Interactions among variables in the P300 response to a continuous performance task in normal and ADHD adults.

This study investigated the effect of variable interstimulus intervals (ISIs) in a group of normal and ADHD (attention deficit hyperactivity disorder) adults on behavioral reaction time and the auditory P300 event-related potential. This study involved 20 adult subjects with no history of ADHD and 11 adult subjects diagnosed with ADHD. The subjects were instructed to respond to the common stimuli and ignore the rare stimulus. Significant differences in the latency of the P300a, P300b, the amplitude of the P300b, and in the number of false alarms and correct rejections between ISIs were observed in the normal group. The group with ADHD failed to show any significant differences between ISIs. Psychophysical measures of hits showed significant differences for the number of hits for ISI 2 (2 sec) between the two groups. False alarms and correct rejections for all ISIs showed significant differences between groups. Significant group differences were seen for latency of the P300a and P300b at each of the three ISIs, for amplitude of the P300a and P300b for ISI 1 and ISI 3, and for the amplitude of the P300b for ISI 2. There was a greater separation in the group with ADHD between the P300a and P300b suggesting a processing lag in that group.