Auditory Language Comprehension During Saccadic Eye Movements: An Investigation Using the N400 Event-Related Brain Potential

In many situations of everyday life, it is important to quickly understand a spoken message despite distraction by an already ongoing activity. Previous dual-task studies recording the N400 component of the event-related potential (ERP) have shown that auditory language comprehension can be strongly delayed by temporally overlapping additional tasks. In the current study, we investigated whether this interference is aggravated by the need for saccadic eye movements and visuospatial attention shifts in the overlapping task. In two dual-task experiments, a synonymy judgment task for spoken words was combined with a visual discrimination task at different stimulus onset asynchronies. In half of the trials, the primary visual task required a 10° exogenous saccade towards a peripheral stimulus. The timing of semantic processing in the secondary task was assessed by recording the N400. We replicated that with increasing temporal overlap between the tasks, the N400 component was strongly delayed. However, additional saccade-related processes in the primary task had no detrimental effects on concurrent spoken language processing on their own. Unexpectedly, we also observed that a preceding saccade consistently facilitated subsequent motoric processing in the visual task (as indexed by manual reaction times and the lateralized readiness potential), suggesting that saccade execution as such can significantly enhance subsequent processing.