Integration of ordinal and metric cues in depth processing

J. Burge, M. A. Peterson, and S. E. Palmer (2005) reported that ordinal, configural cues of familiarity and convexity influence perceived depth even when unambiguous metric information in the form of binocular disparity is available. In their study, a shape that was both convex and familiar (i.e., a face) increased perceived depth in random dot stereograms if the shape was shown in the foreground and decreased perceived depth if it was shown in the background. It is generally assumed that luminance cues are necessary for pre-figural shape representation to influence figure-ground computations in this way (M. A. Peterson & B. S. Gibson, 1993); thus, Burge et al. (2005) had used a luminance edge. In this research, we asked whether configural cues need to be defined by luminance, contrast, or neither. For a sufficiently large disparity pedestal (about 2.5 arcmin), configural cues influenced perceived depth both for second-order contours and for contours defined only by disparity. The integration of ordinal and metric cues seems to be driven by the general saliency of the contours and not only by luminance information. This challenges the notion that the integration of such cues always needs to arise during figure-ground organization through early combinations of luminance-defined shape and binocular disparity.