The interplay between bilingualism and sleep quality in modulating executive performance

We investigated the interactive effects of bilingualism and sleep on executive functioning at the behavioral level. We conducted two experiments using two independent samples of bilingual young adults, the Flanker task to assess executive performance, the Pittsburg Sleep Quality Index to measure retrospective sleep quality over a one-month period and the Insomnia Severity Index to assess insomnia-related symptoms. In Experiment 1, we registered bilingualism effects on executive performance in poor, but not in good sleepers. In Experiment 2, the magnitude of bilingual effects increased with increasing severity of insomnia symptoms. We conclude that when poor sleep quality and insomnia negatively affect cognitive resources, bilingualism-related cognitive effects emerge more prominently. This suggests higher degrees of bilingualism may compensate detrimental effects of poor sleep quality and insomnia on executive functioning. We suggest that cognitive research in bilingualism and sleep could benefit from controlling for interindividual variability in sleep quality and vice versa.