視覚誘発電位と脳磁図を用いた，運動定義形状知覚の処理機序の解析

摘要

Motion-defined pattern perception includes two perceptions: motion and pattern perception. The purpose of this study was to clarify the difference in time courses and activated areas between motion detection and pattern perception. Psychophysical experiments were carried out by employing a random dot kinematogram to ask the direction of a coherently moving dot in a core rectangle toward upper left or lower right (a direction discrimination task), and the shape of that rectangle oblong vertically or horizontally (a pattern discrimination task) by varying dot velocity in four levels (14.4, 28.8, 43.2 and 57.6 deg/s). When the stimuli were presented in the lower half of visual field, the mean correct rate of ten participants for both motion and pattern was larger than 0.75 (the psychophysical threshold of perception) at the velocity of 14.4 deg/s, whereas at the velocity of 43.2 deg/s, only that of motion perception exceeded the threshold. When the magneto-encephalogram (MEG) and visual evoked potential (VEP) were measured with similar stimuli, the root mean square (RMS) of MEG difference between 14.4 deg/s and 43.2 deg/s was explicitly elevated at the latency from 250 ms to 290 ms. This result was consistent with those in the previous study, demonstrating that the peak of VEP at around 290 ms were a common phenomenon elicited by every type of figure perception. The multi dipole (2-dipoles) estimation of MEG at this latency revealed that the activated areas for the pattern perception were located in both ventral and dorsal portions of the occipital cortex, while the motion perception activated the dorsal portion of occipital cortex alone.