While most of the work on stereopsis focuses on geometric disparities, humans also respond to intensity (contrast or luminance) disparities in the absence of geometric disparities. A rectangular-wave grating viewed with an intensity disparity engenders two perceptions: a perceived intensity, and a perceived rotation of the individual bars of the grating (the Venetian blind effect). Measuring perceived intensity and perceived rotation in gratings with intensity disparities, we found that the two degrees of freedom from the intensities presented to each eye are conserved in the form of two perceptions: perceived intensity is related to the sum of the grating intensities and perceived rotation is related to the difference. Perceived rotation as a function of intensity disparity was then modeled as a simple difference in the neural response of each eye. Perceived contrast and brightness as a function of intensity disparity were modeled using the two-stage gain-control model.
