The spatial origin of a perceptual transition in binocular rivalry

Abstract

When the left and the right eye are simultaneously presented with incompatible images at overlapping retianl locations, an observer typically reports perceiving only one of the two images at a time. This phenomeneon is called binocular rivalry. Perception during binocular rivalry is not stable; one of the images is perceptually dominant for a certain duration (typically in the order of a few seconds) afer which perception switches towards the other image. This alternation between perceptual dominance and suppression will continue for as long the images are presented. A characteristic of binocular rivaly is that a perceptual transition from one image to the other generally occurs in a gradual manner: the image that was temporarily suppressed will regain perceptual dominance at isolated locations within the perceived image, after which its visibility spreads throughout the whole image. These gradual transitions from perceptual suppresion to perceptual dominance have been labeled as travelling waves of perceptual dominance. In this study we investigate whether stimulus parameters affects the location at which a traveling wave starts. We varied the contrast, spatial frequency or motion speed in one of the rivaling images, while keeping the same parameter constrant in the other image. We used a flash-suppresion paradigm to force one of the rival images into perceptual suppresion. Observers waited until the suppressed image became perceptually dominant again and indicated the position at which this breakthrough from suppression occurred Our results show that the starting point of a travelling wave during binocular rivaly is highly dependent on local stimulus parameters. More specifically, a traveling wave most likely started at the location where the contrast of the suppressed image was higher than that of the dominant one, the spatial frequency of the suppressed image was lower than that of the dominant one, and the motion speed of the suppressed image was higher than that of the dominant one. We suggest that a breakthrough from suppression to dominance occurs at the location where salience (the degree to which a stimulus element stands out relative to neighboring elements) of the suppressed image is higher than that of the dominant one. Our results further show that stimulus parameters affecting the temporal dynamics during continuous viewing of rival images described in other studies, also affect the spatial origin of traveling waves during binocular rivalry. © 2008 Paffen et al.