances general executive functioning is examined. More than 80% of the tests for bilingual advantages conducted after 2011 yield null results and those resulting in significant bilingual advantages tend to have small sample sizes. Some published studies reporting significant bilingual advantages arguably produce no group differences if more appropriate tests of the critical interaction or more appropriate baselines are used. Some positive findings are likely to have been caused by failures to match on demographic factors and others have yielded significant differences only with a questionable use of the analysis-of-covariance to "control" for these factors. Although direct replications are under-utilized, when they are, the results of seminal studies cannot be reproduced. Furthermore, most studies testing for bilingual advantages use measures and tasks that do not have demonstrated convergent validity and any significant differences in performance may reflect task-specific mechanism and not domain-free executive functions (EF) abilities. Brain imaging studies have made only a modest contribution to evaluating the bilingual-advantage hypothesis, principally because the neural differences do not align with the behavioral differences and also because the neural measures are often ambiguous with respect to whether greater magnitudes should cause increases or decreases in performance. The cumulative effect of confirmation biases and common research practices has either created a belief in a phenomenon that does not exist or has inflated the frequency and effect size of a genuine phenomenon that is likely to emerge only infrequently and in restricted and undetermined circumstances.

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Are there bilingual advantages on nonlinguistic interference tasks? Implications for the plasticity of executive control processes.

Matthew Hilchey, Raymond M. Klein (2011)

It has been proposed that the unique need for early bilinguals to manage multiple languages while their executive control mechanisms are developing might result in long-term cognitive advantages on inhibitory control processes that generalize beyond the language domain. We review the empirical data from the literature on nonlinguistic interference tasks to assess the validity of this proposed bilingual inhibitory control advantage. Our review of these findings reveals that the bilingual advantage on conflict resolution, which by hypothesis is mediated by inhibitory control, is sporadic at best, and in some cases conspicuously absent. A robust finding from this review is that bilinguals typically outperform monolinguals on both compatible and incompatible trials, often by similar magnitudes. Together, these findings suggest that bilinguals do enjoy a more widespread cognitive advantage (a bilingual executive processing advantage) that is likely observable on a variety of cognitive assessment tools but that, somewhat ironically, is most often not apparent on traditional assays of nonlinguistic inhibitory control processes.