Magnetoencephalographic Correlates of Apparent Motion Illusion of Beta Movement

SUMMARY We examined the underlying mechanisms of the apparent motion illusion of beta movement by obtaining neuromagnetic responses of event‐related fields (ERFs). A simple setting for visual stimulation of two circles, presented 10° apart horizontally, was used in experiment 1. The first circle, with a duration of 16.7 ms, was followed by the second with three conditions of stimulus‐onset‐asynchrony: (a) 16.7 ms, the two circles seen almost simultaneously, (b) 83.3 ms, perceived optimally as beta movement, and (c) 549.8 ms occurring isolatedly. In experiment 2, three conditions of real motion for visual stimulation were set: (a) six circles presented successively for one animation, (b) 14 circles for one animation, and (c) 34 circles for one animation. We applied minimum current estimates (MCEs) to obtain the source activity of the ERFs for beta movement, then calculated an average amplitude for each five 100‐ms epoch after the second stimulus onset in experiment 1, and after the first stimulus onset in experiment 2. As the results, the optimal condition showed maximum activities in the first 100‐ms epoch at the parietal region in experiment 1, suggesting that the motion components of the MCEs were emerging from this epoch. In experiment 2, three conditions of real motion evoked prolonged MCE activities for the temporal and central areas, suggesting that these components were changed with the “speed” of motion perception. The neuromagnetic activities of beta movement and motion perception may originate from parietal areas within 100 ms after the perception of movement.