Noninvasive studies on intrinsic alternation of perceived images in binocular rivalry based on high-resolution EE

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In an attempt to detect the neural processes related to endogenous alternation of perceived images in binocular rivalry (BR), we have studied ERPs in ten healthy subjects. Vertical and/or horizontal gratings were presented to the left and right eyes separately. Subjects were instructed to press a button when perceived gratings changed. This triggered data acquisition. As a control experiment (Control 1), identical vertical (or horizontal) gratings were presented to both eyes and were changed to horizontal (or vertical) gratings. In this experiment subjects pressed a button when the perceived gratings were changed. In the second control experiment (Control 2), subjects pressed a button voluntarily at random moments while identical gratings were presented continuously. A broad negative component beginning at -400 ms and lasting until O ms was observed in the left parietal, left posterior-temporal and left occipital areas in BR. A prominent negative component peaking at -55 ms was observed centered in the parietal area. However, no corresponding component was observed in Control 2. Since the perceived image did not change in Control 2, the negative component observed in BR may reflect a neural process related to awareness of changes in perceived images.Furthermore, we have measured and analyzed eye movements and subjects' button pressed data simultaneously in BR. A pair of vertical gratings drifting to opposite horizontal direction were presented to the left and right eyes separatory in BR. As a control experiment, the same data were measured in a binocularly fused condition (BF). It was found that the change in optokinetic nystagmus (OKN) occurred earlier than the button press in BR. The delay time of button press from the change in OKN in BR was significantly larger than that in BF. Individual difference in the change in OKN was smaller than that of button press.