Increases versus decreases: Asymmetric effects of contrast changes during binocular rivalry modulated by awareness of perceptual switch.

Abstract

The human visual system prioritizes dynamic stimuli, which attract attention and more readily break suppression to reach perceptual awareness. Here, we investigated whether dynamic changes in contrast-either increasing or decreasing-are equally effective in facilitating the breakthrough of suppressed stimuli during binocular rivalry. In Experiment 1a, we found that contrast increases led to significantly faster breakthroughs into perceptual dominance compared with decreases. Notably, increases accelerated breakthrough relative to the unchanged baseline, whereas decreases delayed it. Experiments 1b and 1c replicated the results of Experiment 1a using, respectively, a briefer contrast change (10 ms instead of 100 ms) and partial breakthrough reports, confirming a robust asymmetry in the processing of suppressed stimuli between increases and decreases. In Experiment 2a, random dots moving in different random directions were presented dichoptically, making interocular conflict imperceptible and unreportable. We found that any change in intensity in such rivalry settings-regardless of increase or decrease-promoted perceptual dominance. By introducing motion stimuli into the Experiment 1 paradigm, Experiment 2b demonstrated that the divergence between Experiments 1 and 2 was not due to low-level stimulus differences. Taken together, our results reveal an asymmetric effect of contrast changes during binocular rivalry. This finding highlights the interplay between subliminal sensory processing of contrast changes and conscious awareness, shedding light on developing theoretical models of binocular rivalry.