Voluntary alteration of pattern visual evoked responses.

Pattern and flash visual evoked responses (VERs) were recorded from a large group of ophthalmologically normal subjects during two conditions: in one they were instructed to attend to the stimulus and in the other they were instructed to ignore the stimulus but maintain their gaze on the stimulus. Pattern VERs were recorded from 42 subjects. Fixation was constantly monitored during both attend and ignore conditions and no changes of fixation were noted at any time. The amplitude of the major positive wave of the pattern VERs produced by both 50- and 25-min checks was reduced significantly during the ignore condition. The implicit time of this positive wave did not differ significantly during the two conditions. The pattern VERs of eight subjects were extinguished and the VERs of another three subjects were unrecognizable during the ignore condition. Flash VERs produced by 10 flashes per second were recorded from 38 of the 42 subjects. There were no significant differences between the amplitudes recorded during the attend and ignore conditions.