Relating visual and pictorial space: Integration of binocular disparity and motion parallax

Traditionally, perceptual spaces are defined by the medium through which the visual environment is conveyed (e.g., in a physical environment, through a picture, or on a screen). This approach overlooks the distinct contributions of different types of visual information, such as binocular disparity and motion parallax, that transform different visual environments to yield different perceptual spaces. The current study proposes a new approach to describe different perceptual spaces based on different visual information. A geometrical model was developed to delineate the transformations imposed by binocular disparity and motion parallax, including (a) a relief depth scaling along the observer's line of sight and (b) pictorial distortions that rotate the entire perceptual space, as well as the invariant properties after these transformations, including distance, three-dimensional shape, and allocentric direction. The model was fitted to the behavioral results from two experiments, wherein the participants rotated a human figure to point at different targets in virtual reality. The pointer was displayed on a virtual frame that could differentially manipulate the availability of binocular disparity and motion parallax. The model fitted the behavioral results well, and model comparisons validated the relief scaling in the form of depth expansion and the pictorial distortions in the form of an isotropic rotation. Fitted parameters showed that binocular disparity renders distance invariant but also introduces relief depth expansion to three-dimensional objects, whereas motion parallax keeps allocentric direction invariant. We discuss the implications of the mediating effects of binocular disparity and motion parallax when connecting different perceptual spaces.