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Carole Filangieri, Andrea Li; Position selectivity of mechanisms underlying the perception of 3D shape from orientation flows. Journal of Vision 2011;11(11):50. doi: 10.1167/11.11.50.
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Previously, using the psychophysical technique of selective adaptation, we've provided evidence for extra-striate 3D shape-selective neural mechanisms that are invariant to texture pattern (Filangieri & Li, 2009). This was done by eliciting negative 3D shape aftereffects from stimuli in which the 3D concave or convex shape was defined by luminance-modulated, contrast-modulated, and illusory orientation flows. The goal of the current experiment was to test whether 3D shape-selective mechanisms are invariant to the exact retinal position of the stimulus. If these mechanisms are position-invariant, we would expect negative shape aftereffects even when the adapting and test stimuli are misaligned in space. We tested for shape aftereffects using horizontally sinusoidally corrugated stimuli in which the 3D concave or convex shape was conveyed by luminance-modulated orientation flows. Adapting and test stimuli were misaligned horizontally by 2 degrees such that the corrugations of adapting and test stimuli were 180 degrees out of phase. In a separate control condition, adapting and test stimuli were misaligned vertically by 2 degrees such that the corrugations of adapting and test stimuli were in phase. As expected, our results show negative shape aftereffects in the vertical conditions we tested. We also found evidence for positive shape aftereffects in the horizontally misaligned conditions that are consistent with adaptation of position-selective mechanisms. Together, these results suggest that 3D shape-selective mechanisms that respond to luminance-modulated orientation flows appear to be sensitive to shifts in position of 2 degrees, which in our experiment span a single convexity or concavity. Preliminary results in an additional experiment suggest that this position-selectivity may extend to neural mechanisms sensitive to orientation flows defined by contrast modulated and illusory orientation flows.
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