Abstract
The evoked magnetic field (magnetoencephalogram: MEG) was measured in human subjects observing random-dot motion. 600 random dots generated with VSG2/3 (Cambridge Research Systems) moved at about 10 deg s−1 (either in the 45° or the 135° direction). The motion frame (5 s) was followed by a stationary frame on a screen (projected from Barcodata 3100 projection system) subtending a visual angle of about 20 deg × 20 deg. Six subjects observed the motion frame presented in the left visual field. The magnetic evoked field (80 averagings) was measured from 37 points over occipital, temporal, and parietal areas (Magnes SQUID biomagnetometer, BTi) of the right brain hemisphere. Dipole estimates based on equal magnetic field contours (190 ms after motion frame onset with value of goodness of fit greater than 0.95) and MRI image fitting (sagittal, coronal, and axial view) for each subject suggest that the main loci subserving motion perception lie in the surrounding region over occipital, temporal, and parietal junction areas in the human brain close to area MT.
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