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Hiromasa Takemura, Hiroshi Ashida, Kaoru Amano, Akiyoshi Kitaoka, Ikuya Murakami; Neural correlates of induced motion revealed by fMRI.. Journal of Vision 2012;12(9):755. doi: https://doi.org/10.1167/12.9.755.
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© ARVO (1962-2015); The Authors (2016-present)
A physically stationary stimulus appears to move in the direction opposite to surrounding motion (induced motion). Although previous studies have argued similarities between induced motion and surround suppression of direction-selective neurons in macaque areas MT and MSTl, the relationship between subjective perception of induced motion and cortical responses is still unknown. We addressed this issue by using functional magnetic resonance imaging (2-mm isotropic voxels, TR = 3 s) for human subjects. Visual stimuli were composed of a central Gabor patch surrounded by an annulus filled with a translating random-dot pattern (inducer). We examined how cortical activations differed depending on the velocity of the central stimulus; the velocity of the inducer was constant across conditions. The direction of the whole stimulus was changed every second within a 15-s stimulus block, each of which was sandwiched by rest blocks containing only the fixation point. We defined V1, V2, V3, and hMT+ based on activations in separate retinotopy and localizer scans, and determined the region of interest within each area by selecting voxels that showed significant responses to dynamic random-noise covering the central stimulus region. We found that hMT+ exhibited the greatest activation when the central stimulus moved fast in the direction opposite to that of the surround. More importantly, the hMT+ activation was the smallest when the central stimulus moved at the psychophysically determined cancellation velocity, at which induced motion was subjectively canceled. This pattern was consistently found in the two subregions of hMT+, namely TO-1 and TO-2 (Amano et al., 2009). Although V1, V2, and V3 showed similar patterns of activation, the compatibility with the pattern of induced motion perception was most pronounced in hMT+. The present results suggest that hMT+ is one of the neural correlates of induced motion perception and important for extracting object motions from a noisy background.
Meeting abstract presented at VSS 2012
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