STEREOPSIS, VERTICAL DISPARITY AND RELIEF TRANSFORMATIONS

The pattern of retinal binocular disparities acquired by a fixating vi sual system depends on both the depth structure of the scene and the v iewing geometry. This paper treats the problem of interpreting the dis parity pattern in terms of scene structure without relying on estimate s of fixation position from eye movement control and proprioception me chanisms. We propose a sequential decomposition of this interpretation process into disparity correction, which is used to compute three-dim ensional structure up to a relief transformation, and disparity normal ization, which is used to resolve the relief ambiguity to obtain metri c structure. We point out that the disparity normalization stage can o ften be omitted, since relief transformations preserve important prope rties such as depth ordering and coplanarity. Based on this framework we analyse three previously proposed computational models of disparity processing; the Mayhew and Longuet-Higgins model, the deformation mod el and the polar angle disparity model. We show how these models are r elated, and argue that none of them can account satisfactorily for ava ilable psychophysical data. We therefore propose an alternative model, regional disparity correction. Using this model we derive predictions for a number of experiments based on vertical disparity manipulations , and compare them to available experimental data. The paper is conclu ded with a summary and a discussion of the possible architectures and mechanisms underling stereopsis in the human visual system.