Abstract: PURPOSE: Binocular rivalry is known as a phenomenon in which observers perceive back-and-forth alterations between two distinct monocular stimuli presented simultaneously. Whether perceptual rivalry could be altered in depression remains less clear. Here we used a binocular rivalry paradigm to investigate whether individuals with subthreshold depression (StD), who have depressive symptoms but fall short of the criteria of major depressive disorder, could have different perceptual rivalry.
METHODS: Both a StD group (N = 31) and a non-depressed group (N = 30) performed two binocular rivalry tasks (non-emotional and emotional). In each 55-s trial of the non-emotional rivalry task, two orthogonally oriented grating stimuli (± 45°) were presented to the left and right eyes respectively. Participants were instructed to report their perception about the orientation of the gratings by continuously pressing corresponding buttons. For the emotional rivalry task, each grating as a foreground was paired with an emotional face (fear, happy, or sad) or a neutral face as a background. Participants were required to only pay attention to the grating in the foreground, and to perform the same test as the non-emotional rivalry task.
RESULTS: For the non-emotional rivalry task, we found no any difference between the StD and the control group. However, for the emotional rivalry task, the dominance duration of gratings paired with sad emotional faces was significantly longer in the StD group than that in the control group.
CONCLUSIONS: Individuals with StD have perceptual bias for sad faces during binocular rivalry, and this bias may be considered as a behavioral biomarker highly associated with StD.

Key words: facial expression, subthreshold depression, binocular rivalry