Cortical Dynamics of Form and Motion Integration: Persistence, Apparent Motion, and Illusory Contours
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How does the visual system generate percepts of moving forms? How does this happen when the forms are emergent percepts, such as illusory contours or segregated textures, and the motion percept is apparent motion between the emergent forms? We develop a neural model of form-motion interactions to explain and simulate parametric properties of psychophysical motion data and to make predictions about how the parallel cortical processing streams Vl→MT and Vl→V2→MT control form-rotation interactions. The model explains how an illusory contour can move in apparent motion to another illusory contour or to a luminance derived contour; how illusory contour persistence relates to the upper ISI threshold for apparent motion; and how upper and lower ISI thresholds for seeing apparent motion between two flashes decrease with stimulus duration and narrow with spatial separation (Korte's laws). The model accounts for these data. by suggesting how the persistence of a. boundary segmentation in the Vl→V2 processing stream influences the quality of apparent motion in the Vl→MT stream through V2→MT' interactions. These data may all be explained by an analysis of how orientationally tuned form perception mechanisms and directionally tuned motion perception mechanisms interact.