Abstract: A stimulus-stimulus and stimulus-response compatibility task was used to investigate to what extent ADHD children had deficits in conflict control at periods of perceptual processing and response activation, and whether they resolved conflicts in similar time courses as normal children. Subjects were two subtypes of ADHD children (25 predominantly inattentive and 30 combined) and normal controls who were matched in age, IQ and the year of education. Results showed that ADHD children had great difficulties (even more sever showed the combined comparing with predominantly inattentive) in resolving conflict at period of response while they showed a normal pattern as controls in controlling conflict at period of perception. Moreover, for both ADHD and normal children, resolution of conflicts at period of perceptual and response had different time courses, with more time needed for the resolution of response conflict

Key words: conflict control, periods of processing, subtypes of ADHD