Blake, R. (1998). What can be "perceived" in the absence of visual awareness? Current Directions in Psychological Science, 6, 157-162.

This article is a short review of the literature on binocular rivalry, which occurs when each eye alternates its dominance in viewing competing stimuli (i.e., when each eye views a dissimilar image). Interestingly, as Blake point outs, "during binocular rivalry, a normally visible, potentially interesting monocular stimulus may be suppressed from conscious awareness for several seconds at a time while the other eye is dominant" (pp. 157-158). The question that the author addresses is, essentially, in the absence of the stimulus from conscious awareness, what neural information, if any, is perceived by the brain? To answer this question, Blake and his associates have sought to identify which elements of visual information processing continue to operate during such "rivalry suppression."

IV. General Method:

To study rivalry suppression, Blake has used protocols involving visual adaptation and aftereffects, priming, and cued visual attention procedures. Visual adaptation procedures involve a subject viewing a particular visual stimulus for a prolonged period and often gives rise to an illusory aftereffect image. Priming entails exposing subjects to a particular visual stimulus before being exposed to other, usually similar, visual stimuli. The effect of this procedure is to make it easier for subjects to see these other stimuli. Finally, cued visual attention procedures involved the presentation of cues that signal the presentation of visual stimuli.

V. Conclusions and Implications:

Blake' research shows that (1) rivalry suppression produces decreased magnitudes of visual aftereffects, especially during adaptation to complex movement; (2) some forms of priming are susceptible to rivalry suppression; and (3) attentional cues probably do not operate during rivalry suppression. Thus, at least in some situations, visual stimuli can be perceived outside of conscious awareness, a finding that, as Blake points out, underscores the utility of using binocular rivalry to explore the neural correlates of visual information processing.