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Bhavin R. Sheth, Daw-An Wu; Adapting to perceived color. Journal of Vision 2004;4(8):331. doi: 10.1167/4.8.331.
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Viewing a stimulus for some time does not always cause a negative aftereffect (AE), as evidenced by our novel finding of the “anti-McCollough effect” (antiMc; SFN,2002), an AE opposite to the classical color-contingent orientation McCollough AE (Mc). Observers (6 Os) binocularly viewed two static full-field inducers—red and black (rb) horizontal (h) stripes, and black and white (bw) h stripes—alternating in a 10s–10s cycle for 20 min total. 10–30 min later, test h stripes appeared redder, and test vertical (v) stripes greener, than before (p<0.02). V inducers yielded analogous results (3 Os, p<0.05). The antiMc remains unchanged for at least 24 hrs. Here, we investigate what underlies the dramatic inversion in perceived AE. Our use of an achromatic inducer instead of a blank field (Dodwell & Humphrey,1990) is key. During induction, the wb stripes appear mildly green because of the weakly saturated (ws) AE cast by the saturated rb stripes. We propose that the greenish AE causes an after-aftereffect, namely the antiMc. At issue is how the AE of a ws color pattern perceptually dominates that of a saturated one. One way is if its neural representation is higher than that of the saturated color AE. We have evidence for this. It is known that the Mc does not transfer inter-ocularly (Coltheart,1973). We confirmed this (11% transfer, p=0.49). In contrast, the antiMc showed complete inter-ocular transfer (106% transfer, p<0.01). There is inter-hemispheric transfer as well. Adaptation to external stimuli is known to alter perception. In contrast, our work shows that the brain adapts to its internal milieu as well—specifically to what it perceives. In the process of adapting to what is perceived, perception changes yet again. Our work suggests that there is a reverse top-down hierarchy to conscious perception. Representations in lower-order areas can reach conscious perception if competing representations in higher-order areas are not present to suppress it.
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