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Robert F. Hess, Tim Ledgeway; Direction- and speed-defined spatial contours; one mechansim or two?. Journal of Vision 2002;2(7):121. doi: 10.1167/2.7.121.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose. The visual system integrates local orientation information across space to define spatial contours (Field, etal V.R. 33, 1993). More recently, it has been shown that a similar integration occurs for the direction of local motion signals in different parts of the field if they are aligned along a spatial contour (Ledgeway & Hess ARVO, 2001). Here we ask whether similar spatial-linking rules hold for contours defined by a common speed different from that of the background. Methods Using a standard 2AFC task, observers were asked to choose which interval contained the elongated contour (path). One interval chosen at random on each trial contained 158 micropatterns of random position and direction (background micropatterns) and in the other interval (path plus background)the motion directions of some (8) of the background micropatterns were arranged to lie along the invisible backbone of an elongated contour. The directions/speeds of motion of the micropatterns making up this contour could be varied independently from those of the background micropatterns. Performance was measured for direction-defined or speed-defined contours of varying straightness.Results The results for speed-defined paths do not follow the specialized rules for detecting or disambiguating 2-D spatial contours because they do not depend on the curvature of the contour to be detected and operate under conditions where directional-linking has been rendered ineffective (e.g. when all motion directions are either random or all the same. Conclusions The results show that while speed does enhance performance for motion-defined contours, it does so via a different route to that of directional-linking. For motion-defined contours, the Gestalt notion of “common fate” and “good continuity” occur via separate underlying mechanisms.
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