Cross-modal slant and curvature matching of stereo- and motion-induced surfaces

Surface orientation, modulation frequency and the detection and perception of depth defined by binocular disparity and motion parallax

Binocular disparity and motion parallax provide information about the spatial structure and layout of the world. Descriptive similarities between the two cues have often been noted which have been taken as evidence of a close relationship between them. Here, we report two experiments which investigate the effect of surface orientation and modulation frequency on (i) a threshold detection task and (ii) a supra-threshold depth-matching task using sinusoidally corrugated surfaces defined by binocular disparity or motion parallax. For low frequency corrugations, an orientation anisotropy was observed in both domains, with sensitivity decreasing as surface orientation was varied from horizontal to vertical. In the depth-matching task, for surfaces defined by binocular disparity the greatest depth was seen for oblique orientations. For surfaces defined by motion parallax, perceived depth was found to increase as surface orientation was varied from horizontal to vertical. In neither case was perceived depth for supra-threshold surfaces related to threshold performance in any simple manner. These results reveal clear differences between the perception of depth from binocular disparity or motion parallax, and between perception at threshold and supra-threshold levels of performance.

The contributions of slant and tilt to the detection of local surface orientation in structure from motion

The contribution of slant and tilt to the detection of differences in local surface orientation was examined for structure-from-motion (SFM) displays of a complex sinusoidal surface. Observers judged whether an elliptical SFM gauge figure appeared to be lying on the surface or intersecting it. The gauge figure orientation either matched the local surface orientation or differed from it in slant, tilt, or both. Similar sensitivity was found for deviations in slant and tilt, but greater biases and variability were found when the gauge figure deviated from the local surface orientation in slant, depending on the sign of the difference between the gauge figure and local surface orientation and the position of the gauge figure. The results are consistent with Stevens' (Biological Cybernetics, 46 (1983) 183-195) discussion of the computational advantages of slant and tilt contributing independently to the detection of differences in local surface orientation. The effects of changes in perceived surface slant and tilt during rotation and of the misperception of surface depth on the detection of local orientation in dynamic images are discussed.

Determinants of object recognition

We demonstrate that performance on an object recognition task can be explained in terms of observer-specific perceptual profiles. These profiles are derived from a battery of tests, including the effects of stereo, texture, outline (occluding contour), and motion cues on amplitude judgements of curved surfaces. Using a task in which observers learned to recognise 'amoeboid' objects, a multivariate regression analysis revealed that three psychometric variables derived from the test battery account for 74% of the variance in learning rate. These variables are choice reaction time, and the relative dependence of amplitude judgements on motion and outline cues. The implications of these findings for the existence of observer-specific perceptual profiles, and their relation to the fundamental psychophysical competences associated with object recognition are discussed.