Local motion-contrast Interactions Influence Global Shape Perception
26.447, Saturday, May 11, 2:45 - 6:45 pm, Orchid Ballroom
Gennadiy Gurariy1, Gideon Caplovitz1; 1Psychology, University of Nevada, Reno
The perception of objects in the world depends upon the successful integration of form and motion into a unified neural representation and has traditionally been thought to occur through separate pathways. However, it has recently been shown that that these processes may interact in complex ways. The perceived global shape of an object is dictated by the spatial relationships of its local constituents and can be influenced by physical speed. Recent work has demonstrated that shape distortions can be perceived even when speed is held constant. For example, the perceived speed of local constituents was shown to be influenced by their orientation relative to their direction of motion and subsequently led to global shape distortions. Here, we investigate whether other local modifications, specifically luminance contrast, can alter perceived speed and also influence global shape. It has been previously demonstrated that the subjective perception of an objects velocity slows down as a function of reduced contrast. Utilizing the method of constant stimuli, we presented stimuli consisting of four Gaussian blobs arranged to form the corners of a rectangle which varied across different aspect ratios and traversed either the vertical or horizontal axis. Participants were asked to make a judgment concerning the orientation of the rectangle as being vertical or horizontal. If perceived speed influences global shape then we would predict global extension or compression from lowering the contrast in trailing or leading edge blobs, respectively. Our results were consistent with this hypothesis, specifically, the leading edge blobs with reduced contrast appeared to move slower resulting in the global shape appearing more compressed relative to either lowered contrast trailing edge or full contrast conditions. In conclusion, our study supports the hypothesis that form and motion are not disjoined and that perceived speed can be contingent upon the local degree of contrast.