Primary task demands modulate P3a amplitude

Auditory event-related brain potentials (ERPs) were recorded from 10 subjec ts in two different conditions: (1) subjects were required to reorder five visually presented letters in order to form a word and provide a verbal res ponse (task condition); (2) subjects were presented with a control stimulus with the same physical characteristics as the experimental stimulus, but c ontaining just one type of letter (i.e., AAAAA). Subjects had to verbally r espond to such stimuli by saying "A" (control condition). Tones of 1000 Hz (standard) and 1050 Hz (deviant) were also presented to the subjects in a 8 5%-15% probability paradigm 2 s before, during and 8 s after the presentati on of the visual stimuli. Recordings were obtained from Fpz, Fz, Ct and Pt vs. Linked ears. Auditory ERPs to the auditory stimuli after the presentati on of the visual letter string and during the performance of the task were averaged for the standard and deviant tones in both conditions. Only correc t responses were considered for the averages. The N100 was affected by stim ulus type (standard vs. deviant) but not by condition (task vs, control); h owever, larger P3a waves were observed during the control than during the t ask condition. No significant differences between conditions were observed in the mismatch negativity (MMN) latency range. These results suggest that primary task demands modulate involuntary attention processing. (C) 2000 El sevier Science B.V. All rights reserved.