Speech perception: Single trial analysis of the N1/P2 complex of unimodal and audiovisual evoked responses

Audiovisual speech integration is reflected in the electrophysiological N1/P2 complex. In this study, we analyzed recordings of electroencephalographic brain activity from 28 subjects who were presented with combinations of auditory, visual, and audiovisual stimuli, using single trial analysis based on an independent component analysis procedure. We found that, with respect to the N1/P2 complex, single trials across all subjects and all conditions could be separated into two groups, one with `typical' responses having the same polarity as the average response and another one with `aberrant' responses having opposite polarity. Furthermore, the number of aberrant responses in non-speech interpretation of auditory stimuli was significantly lower compared to speech, which may affect the N1/P2 complex in the ensemble average EP.