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Daniel Linares, Isamu Motoyoshi, Shin'ya Nishida; A synchronous surround increases motion sensitivity. Journal of Vision 2012;12(9):149. doi: https://doi.org/10.1167/12.9.149.
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Motion sensitivity is often measured using random-dots: some dots (signal) move to the left or to the right while the remaining dots (noise) randomly change position every frame. Sensitivity is estimated as the minimum proportion of signal-dots needed for the observers to discriminate the direction of motion. Although this task is considered to depend on the signal-to-noise ratio, last VSS (Linares, Motoyoshi, Maruya, & Nishida, 2011) we reported that motion sensitivity is doubled when a task-irrelevant surround is presented in synchrony with the motion target. Here, we report some new findings. First, the motion enhancement does not occur when the motion target and the surround are presented for more than about half a second, which suggests that the increase in motion sensitivity occurs at the onset and offset of the stimulus. Second, the motion enhancement is maintained for relatively large separations between the motion target and the surround (about 6 deg), which suggests the involvement of neurons with large surround-suppressed areas like those found in MT and MST. Third, motion sensitivity is enhanced when the surround is composed of one-dimensional bars displayed orthogonally to the direction of motion but not enhanced when the bars are displayed parallel to the direction of motion. In this last situation, the distance of each dot to the bars remains constant during the motion trajectory, which indicates that relative-motion processing is needed to boost motion sensitivity. Our findings support a mechanism that assists the perception of sudden updates of scenes that include a change in the surrounding context, a common situation faced by observers living in dynamic environments.
Meeting abstract presented at VSS 2012
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