Viewing Geometry and Stereoscopic Vision

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

PI: Banks, Martin The proposed research will investigate the means by which we see 3-dimensionally via binocular vision. The research will focus on two issues: 1) how the human visual system solves the "matching problem" in binocular vision and 2) how the visual system represents surface shape and orientation from binocular depth cues. The matching problem in binocular vision has been actively researched for decades. We still do not fully understand how the problem is solved. The matching problem is simply stated in the following way: For every image point in the left eye, the visual system must find the appropriate point in the other eye to match with it. With N possible points, the number of theoretically possible matches is N4 so with large N the matching process can become computationally unmanageable. The visual system can massively reduce the number of possible matches by using what is termed the epipolar constraint. For an image point in one eye, its match must lie on the corresponding epipolar line in the other eye. By using the epipolar constraint, the matching problem can be reduced to a one-dimensional search. However, when the eyes' positions change (e.g., fixating from far to near), the positions and orientations of corresponding epipolar lines change on the retina. Thus, to implement the epipolar constraint, the visual system must take the eyes' positions into account. We have developed an experimental procedure that will allow us to determine whether the visual system uses the epipolar constraint and, if so, what signals the system uses in order to calculate how epipolar lines ought to move when the eyes move. We will also examine the means by which surface shape is represented in the visual system. An important cue to surface shape is the pattern of horizontal disparities arriving at the two eyes, but those disparities by themselves cannot yield a veridical estimate of shape. Other signals such as vertical disparities or eye-position signals must be used as well. We have shown in the previous grant period that changes in the eyes' vergence can cause a compelling change in perceived shape even when the retinal disparities are completely constant. We also know that prolonged viewing of a curved surface causes a subsequently viewed flat surface to appear curved in the opposite direction. Aftereffects like this have been called "disparity aftereffects" because the explanations offered refer to disparity encoding alone. In the proposed research, we will examine the curvature aftereffect. By manipulating eye-position signals and retinal disparities independently, we can determine whether the aftereffect is caused by adaptation among disparity-encoding mechanisms (which is the prevailing theory) or whether it is caused by adaptation in higher-level, shape-encoding mechanisms. Preliminary measurements suggest that the latter hypothesis is a better predictor of the data. We will also determine how the various signals involved (e.g., eye-muscle signals and vertical disparities) are weighted under different viewing conditions. The proposed work will yield a better understanding of these aspects of binocular vision and, consequently, may yield insights into improvements in visual aids such as binocular microscopes, head- and helmet-mounted displays, and other realistic displays.