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Anna Montagnini, Guillaume Masson, Laurent Madelain; Contrast-dependent motion processing : insight from ocular tracking dynamics . Journal of Vision 2014;14(10):490. doi: https://doi.org/10.1167/14.10.490.
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The underestimation of speed for low-contrast, slowly moving objects is a well established phenomenon. Coherently, smooth tracking of low-contrast stimuli is impared both during pursuit initiation (longer latency, Spering et al., 2005) and steady state (lower gain). We have recently probed the dynamic perturbations of steady state pursuit gain during periodic modulations of target-background contrast (using a variant of the Footstep illusion stimulus, Madelain et al, 2013), providing further support for a close relation between motion perception and tracking eye movements across various visual conditions. Importantly, smooth pursuit data allows one to reliably track fine details of the dynamic modulations of visual processing across time. We used a Kanitzsa illusory rectangle as a pursuit target (6°×8°), with the four gray inducers presented at high (100 cd/m2) or low luminance (1 cd/m2) on a yellow bright background (100cd/m2). Subjects tracked the center of the illusory target during a motion ramp at 8°/s. At an unpredictable time (starting with equal probability at 70, 140, 210, 280ms or never wrt target motion onset) the inducers changed luminance (from high to low contrast in the first condition and from low to high contrast in the second condition) for 500ms and then reverse back. We found that the effect of luminance-contrast on steady-state pursuit gain was stronger during the luminance change transitions than with constant luminance. In addition, a very similar dynamic oculomotor pattern was observed for the different onset times of the transient luminance change, arguing against a functional difference of contrast-dependent speed processing for illusory objects between pursuit initiation and the closed-loop phase. Overall these results suggest that contrast-dependent perturbations of velocity estimate depend on the integration of dynamic motion cues in a more complex way than previously thought, possibly taking into account the short term history of visual motion.
Meeting abstract presented at VSS 2014
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