Beyond habituation: long-term repetition effects on visual event-related potentials in epileptic patients

Sixteen patients with partial epilepsy learned to produce positive or negative slow cortical potential shifts in a biofeedback condition during 20 consecutive training sessions. Visual ERPs to the presentation of the feedback and the discriminative stimulus were recorded at vertex. Regardless of the subjects' task (positivity versus negativity), amplitudes of the P2 (mean peak latency about 225 ms) and P3a (322 ms) components decreased across sessions, resulting in appearance and subsequent enhancement of a negative wave N2 (298 ms) between P2 and P3a. As N2 grew the P2 latency decreased and the P3a latency increased. Additionally, the P3b (472 ms) decreased with repetition, however, it did so slower than P2 and P3a. A comparison between the present data, on the one hand, and those obtained in the ERP habituation paradigm within one session, on the other hand, indicates that some repetition effects cannot be explained by habituation.