Competition for consciousness among visual events: The psychophysics of reentrant visual processes.

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Abstract
Advances in neuroscience implicate reentrant signaling as the predominant form of communication between brain areas. This principle was used in a series of masking experiments that defy explanation by feed-forward theories. The masking occurs when a brief display of target plus mask is continued with the mask alone. Two masking processes were found: an early process affected by physical factors such as adapting luminance and a later process affected by attentional factors such as set size. This later process is called masking by object substitution, because it occurs whenever there is a mismatch between the reentrant visual representation and the ongoing lower level activity. Iterative reentrant processing was formalized in a computational model that provides an excellent fit to the data. The model provides a more comprehensive account of all forms of visual masking than do the long-held feed-forward views based on inhibitory contour interactions. From the time a stimulus first enters the eye to the time a percept emerges into consciousness, the initial stimulus has been coded at several levels in the visual system. One of the main goals in studying visual information processing is to specify the represen- tations at each level and the temporal sequence between them (Lachman, Lachman, & Butterfield, 1979). Historically, that se- quence was regarded as being mainly feed forward, with process- ing advancing from simple to increasingly complex attributes, along brain pathways that converge to a common area in which conscious perception occurs. Here, we present an alternative ap- proach, one more in keeping with recent advances in visual neu- rophysiology. Because we now know that reentrant signals are a major form of communication between brain regions, it is time to begin making explicit use of reentrant processing in theories of perception. To show that this can be done effectively in one domain, we report on a series of psychophysical experiments involving visual masking. In our view, a similar approach could be adopted in other areas of visual perception, especially those in which temporal aspects of processing are at issue.

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