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Hiroshi Ashida, Andrew T. Smith; Retinotopic mapping of motion stimuli in human visual cortex. Journal of Vision 2005;5(8):489. doi: 10.1167/5.8.489.
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When a stationary window is filled with a moving texture, the whole window may appear to be displaced in the motion direction (DeValois & DeValois, Vision Res 1991). Curiously, Whitney et al. (Science 2003) found that activation in the visual cortex measured by fMRI shows an opposite shift. But their claim that the retinotopic organization itself is flexible remains controversial because they did not directly compare the spatial activation profiles for motion in the two directions. We presented an annular window with hard edges, in which a concentric sinusoidal grating drifted inward or outward, and measured the fMRI BOLD responses in the occipital lobe of human participants at 3T. A block design was used: inward and outward blocks were interspersed with blocks in which there was no stimulus. For each direction of motion, the difference in activation between motion and blank blocks was mapped onto a cortical flat-map. The representation of stimulus polar angle and eccentricity within each of the first three visual areas was also mapped, using conventional retinotopic mapping procedures conducted in separate scans. The magnitude of cortical activation was then plotted as a function of eccentricity, separately for V1, V2 and V3. Although we replicated the result that activation is stronger near the trailing edge of the moving stimulus than the leading edge, the difference was small and significant shift of the overall spatial distribution was not observed. Instead, the spatial profile of the activation pattern was skewed by motion such that the activation near the trailing edge was enhanced. There was no substantial difference among the visual areas assessed. Gabor stimuli with smooth edges, as used by Whitney et al, yielded very similar results. We confirm that activity in the early visual areas does not explain the perceived shift of stimulus location, but show that retinotopic organization does not change with direction of visual motion.
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