Lateralized irrelevant speech alters visuospatial selective attention mechanisms.

Recent studies indicate that the coordination of spatial attention across modalities may in part be mediated by a supramodal attentional system. We try to extend the concept of a supramodal system and hypothesized that involuntary modulations of auditory attentional processes by irrelevant speech signals influence visuospatial attention, suggesting crossmodal links between vision and speech. In order to test this we recorded event-related brain potentials (ERPs) of 12 healthy subjects in a visuospatial selective attention task. The task to identify target stimuli appearing at lateral visual field locations caused the expected enhancements of the early P1 and N1 ERP components to attended visual stimuli. Understandable and ununderstandable task irrelevant speech was presented either at the visually attended position or in the opposite visual field location. Speech contralateral to unattended visual stimuli led to a decreased N1 amplitude. This effect was stronger for understandable speech. Thus, speech influences the allocation of visual spatial attention if it is presented in the unattended location. The results suggest crossmodal links of speech and visuospatial attention mechanisms at a very early stage of human perception.