Bilingual speakers' enhanced monitoring can slow them down

Performance differences between bilinguals and monolinguals on conflict tasks can be affected by the balance of various sub-processes such as conflict monitoring and allocation of attentional resources for stimulus categorisation. Here we investigated the effect of bilingualism on these sub-processes during a conflict task with medium monitoring demand. We examined the behavioural responses and evoked potentials from bilinguals and monolinguals during a flanker task with 25% incongruent trials. We analysed behavioural differences by means of averaged response times and ex-Gaussian analyses of response time distributions. For the evoked potentials we focused on N2 (reflecting conflict monitoring) and P3 responses (reflecting allocation of attentional resources for cognitive control). We found that bilinguals had significantly longer response distribution tails compared to monolinguals. Additionally, bilinguals exhibited a more pronounced N2 and smaller P3 components compared to monolinguals, independent of experimental condition, suggesting a different balance of sub-processes for the two groups. It is suggested that bilinguals engaged more strongly in monitoring processes, leading to the allocation of fewer attentional resources during stimulus categorisation. Importantly, N2 amplitudes were positively and P3 amplitudes negatively related to the length of response distribution tails. We postulate that these results reflect an overactive monitoring system in bilinguals. This enhanced monitoring led to reduced engagement of attentional resources for stimulus categorisation, but also occasionally to slow responses. These results suggest that changes of the cognitive control system due to bilingual experience can change the balance of processes during conflict tasks, potentially leading to a small behavioural disadvantage.