The depth and selectivity of suppression in binocular rivalry

Binocular rivalry occurs when the two eyes are presented with incompatible stimuli and the perceived image alternates between the two stimuli. The aim of this study was to find out whether the periodic perceptual loss of a mo nocular stimulus during binocular rivalry is mirrored by a comparable loss of contrast sensitivity. We presented brief test stimuli to one eye while i ts conditioning stimulus was dominant or suppressed. The test stimuli were varied widely across four stimulus domains-namely, the relative stimulation of medium- and long-wavelength-sensitive cones, duration, spatial frequenc y, and grating orientation. The result in each case was the same. Suppressi on depended slightly or not at all on the type of test stimulus, and contra st sensitivity during suppression was around 64% of that during dominance. The effect of suppression on sensitivity is therefore very weak, relative t o its effect on the perceived image. Furthermore, suppression was largely i ndependent of the similarity between the conditioning and the test stimuli, indicating that our results are better explained by eye suppression than b y stimulus suppression. A model is presented to account for the small, mono cular sensitivity loss during suppression: It assumes that test detection p recedes conditioning stimulus perception in the visual pathway.