Percept-switch nucleation in binocular rivalry reveals local adaptation characteristics of early visual processing.

When the two eyes view incompatible images that subtend the entire visual field, perception alternates between the two images unpredictably: at seemingly random times and locations, observers experience sudden changes in the awareness of the unchanging visual stimulation. Here we focus on the very first spontaneous breakout from the very first suppression phase after onset of the two eyes' competing whole-field stimuli. We call such spontaneous local breakout an "initial percept-switch nucleation." We employed homogeneous visual input to examine where, and how, spontaneous local initial percept-switch nucleations originate, demonstrating that their spatial distribution contains locally random inhomogeneities, which are eye- and observer-dependent. We were able to predict the occurrence probability of the percept nucleations by adaptation buildup of the neurons associated with the representation of one eye's image. Intriguingly, the neuronal processes related to both cross-inhibition and local eye dominance could not predict nucleation probability; this is because nucleation inhomogeneity appeared to be different from another previously reported local inhomogeneity known as "onset bias" signifying the local first dominance-choice inhomogeneity upon stimulus onset. Collectively, we reveal a governing role of local adaptation in the neurons associated with early visual processing of one eye's image, in the origination of new phases in awareness.