Perception of rotation in depth

Abstract

There are a variety of ways in which motion in the environment can provide information about three-dimensional relationships. One transformation that has received increasing attention in both the visual perception literature and in the machine vision literature is rotation in depth. This transformation, which includes any rigid rotation other than a rotation about the line of sight, can provide both a strong impression of depth and specific information about three-dimensional relationships in a rotating object or pattern. Computational theories have been developed concerning the relationships that an observer can potentially extract from the information available in this transformation. If computational theories are to be compared to human performance, a systematic body of data on human perception of rotation in depth is required. Such a body of data has been developing, especially in the last few years. Most of these studies have used computer animation techniques introduced into this area of research by Green. It is now possible to derive some preliminary conclusions from these data about what information is actually used by observers, what sources of information are dominant when multiple sources are available, and what errors occur in perception that can provide insights into the processes that observers apply to this information.The objective of this paper is to bring together these empirical findings concerning the ability of human observers to perceive three-dimensional relationships on the basis of rotation in depth. It is intended to systematize and clarify the current state of knowledge in this area. The following sections are organized about a series of conclusions, ranging from general to specific, concerning three major issues in the perception of objects undergoing rotation in depth. The first is the relationship between perceived depth and perceived relative distance in a rotating object. Perceived depth refers to the three-dimensional structure of an object, without regard to the position of the observer (e.g., the perception of a sphere as a sphere rather than as a circle). Perceived relative distance (or depth order) refers to the perception of which parts of an object are closer and which are more distant (e.g., which is the near hemisphere in a transparent sphere). Perceived relative distance in rotating objects is usually measured with direction of rotation judgments. The remaining two issues concern the variables which determine perceived depth and those which determine judgments of relative distance.