Object-Based Control of Eye Movement

Washington University, Saint Louis MO

Investigators

Abstract

The visual environment is so full of information that it is simply impossible to process all of it. Instead, people must select parts of the world to process more fully, and parts of the world to process less fully. Two means are available for this selection. First, it is possible to fixate upon a new location in a scene by moving the eyes. Second, it is possible to select covertly, within a fixation, by movements of visual attention. Recently it has become clear that attentional selection is accomplished not merely by reference to a simple spatial coordinate system that might definelocations in a scene, but also by accounting for the physical or perceived objects that are present. Despite several demonstrations of close links between eye movement and attention systems, relatively little is presently known about the role that objects play in selection that involves saccadic eye movements. That issue is the focus of the present project. Four empirical questions regarding the role of objects in selective eye movements will be addressed in separate clusters of experiments. The questions each examine a key way in which eye movements might be affected by the objects in a scene. In the first cluster, experiments examine the extent to which a plan for an eye movement may benefit eye movements to other parts of the targeted object. The second cluster examines the extent to which a plan to make an eye movement may change if the target for the saccade moves. The third cluster explores the possibility that a newly perceived object or the disappearance of an old one may both facilitate eye movements. In the fourth cluster, experiments examine the extent to which eye movements are planned to a location in an object-centered reference frame. In many experiments the objects to be studied are defined not by physical boundaries, but instead by illusory, subjective contours, or by instructions to the subject. Dependent measures include both the latency and the spatial accuracy of the eye movements in the various situations. Answers to the questions addressed in the experiments will contribute to a better understanding of the nature of the reference frames and mental representations that are used by the brain to plan and produce eye movements. Such an understanding will further elucidate the relation between eye movement and attention systems. Taken together, the results will provide important insights into how it is that people select subsets of the world for further processing.