Perception of multi-stable stereograms

To solve the stereo correspondence problem, the visual system must make assumptions about the 3-D structure of objects in the world. However, the nature of these assumptions is unclear. The visual system may impose correspondence constraints based on biases for 3-D shape, disparity sign or disparity magnitude, or all three. Here we present a novel ambiguous stimulus, supporting four distinct percepts, which allows us to examine the contribution of these potential sources of matching bias. The stimulus contains multiple strips of periodic dot patterns, where the length of the period defines the available disparities. Owing to variation in period length between strips, our stimulus may be perceived as a convex or concave wedge, or as a top-near or top-far slanted plane. We biased observers' perception of the stimulus between these four solutions by modulating the luminance of the repeating patterns in each strip. Observers reported their perception in a 4AFC task. We find evidence of matching bias based on shape and disparity sign, together with large individual differences in matching preference. To account for our results, we propose a correlation-based model of disparity computation that includes prior biases for both shape and disparity sign