Perceptual change in response to a bistable picture increases neuromagnetic beta-band activities

The purpose of the present study was to examine by whole-head magnetoencephalography (MEG) brain oscillatory responses related to visual perceptual change of short-term duration in the absence of morphologic change. Twenty healthy volunteers participated in this study. We used three pictures: a bistable picture with ambiguous contours that could represent two different objects ('target') and two preceding pictures that were clear representations of either object ('face' or 'saxophone'). Two types of stimulus conditions were created, the 'face-target' (F-T) condition and the 'saxophone-target' (S-T) condition, and data acquisition was performed mainly during presentation of the 'target' picture. Time-frequency analysis was performed by means of fast Fourier transform. All subjects reported that they perceived the 'target' picture predominantly as a 'face' regardless of the preceding picture. We suspect that perceptual change occurred more frequently in the S-T condition than in the F-T condition. We found significantly greater synchronization in the beta (14-30-Hz) frequency band, ranging from 250 to 450ms predominantly over the occipital and parietal regions, after stimulus alternation for the S-T condition than for the F-T condition. Results of the present study show that the change in beta-band activity reflects a change in visual perception.