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Duje Tadin, Randolph Blake, Sang Chul Chong; Strength of early visual adaptation depends on visual awareness. Journal of Vision 2006;6(6):698. doi: https://doi.org/10.1167/6.6.698.
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We measured visual adaptation strength under variations in awareness by manipulating phenomenal visibility of adapting stimuli using visual crowding. Results showed that the threshold elevation aftereffect (TEAE) was substantially reduced during crowding, but only if the adapting contrast was low enough to prevent TEAE saturation. This suggests that the previous results reporting the failure of crowding to affect the TEAE (He et al., 1996, Nature) may be explained by TEAE saturation at high adapting contrasts. Importantly, crowding's weakening influence on the build-up of the TEAE was correlated with the crowding strength indexed by performance on the orientation discrimination task. We also examined the effect of crowding on the motion aftereffect (MAE) and found even stronger reduction in the aftereffect strength. These findings indicate that neural events underlying crowding are inaugurated at an early stage of visual processing, since both TEAE and MAE arise, at least in part, from adaptation at the earliest stages of cortical processing. We hypothesize that the absence of visual awareness occasioned by crowding results from a cascade of neural events inaugurated in V1 and culminating in the complete abolishment of neural activity ordinarily associated with visual awareness. This conclusion is supported by the stronger effect of crowding on MAE than TEAE. These findings are analogous to our experiments where we used binocular rivalry to suppress adapting stimuli, including results previously reported at VSS. Taken together, our findings force reinterpretation of previous reports, whose results formed key psychophysical evidence against the direct role of V1 in visual awareness.
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