Abstract
Alternations between bound and unbound motion perception of “aperture stimuli” occur either spontaneously or through external change of critical stimulus parameters known to yield hysteresis. We recorded the transition dynamics of bound and unbound percepts using simple shapes viewed through apertures, and compared these dynamics in conditions of fixation and oculomotor pursuit. Perceptual alternations were induced at a slow rate (0.03 Hz) by smoothly changing parameters known to influence motion binding -contrast, shape, motion noise- or occurred spontaneously with an unchanging stimulus. A red dot, moving in phase with the center of the “aperture stimulus” or kept stationary in the center of the display, was provided as a target to the oculomotor system. The results indicate different transition dynamics in the “eyes static” and “eyes moving” conditions, revealing either the influence of minimized retinal slip or a more general perception/action coupling mechanism. Disentangling these different possibilities was done by varying the phase lag of the target dot relative to the “aperture stimulus”. Overall, the data indicate that spontaneous and induced perceptual transitions occur in the “eyes moving” conditions, despite the fact that the retinal slip was minimized by accurate tracking. However, the amplitude of hysteresis and the duration and frequency of alternations is altered by pursuit eye movements, with shorter episodes of unbound percept. The results are discussed in the light of the proposed perception/action dichotomy.