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Abstract

Many theories of human stereovision are based on feature matching and the related correspondence problem. In this paper, we present
psychophysical experiments indicating that localized image features such as Laplacian zerocrossings, intensity extrema, or centroids are not necessary for
binocular depth perception. Smooth one-dimensional intensity profiles were combined into stereograms with mirror-symmetric half-images such that
these localized image features were either absent or did not carry stereo information. In a discrimination task, subjects were asked to distinguish between
stereograms differing only by an exchange of these half-images (ortho- vs. pseudoscopic stereograms). In a depth ordering task, subjects had to judge
which of the two versions appeared in front. Subjects are able to solve both tasks even in the absence of the mentioned image features. The performance is
compared to various possible stereo mechanisms. We conclude that localized image features and the correspondences between them are not necessary to
perceive stereoscopic depth. One mechanism accounting for our data is correlation or mean square difference.