Event-related brain potentials dissociate visual working memory processes under categorial and identical comparison conditions

Event-related potentials (ERPs) have been successfully employed to examine the functional and neuronal characteristics of working memory processes. In the present study, we examined the ERP waveforms in a delayed matching tas k to examine the cognitive processes underlying category and identity compa rison and the effects of stimulus complexity. Subjects had to decide whethe r two visual stimuli are (a) physically identical (identical comparison con dition, IC) or (b) identical, irrespective of their orientation (categorial comparison condition, CC). The stimuli were structured five-point patterns , which varied in complexity. For the ERPs elicited during the 1500 ms rete ntion interval, the following pattern of results was obtained: Stimuli in t he CC-condition elicited larger P300 components than in the IC-condition. I n the IC-condition, the P300 was followed by a broadly distributed negative slow wave. Moreover, complex patterns elicited a posteriorily distributed negativity at 350 ms (N350), whereas the less complex patterns gave rise to a fronto-centrally distributed slow wave that started around 500 ms. These results suggest that S1 was more elaborately processed in the CC-condition , while the more complex figures were associated with an early classificati on process during the retention interval. (C) 2000 Elsevier Science B.V. Al l rights reserved.