The majority of current models of binocular rivalry assume that alternations between the two dominance states involve interaction between feedback cross-inhibition and slow self-adaptation, ,. This leads to perceptual alternations between the two images even though both stimuli are constantly present. Apparent discrepancies between contrast and coherence experiments could be fully reconciled with adaptation mutual-inhibition models using a simple input transfer-function.īinocular rivalry is a phenomenon which occurs when our eyes receive stereo-incompatible inputs at the same retinal location. Outside that range, the opposite is true. Thus, we found that L4, like L2, is only valid in a limited range of stimulus strengths.
The initial increase in dominance durations was absent in the contrast experiments, but with coherence manipulations, rivalry could be tested at much lower stimulus strengths. The same held true for the alternation periods. When coherence was augmented in both eyes simultaneously, dominance durations first increased at low coherence, and then decreased for further increases in coherence. This is inconsistent with L2 but supports its revision. Both contrast and coherence manipulations in one eye produced robust changes in both eyes dominance durations of the eye receiving the stronger stimulus increased while those of the other eye decreased, albeit less steeply. To circumvent this problem, and to test if the recent revision of L2 has more general validity, we studied changes in binocular rivalry evoked by manipulating coherence of oppositely-moving random-dot stimuli in the two eyes, and compared them against the effects of stimulus contrast. So far, L1–L4 have been tested mainly by varying the contrast of static stimuli, but since binocular rivalry breaks down at low contrasts, it has been difficult to study L4. This observation challenges the validity of those models, but possibly L4 itself is invalid. It was recently demonstrated that adaptation mutual-inhibition models of binocular rivalry capture L4 only in a limited range of input strengths, predicting an increase rather than a decrease in dominance durations with increasing stimulus strength for weak stimuli. Levelt’s four propositions (L1–L4), which characterize the relation between changes in “stimulus strength” in the two eyes and percept alternations, are considered benchmark for binocular rivalry models.