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Javier O. Garcia, John A. Pyles, Emily D. Grossman; Neural correlates of degraded complex motion perception. Journal of Vision 2006;6(6):1037. doi: 10.1167/6.6.1037.
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© ARVO (1962-2015); The Authors (2016-present)
Background. Visual information is largely processed via two parallel pathways: one specialized for motion information (M-pathway) and the other specialized for form information (P-pathway). By manipulating luminance and color contrast, we altered the contribution of the M-pathway, thereby systematically degrading perception of simple and complex motion, and measured the corresponding changes in neural responses. Our analysis targeted several brain areas including MT+ and STSp (a brain area selective for complex, biological motion). Method. In a blocked fMRI experiment, observers viewed animations depicting three types of motion of varying levels of complexity: (1) coherent motion in random dot kinematograms (RDKs), (2) collinear triplets masked in fixed-path noise, and (3) biological motion (Johansson, 1973) masked in vector-matched noise. Displays were rendered as yellow dots on a gray background. Luminance contrast was set at 10%, 5% or 0% (defined perceptually as the point of perceived isoluminance). Coherence levels (RDKs) and number of masking dots (collinear triplets and biological motion) were fixed individually to ensure threshold (82%) performance for each level of contrast. Results. Neural responses in MT+ were largely contrast-dependent with the exception of the coherent motion RDKs, for which BOLD levels also depended on coherence. BOLD responses in STSp maintained biological motion-selectivity, regardless of luminance contrast. Conclusions. These results demonstrate the relative contributions of the M-pathway to the global neural responses of motion-driven cortical areas, and a competitive interaction between stimulus properties, such as coherence, contrast and complexity.
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