Bi-Stability in stereopsis
| R. van Ee (2005). Dynamics of perceptual bi-stability for stereoscopic slant rivalry and a comparison with grating, house-face, and Necker cube rivalry. Vision Research, 45, 29-40. doi:10.1016/j.visres.2004.07.039. |  |
| R. van Ee, L.C.J. van Dam & G.J. Brouwer (2005). Voluntary control and the dynamics of perceptual bi-stability. Vision Research, 45, 41-55. doi:10.1016/j.visres.2004.07.030. | |
| R. van Ee, W.J. Adams & P. Mamassian (2003). Bayesian modeling of cue interaction: bi-stability in stereoscopic slant perception. Journal of the Optical Society of America A, 20, 1398-1406. | |
| R. van Ee, L.C.J. van Dam & C.J. Erkelens (2002). Bi-stability in perceived slant when binocular disparity and monocular perspective specify different slants. Journal of Vision, 2, 597-607. | |
| R. van Ee, G. Krumina, S.P. Pont & S. van der Ven (2005). Voluntarily controlled bi-stable slant perception of real and photographed surfaces. Proceedings of the Royal Society London B, 272, 141-148. | |
In each of these stereograms both perspective and binocular disparity specify surface slant about the vertical axis. You need red/green filters to view them. When the red filter is over the right eye, perspective and disparity specify slants with the same sign and the observer perceives a single stable slanted grid with its right side closer.
However, when the red filter is over the left eye, two stable percepts can be distinguished. In the first percept the grid recedes in depth with its right side closer (it is perceived as a slanted rectangle). In the other percept the left side of the grid is closer (it is perceived as a trapezoid with the near-edge shorter than the far-edge). In fact, the perceived slant depends on the viewing distance; however, when the red filter is over the left eye their signs are always conflicting.
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| Disparity and perspective specified slant = 56 and -70, respectively | Disparity and perspective specified slant = 56 and -50, respectively |
In the fourth stereogram the conflict between disparity and perspective-specified slant is so small that observers generally perceive one slanted plane (no bi-stability)
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| Disparity and perspective specified slant = 56 and -25, respectively | Disparity and perspective specified slant = 56 and 0, respectively |
Most observers with normal stereovision have no difficulty to focus their attending to either of the two 3D percepts. However, during pilot studies and during presentations with audiences at conferences we have asked in the order of 60 observers to report their perceptions while they viewed the ambiguous stimuli and as in many other studies in binocular depth perception we found considerable variability between observers. Some of the observers were able to perceive both the perspective and the disparity-dominated percept (bi-stability), some observers solely perceived the perspective-dominated percept and some solely the disparity-dominated percept. We therefore divided the observers into three classes.
Class 1; Bi-stability observers: Roughly speaking, about 30% of the 60 pilot observers tested were directly able to perceive both the perspective-dominated and the disparity-dominated percept when they were asked to report the percept. The other 70% of the observers initially perceived solely the perspective-dominated percept (even if they knew that bi-stability would be possible). Only after they were told that they were looking at a stimulus that they could see in reversed perspective the majority of them was able to perceive bi-stability.
Class 2; Perspective-dominant observers: About 10% to 20% of the 60 observers kept seeing solely the perspective-dominated percept even after they were coached in trying to perceive the disparity-dominated percept.
Class 3; Disparity-dominant observers: Two observers (very experienced colleagues in stereo vision research) solely perceived the disparity-dominated percept and they were not able to alternate between the disparity- and the perspective-dominated percept.