Event-related potentials and audiovisual stimuli: multimodal interactions.

In a discrimination task event-related potentials (ERPs) were recorded in human participants to simultaneously presented visual and auditory stimuli with relevant and irrelevant auditory and visual features. Stimuli consisted of combinations of a sine-wave tone (either target or non-target frequency) and a rectangle of particular (target or non-target) orientation. In two conditions either the auditory or the visual discrimination was easier. Stimuli with just one target feature elicited attention-related ERP components (selection negativity and N2b in the visual, and N2b in the auditory modality) only if that feature could be easily discriminated. This finding shows the hierarchical organization of attentional processing of auditory and visual features. Target stimuli in both conditions elicited visual and auditory attention-related components. This finding, together with the similarity of ERPs to stimuli without target features suggest, that these components cannot be considered as on-line correlates of elementary discrimination processes.