Changzhi Huang^1,2 (), Rong Jiang^1,2, Ming Meng^1,2; ¹Philosophy and Social Science Laboratory of Reading and Development in Children and Adolescents (South China Normal University), Ministry of Education, China, ²School of Psychology, South China Normal University, Guangzhou, 510631, China

The human visual system efficiently processes moving or changing stimuli, as these stimuli are known to attract attention and facilitate breaking suppression to reach perceptual awareness. We investigated how contrast changes—increases and decreases in stimulus intensity—affect breaking interocular suppression during binocular rivalry. In Experiment 1a, participants viewed dichoptic sinusoidal gratings of differing orientations. When participants reported full perception of one grating, the contrast of the suppressed grating increased or decreased over 100 ms. Reaction times for the suppressed stimulus to gain perceptual dominance were recorded. For comparison, static baseline conditions with constant contrasts matching the final intensities of the changing contrast conditions were included to isolate effects of intensity changes from constant intensity differences. Results showed that contrast increases led to significantly faster breakthroughs into perceptual dominance compared to decreases. Increases also resulted in faster breakthrough than the constant higher-intensity condition, indicating a specific facilitative effect of increasing intensity. Conversely, decreases delayed breakthrough than the constant lower-intensity condition, demonstrating an asymmetry in subliminal processing favoring increases. To further validate these findings, Experiment 1b involved faster intensity changes over only 10 ms, and Experiment 1c recorded the time for partial breakthroughs of the changing stimulus. Both results were consistent with Experiment 1a. Experiment 2 presented random dots moving in different random directions dichoptically, making interocular conflict imperceptible and non-reportable. Under these conditions, any change in intensity—regardless of increase or decrease—led to easier breakthrough of interocular suppression. Together, our findings reveal an asymmetric effect of contrast changes during binocular rivalry. When observers are aware of rivalry switches, increases in intensity facilitate perceptual breakthrough while decreases hinder it. When switches are not perceived, any contrast change enhances perceptual breakthrough. These results highlight the interplay between subliminal sensory processing of contrast changes and conscious awareness, shedding lights on developing theoretical models of binocular rivalry.

Acknowledgements: This work is supported by (1) the National Nature Science Foundation of China (Grant No. 31871136), (2) the Science and Technology Ministry of China (Grant No. 2021ZD0204200), and (3) the Sino-German Center for Research Promotion (Grant No. M-0705).