Abstract
In biological vision, contextual modulation refers to the influence of a surround pattern on either the perception of, or the neural responses to, a target pattern. One studied form of contextual modulation deals with the effect of a surround texture on the perceived shape of a contour, in the context of the phenomenon known as the shape aftereffect. In the shape aftereffect, prolonged viewing, or adaptation to a particular contour’s shape causes a shift in the perceived shape of a subsequently viewed contour. Shape aftereffects are suppressed when the adaptor contour is surrounded by a texture of similarly-shaped contours, a surprising result given that the surround contours are all potential adaptors. Here we determine the motion and temporal properties of this form of contextual modulation. We varied the relative motion directions, speeds and temporal phases between the central adaptor contour and the surround texture and measured for each manipulation the degree to which the shape aftereffect was suppressed. Results indicate that contextual modulation of shape processing is selective to motion direction, temporal frequency and temporal phase. These selectivities are consistent with one aim of vision being to segregate contours that define objects from those that form textured surfaces.
Highlights
We found that for globally drifting contours, TSSCS was maximal when the surround and center adaptor contours were moving in the same direction, at the same speed and at relatively high speeds, while for locally moving stimuli, the suppression was unaffected by the relative motion direction between center and surround
TSSCS was found to be selective for temporal frequency and temporal phase, and broadly tuned to the temporal phase-difference between central contour and surround texture
Taken together our results suggest the involvement of both feed-forward and feedback pathways: V1 neurons with ERFs feed-forwarding their responses into shape-selective neurons in areas such as V4, with feedback from MT and/or MST. These dynamic properties of TSSCS play an important role in extracting contours that define objects from those that define textured surfaces
Summary
Eight observers participated in this study, the two authors and six observers who were naive with regard to the experimental aims. Three participants took part in Experiment [1, 3, 4] and four in Experiment 2. All observers had normal or corrected-to-normal visual acuity. Observers gave their written informed consent prior to participating in this study and were treated in accordance with the Declaration of Helsinki.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
