Recognition of direction of uniform and accelerated visual motion and EEG alpha wave phases.

The perception of visual motion in seven subjects was studied comparing motion towards or away from the fixation point in the left or right hemifield. The light target was moved either at a constant velocity or positively or negatively accelerated to compensate for the magnification factor of the visual cortex. We compared probability and latency of motion recognition when it was asynchronous or synchronized to different phases of the alpha wave of the EEG recorded over the occipital cortex. If the motion accelerated away from the fixation point and was synchronized with the alpha wave it was more likely to be perceived whereas if it was towards the fixation point it was less likely to be detected. However, perception of the constant velocity motion was not changed by locking it to the alpha wave phase. These results support the hypothesis that the scanning waves of excitation spread over the visual cortex periodically and that they are locked to the alpha component of the EEG.