The effect of spatiotemporal displacement on the integration of shape information

Abstract

Within a natural scene it is not uncommon for an object's shape to be revealed over time.We investigated whether the same integration of shape information that happens around a fully visible contour also happens when that information is distributed over time. In a twointerval forced-choice task, observers discriminated between a radial frequency (RF) pattern and a circle that were revealed either using an implicit slit or traced out by a dot's motion; and a line and a modulated line that were either contour-defined or motion-defined. First, with presentation times of approximately 1 s, we found no difference in the strength of integration when comparing a freely visible contour to one that (a) moved behind a slit; (b) was revealed by a moving slit; or (c) revealed piecemeal by a slit appearing at random locations (Experiment 1). Changing the duration of presentation (250-4,000 ms) had no effect on strength of integration or threshold for detection within the moving slit condition (Experiment 2). Considering these results, Experiment 3 revisited integration for a dot tracing out an RF path (Or, Thabet, Wilkinson, & Wilson, 2011), finding removal of a change in speed cue increased the strength of integration to that found in Experiments 1 and 2 of the current study. The pattern of results for modulated lines was different from RF patterns; however, within these conditions, there was no difference in strength of integration between contourdefined and motion-defined stimuli. Our results suggest motion-defined patterns are processed as form from motion.