Dynamics of perceptual filling-in of visual phantoms revealed by binocular rivalry.

How do selective and constructive visual mechanisms interact to determine the outcome of conscious perception? Binocular rivalry involves selective perception of one of two competing monocular images, whereas visual phantoms involve perceptual filling-in between two low-contrast collinear gratings. Recently, we showed that visual phantoms lead to neural filling-in of activity in V1 and V2, which can be dynamically gated by rivalry suppression (M. Meng, D. A. Remus, & F. Tong, 2005). Here, we used psychophysical methods to study the temporal dynamics of filling-in, by applying rivalry or flash suppression to trigger the suppression or appearance of visual phantoms. Experiments revealed that phantom filling-in involves an active, time-dependent process that depends on the phenomenal visibility of the phantom-inducing gratings. Shortly after the inducing gratings became dominant during rivalry, the likelihood of perceiving phantoms in the intervening gap increased over time, with larger gaps requiring more time for filling-in. In contrast, suppression of the inducing gratings promptly led to the disappearance of visual phantoms, with response times independent of gap size. The fact that binocular rivalry can prevent the formation of visual phantoms rules out the possibility that rivalry suppression occurs after the site of phantom filling-in. This study provides novel evidence that visual phantoms result from a slow time-dependent filling-in mechanism; possible models to account for its time course are discussed.