Abstract
Human sensitivity to the disparity difference between two stimuli depends on the relative orientation of the stimuli (see Farell, VSS 2004). Does perceived depth also depend on relative orientation? To find out, we used a stereo plaid made of two superimposed sinusoids with different disparities. The envelope of the plaid was ring-shaped and surrounded a central comparison-grating patch. One of the plaid's components had zero disparity, the other had non-zero disparity and the central grating matched one of these components in orientation. The observer's task was to judge the depth of the center grating relative to the surrounding plaid.
The perceived depth of the plaid might be expected to depend only on the disparity of the plaid. However, our results showed the importance of the relative orientation of the comparison grating and the components of plaid. When the comparison grating and the plaid's non-zero-disparity component were parallel, the perceived-depth PSE occurred when the comparison grating had a disparity proportional to the component's disparity, with a gain that depended on the horizontal disparity of the plaid as a whole. When the comparison grating and the zero-disparity component were parallel, the gain was lower and independent of disparity of the plaid. We conclude, first, that relative depth from stereopsis varies with the relative orientations of the one-dimensional components of the stimuli, lessening as the orientation difference increases, and, second, that this is the case because relative depth from stereopsis is computed within orientation channels.
Supported by NIH Grant EY 012286