P3a from a passive visual stimulus task

Objective: Visual event-related brain potentials (ERPs) were elicited using a 3-stimulus oddball paradigm to assess the P3a with passive stimulus processing. Methods: Young adults (n=12) were presented with a series of visual stimuli consisting of a solid circle standard stimulus (P=0.76) that was difficult to discriminate from a larger target circle (P=0.12), with a large square distractor stimulus (P=0.12) presented randomly in the series. Subjects were instructed in the passive condition to simply look at the stimuli and in the active condition to press a mouse key only to the target stimulus. ERPs were recorded from 15 scalp electrodes, with the amplitude and latency of the P300 from the distractor and target stimuli assessed. Results: The P3a from the distractor stimulus was similar in amplitude, scalp topography, and peak latency across the passive and active task conditions. The P3b from the target stimulus demonstrated much smaller amplitude, highly altered scalp topography, and longer latency for the passive compared to active task conditions. Conclusions: The P3a can be obtained with visual stimuli in the 3-stimulus paradigm under passive viewing conditions. Theoretical implications and clinical applications are discussed