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Lee A. Gilroy, Randolph Blake; Negative afterimages generated during binocular rivalry show signs of weakness and signs of strength. Journal of Vision 2005;5(8):1. doi: 10.1167/5.8.1.
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© ARVO (1962-2015); The Authors (2016-present)
In a series of experiments we investigated the interaction between binocular rivalry and static, negative afterimages (AIs). In experiment 1, one eye was exposed to a static grating that was never consciously experienced by the observer, because this grating remained suppressed in rivalry throughout the entire exposure period (the dominant stimulus itself was designed to preclude formation of an AI). As expected, the suppressed grating generated a vivid AI whose orientation could be accurately identified; not surprisingly, the strength of this AI varied with induction contrast. Surprisingly, however, Experiment 2 revealed that the strength of this afterimage was significantly weaker than the AI produced by that same stimulus when it was visible throughout the entire induction period. Suppression weakens AI formation, implying that at least some component of AI induction is cortical (Shimojo, et al., 2001, Science) and therefore susceptible to rivalry suppression, itself a cortical process. In Experiment 3, dichoptic, orthogonally oriented grating AIs were generated; flash suppression (Wolfe, 1984, Vis. Res.) was used to ensure that one of the two gratings was exclusively dominant during the induction phase. As expected from earlier work (Blake, et al., 1971, JEP; Wade, 1975, Percept. & Psychophys.), dissimilar monocular AIs engaged in rivalry, but to our surprise the AI induced by the suppressed grating subsequently predominated in rivalry following adaptation. Why does a weak AI fare so favorably in rivalry against a stronger AI? This counterintuitive finding may point to the involvement of contrast gain control in binocular rivalry, with contrast signals pooled over orientations and across eyes. This kind of gain control may, in turn, explain why rival targets differing widely in contrast can nonetheless engage in rivalry, with a relatively low contrast contestant occasionally defeating its high contrast opponent.
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