Reversal-rate dependent differences in the EEG gamma-band during multistable visual perception

It is an often reported observation in the literature on multistable percep tion that the reversal rate within a given observation time is subject to a high interindividual variability. Recently, we reported frontal gamma-band enhancement during multistable visual perception. The aim of the present s tudy was to investigate whether changes in the gamma-band correspond to the variability of the reversal rate. Therefore, a total of 25 observers were divided into two subgroups according to their reversal rate during a 400-s observation period of a reversible pattern based on apparent motion. Subjec ts with more than 40 reversals within the 400-s were defined as high-rate s witchers (HRS). Subjects with a reversal rate below 40 switches were define d as low-rate switchers (LRS). EEG was recorded from frontal, central, pari etal, and occipital locations of both hemispheres. The results showed signi ficantly higher gamma activity for the HRS in both phase-locked and non-pha se-locked oscillations. Both subgroups showed the highest gamma amplitudes at frontal locations. The results support the involvement of attentional to p-down processing in figure reversal. It is concluded that the higher gamma activity for the HRS reflects states of higher arousal, alertness and/or a ttention according to their fast reversal rate. (C) 2000 Elsevier Science B .V. All rights reserved.