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Interaction of color-defined and luminance-defined motion signals in human visual cortex

26.432, Saturday, 17-May, 2:45 pm - 6:45 pm, Banyan Breezeway
Session: Motion Perception: Neural mechanisms

Ichiro Kuriki1,2, Hongfei Xie2, Rumi Tokunaga1,2, Kazumichi Matsumiya1,2, Satoshi Shioiri1,2; 1Research Institute of Electrical Communication, Tohoku University, 2Graduate School of Information Sciences, Tohoku University

It has been tested by motion aftereffect in a psychophysical study that color-defined and luminance-defined motion signals can interact. We tested direction selective aftereffects of color-defined and luminance-defined motions by psychophysics and fMRI to investigate its neural correlate. We used a ring-shaped stimulus with sinusoidal modulation, which moved in either clockwise (CW) or counter-clockwise (CCW) direction at the speed of 1/6 rotation-per-second; temporal frequency of the contrast modulation was 1 Hz, since the spatial modulation of the radial pattern was 6 cycles-per-round. There were four combinations for adaptation and test stimuli: color/luminance × CW/CCW. Color stimuli were adjusted subjectively to be isoluminant in each subject. The subject adapted to one direction of motion, defined by either color or luminance, during an experimental run. The duration of initial adaptation was 27 s, and the durations of top-up adaptation were randomly jittered between 12 ± 3 s. The test stimulus was randomly selected among the four combinations (color/luminance × CW/CCW), and was presented for 3 s between the continuous adaptation stimuli. Subjects performed a direction-discrimination task for the test stimulus, in addition to a fixation point task conducted throughout the run by counting the number of changes to a particular color. Psychophysical results were evaluated by the difference of reaction times to the test stimuli in the same and opposite direction of adapting stimulus, and cross-adaptation effects between color and luminance motions were confirmed. The direction selectivity of fMRI results was evaluated in each visual area ROIs with the difference in the BOLD-response amplitudes to the two directions of test-stimulus motion. Cross adaptation effects were found at 3-9 s after the onset of the test stimulus in most visual areas, while MT+ exhibited uncrossed aftereffect. The details and possible mechanisms of crossed adaptation effects will be discussed in the presentation.

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