Temporal dynamics of stereo correspondence bi-stability

Periodic stereoscopic stimuli offer multiple viable solutions to the stereo correspondence problem. When viewing such stimuli for prolonged periods of time, observers continually switch their perceptual state between alternative correspondence solutions. We examine the temporal dynamics of this correspondence bi-stability. Participants were presented with an ambiguous stereogram comprised of regularly spaced dots. This stimulus was perceived as a fronto-parallel plane situated either behind or in front of fixation, depending on the achieved correspondence solution. The stimulus was presented continuously for one minute, with participants instructed to report the sign of the perceived depth at the sound of an auditory prompt presented, on average, every 2 s. Inter-ocular contrast and available disparities were varied so as to manipulate preferred correspondence. We find that participants are initially biased to perceive the stimulus as having an uncrossed disparity. Furthermore, we find that following an initial period of change, perceptual preference and perceptual stability (measured as the probability of an observer's percept changing between consecutive responses) remain constant over the presentation period. Finally, we find that manipulations of matching preference affect both the transient preference for, and stability of, one percept over another. Our results suggest two distinct phases of biasing in the correspondence matching process, one early, the other sustained.