Auditory processing and high task demands facilitate the bilingual executive control advantage in young adults

Abstract

Although bilingual children and elderly have been observed to outperform monolinguals in typical executive control tasks, this bilingual advantage is not consistently found in the young adult population. Proponents of the bilingual executive control advantage argue the reason for this is that task demands in the typical tasks used are not high enough, since young adults perform at ceiling level, whereas critics of the effect argue it has benefited from publication bias. Here we test the task-load hypothesis using a standard and a difficult version of the arrow-flanker task and identify stimulus processing characteristics underlying greater bilingual executive control. We increased task demands by using an “Opposite” task in which participants were to respond to the central arrow indicating its opposite direction whilst a task cue indicated which task was to be performed at each trial. Further increase in task difficulty was expected to arise from reducing the task preparation time by using different stimulus-onset-asynchronies between cue and target stimuli. As predicted, we observed no language group differences in the normal flanker task, whereas bilinguals displayed less errors than monolinguals and were less hampered by the difficult task than monolinguals when auditory task cues were used. Event-related potentials (ERPs) revealed that the bilinguals’ conflict monitoring response occurred much earlier than the monolinguals’ when the task cue was auditory but less so when the cue was visual. Indeed, bilinguals appeared to prioritize the cue signal when it was auditory, but not when it was visual. Further ERP results showed bilinguals displayed greater attentional responses to the target stimulus than monolinguals. Finally, the behavioral and conflict-monitoring ERP responses correlated with language proficiency and usage scores. Together, these results show that when tasks demands are high and auditory processing is part of the task, bilingual adults outperform monolinguals due to better stimulus identification and greater efficiency in managing task demands.