Event-related brain potentials to irrelevant auditory stimuli during selective listening: effects of channel probability.

The purpose of this study was to identify the cognitive process reflected by a positive deflection to irrelevant auditory stimuli (Pdi) during selective listening. Event-related brain potentials were recorded from 9 participants in a two-channel (left/right ears) selective listening task. Relative event probabilities of the relevant/irrelevant channels were 25%/75%, 50%/50%, and 75%/25%. With increasing probability of the relevant channel, behavioral performances (the reaction time and hit rate) for the targets within the relevant channel improved, reflecting development of a more robust attentional trace. At the same time, the amplitude of the early Pdi (200-300 ms after stimulus onset) elicited by the stimuli in the irrelevant channel with a decreased probability was enhanced in the central region. This positive relation between the strength of the attentional trace and the amplitude of the early Pdi suggests that the early Pdi is elicited by a mismatching between an incoming irrelevant stimulus and an attentional trace.