The role of eye movements and masking in monocular rivalry

Using an image stabilization technique, we have examined the role of eye movements on the phenomenon of monocular rivalry. Cross-correlation analysis confirms that perceptual onset of the vertical grating coincides with perceptual disappearance of the horizontal (and vice versa). Vertical and horizontal retinal image motion can modulate, selectively, the visibility of the horizontal and vertical gratings. However, a stable percept was observed when constant retinal image motion was matched for both vertical and horizontal components. These results support an eye-movement and afterimage explanation for the phenomenon of monocular rivalry (Georgeson, 1984). However, in addition to enhancing the visibility of a horizontal grating, a vertical "saccadic-like" retinal image motion decreased the visibility of the vertical component. This result is consistent with rivalry. That is, the visibility of both gratings are not independent, but are inversely related to each other. Our results are inconsistent with a hypothesis for monocular rivalry based upon inherently unstable neural interactions, but they also show that unstable fixational eye movements and afterimages are not the only factors determining the perceptual fluctuations.