THE FUNCTIONAL ROLES OF THE MOTION PERCEPTION SYSTEMS

Abstract

There are several sources of visual information about motion. One is simply the motion on the retina, known as optic flow, caused by motion in the world. Another source of flow-based information is the differences between the optic flow fields of the two eyes, known as interocular velocity differences. Also, there is disparity-based information about motion in the form of the changes in binocular disparity over time that result from motion. This dissertation concerns the results of experimental work to determine the functional differences between the systems that utilize these sources of information. In the context of perception of time-to-contact, flow-based information is used to perceive objects moving at high velocity and disparity-based information is used to perceive objects moving at low velocity. When both are available, these cues are not combined. Instead, humans just rely on the superior form of information, given the object’s velocity. In the context of perception of lateral motion, there are greater latencies when processing disparity-based information than when processing flow-based information. Despite this, disparity-based information alone is sufficient to guide perception of, and coordination with, laterally moving objects with no decrease in performance compared to normal viewing conditions that present all sources of motion information. I also discuss work that showed how important motion information is to the perception of static properties like object shape. Specifically, ths work demonstrated that both flow- and disparity-based information are necessary for perception of metric shape, as is 45° or more of continuous perspective change. In addition, static disparity alone is not enough; dynamic changes in disparity are required. Our data suppor1 the way in which the model of R. Foster et al. (2011) combines this information, although this model needs to be revised because it assumed combination of flow and static disparity, not dynamic changes in disparity. Over the course of this work, I have revisited several well-researched perceptual and perceptuomotor tasks and investigated the roles of flow-and disparity-based motion information in their execution. This work has shed light on both the mechanisms that underlie motion perception and the role of motion perception in other tasks.