An Architectural model of visual motion understanding

Thesis (Ph. D.)--University of Rochester. Dept. of Computer Science, 1989. Simultaneously published in the Technical Report series.The past few years have seen an explosion of interest in the recovery and use of visual motion information by biological and machine vision systems. In the area of computer vision, a variety of algorithms have been developed for extracting various types of motion information from images. Neuroscientists have made great strides in understanding the flow of motion information from the retina to striate and extrastriate cortex. The psychophysics community has gone a long way toward characterizing the limits and structure of human motion processing. The central claim of this thesis is that many puzzling aspects of motion perception can be understood by assuming a particular architecture for the human motion processing system. The architecture consists of three functional units or subsystems. The first or low-level subsystem computes simple mathematical properties of the visual signal. It is entirely bottom-up, and prone to error when its implicit assumptions are violated. The intermediate-level subsystem combines the low-level system's output with world knowledge, segmentation information and other inputs to construct a representation of the world in terms of primitive forms and their trajectories. It is claimed to be the substrate for long-range apparent motion. The highest level of the motion system assembles intermediate-level form and motion primitives into scenarios that can be used for prediction and for matching against stored models. The architecture described above is the result of joint work with Jerome Feldman and Nigel Goddard [Feldman, 1988]. The description of the low-level system is in accord with the standard view of early motion processing, and the details of the high-level system are being worked out in [Goddard]. The secondary contribution of this thesis is a detailed connectionist model of the intermediate level of the architecture. In order to compute the trajectories of primitive shapes it is necessary to design mechanisms for handling time and Gestalt grouping effects in connectionist networks. Solutions to these problems are developed and used to construct a network that interprets continuous and apparent motion stimuli in a limited domain. Simulation results show that its interpretations are in qualitative agreement with human perception