Adaptation to vertical disparity induced-depth: implications for disparity processing

Abstract

Depth aftereffects produced by prolonged inspection of an object in depth can be mediated by monocular and binocular depth cues. The adapting mechanisms responsible for such effects have not yet been fully determined. Theories of binocular depth aftereffects typically posit a role of an adaptive horizontal disparity sensitive mechanism, implying multiple cue-specific mechanisms for depth aftereffects. Here we examined whether binocular depth aftereffects can be attributed to such a cue-specific mechanism. In Experiment 1 we did so using a technique allowing us to maintain horizontal disparities and vergence constant for our adaptation stimuli, whilst manipulating simulated depth by virtue of a vertical disparity induced-depth effect. We found that depth aftereffects were almost identical to those produced by adaptation to stimuli of equivalent depth produced by conventional horizontal disparity modulations. In Experiment 2, we examined depth aftereffects following adaptation to apparently frontal surfaces produced by different combinations of horizontal and vertical disparity modulations. Aftereffects were close to zero. These results suggest that binocular depth aftereffects are not due to adaptation of a horizontal disparity sensitive mechanism, and we argue that adaptation occurs at the level of a 3D shape sensitive mechanism derived from multiple cues. Experiment 3 was a control to examine whether the two types of adaptation stimuli in Experiment 1 were indeed perceptually the same, since in theory they may differ if vertical disparities influenced metric depth scaling. We found no evidence of this, and concluded that the two classes of stimuli used in Experiment 1, though consisting of very different patterns of disparity, were perceptually equivalent.

Direct extraction of curvature-based metric shape from stereo by view-modulated receptive fields

“…Idealised curvature-based shape coding predicts these pairs of symbols to coincide, whereas the circles only should fall on the origin for a shape code using disparity values or their gradient. Thus, our data favour at least a dominant contribution from curvature-based shape coding, consistent with other results (Domini et al 2001;Duke and Wilcox 2003). Moreover, realistic neural models of curvature-based shape are expected to produce side effects of the same type as the minor deviations from the ideal we observed (Appendix B.3).…”

“…1, one may imagine the required rotation of local tangents to the (μ, ν)-images of the stimuli). Very similar conclusions can be drawn from data obtained by Duke and Wilcox (2003), who used a similar experiment but used shapes with illusory curvatures induced by manipulating the vertical disparity field, so as to correspond to a different viewing distance. Besides confirming the previous conclusions on correction of shape for viewing distance, this experiment shows functional equivalence between various signals (vergence and vertical disparity structure) which normally contain viewing distance information.…”

“…However, the psychophysical data (Domini et al 2001;Duke and Wilcox 2003) exclude this: adaptation is driven not by ν μμ ≈ γ , but by the perceived (possibly illusory) κ. In a two-stage computation, the γ -driven adaptation of the first stage would propagate through the second (κ) stage, which could complicate, but not undo, the effect.…”

“…A highly relevant set of recent shape-adaptation experiments (Domini et al 2001;Duke and Wilcox 2003) indicates that shape extraction from disparity immediately yields object shape. For example, Domini et al 4 Adaptation can avoid many of the complications that arise in interpreting measurements of JNDs or systematic errors (bias) in perceived depth, slant or 'shape': JNDs depend strongly on all the unknown neural noise levels, and biases reflect the unknown errors in viewing geometry estimates that any model which aims to extract object shape must use.…”

“…1.2.3) (Domini et al 2001;Duke and Wilcox 2003) allow either implicit coding by (N ± , A vv )-cell sets or explicit coding by C ± -or C ± -cell pairs. Psychophysical testing is also expected to have trouble distinguishing between the local and bilocal schemes, since these are designed to be functionally equivalent.…”