Interactions between disparity, parallax and perspective: Linking a??Reverspectivesa??, hollow masks and the apparent motion seen in random dot stereograms

摘要

Background:Three different perceptual scenarios create the appearance of a rotating 3-D structure during observer motion: Patrick Hughes' a??Reverspectivea?? artworks; hollow masks; and the disparate region of a random-dot stereogram. Papathomas (Spatial Vision 21, 2007) has offered a a??higher levela?? explanation of the three effects based the a??expecteda?? optic flow while Rogers and Gyani (Perception, 2009, in press) have put forward a low-level explanation based on the properties of the stimulation. One problem in understanding these different effects, and their relationships, has been the difficulty of manipulating the variables involved. For example, the direction and amount of parallax motion is a fixed consequence of the particular 3-D structure used. Purpose: The present experiment was designed to independently manipulate (i) the direction and amount of motion parallax; as well as (ii) the binocular disparities; and (iii) the richness of the perspective information. In doing this, we created a continuum between a??reverspectivesa?? (parallax appropriate for a convex 3-D structure); random dot stereograms (no parallax); and the hollow mask (parallax appropriate for a concave 3-D structure). Methods: A continuous sequence of images was generated depicting a particular 3-D structure seen from a series of different vantage points. The presentation of the sequence was linked to the observer's side-to-side head movements (observer-produced parallax). Results: When either perspective or disparities specified the 3-D structure, the structure appeared to rotate in a direction that was consistent with that information. Perspective information typically dominated over binocular disparities when the two were presented in conflict. Apparent rotation was consistent with a convex interpretation of ambiguous shading information although the effect reversed when disparities were introduced. Conclusions: There is nothing special about the particular scenarios that have been used previously. Rather, they represent particular points on a continuum of possible combinations of 3-D information. Moreover, there is no need to invoke a??higher-levela?? explanations.