Contrast gain-control in stereo depth and cyclopean contrast perception

Although human observers can perceive depth from stereograms with considerable contrast difference between the images presented to the two eyes (Legge & Gu, 1989), how contrast gain control functions in stereo depth perception has not been systematically investigated. Recently, we developed a multipathway contrast gain-control model (MCM) for binocular phase and contrast perception (Huang, Zhou, Lu, & Zhou, 2011; Huang, Zhou, Zhou, & Lu, 2010) based on a contrast gain-control model of binocular phase combination (Ding & Sperling, 2006). To extend the MCM to simultaneously account for stereo depth and cyclopean contrast perception, we manipulated the contrasts (ranging from 0.08 to 0.4) of the dynamic random dot stereograms (RDS) presented to the left and right eyes independently and measured both disparity thresholds for depth perception and perceived contrasts of the cyclopean images. We found that both disparity threshold and perceived contrast depended strongly on the signal contrasts in the two eyes, exhibiting characteristic binocular contrast gain-control properties. The results were well accounted for by an extended MCM model, in which each eye exerts gain control on the other eye's signal in proportion to its own signal contrast energy and also gain control over the other eye's gain control; stereo strength is proportional to the product of the signal strengths in the two eyes after contrast gain control, and perceived contrast is computed by combining contrast energy from the two eyes. The new model provided an excellent account of our data (r(2) = 0.945), as well as some challenging results in the literature.