Abstract
We exposed the visual system to four different stimuli that can induce bistable perception. The bistability paradigms that we used were slant rivalry, Necker cube rivalry, grating rivalry and house-face rivalry. For each of these stimuli we investigated the role of eye movements for perceptual alternations from one to the other representation. We compared results when subjects were trying to hold one of the two percepts with results when subjects did not try to actively influence the percept (natural viewing condition). The results show that, for each paradigm, saccades are suppressed just after a perceptual alternation occurs in the natural viewing condition. For slant rivalry, there is no positive correlation between saccades and a perceptual alternation before the perceptual alternation. For Necker cube rivalry and binocular grating rivalry, saccades sometimes occur before the perceptual alternation, but this positive correlation is relatively small. For house-face rivalry the positive correlation between saccades and perceptual alternations before the alternations is more pronounced. When subjects are trying to hold a percept any correlation between saccades and perceptual alternations is reduced. Average gaze positions and average horizontal vergence do not change at the time of a flip for all stimuli in all viewing conditions. However different voluntary control conditions can lead to different average fixation positions or a wider scatter of fixations. We conclude that generally eye movements are not necessary to exert voluntary perceptual control.