Title

Optical information for the control of steering towards a goal

Date of Completion

January 1999

Keywords

Psychology, Experimental

Degree

Ph.D.

Abstract

Steering towards an object in the environment can be controlled by equalizing the time-to-closure of the heading angle between the object and the direction of locomotion, and the time-to-passage of the observer by the object. Both quantities are optically specified in units of time by the heading angle and the optical expansion of the object, but do not involve perceived object distance. Three experiments required observers to steer through a computer simulated environment towards a target, depicted as a floating cross that did not optically expand, a floating sphere that did optically expand, or a post resting on the ground plane that did optically expand. Because the heading angle was defined in all three conditions, one would expect no differences between target types if steering is based on the heading angle alone. Time-to-passage was specified in the post and sphere conditions, but not in the cross condition. Hence, if steering is based on perceived time-to-passage, then one would expect better performance in the post and sphere conditions than in the cross condition. Target distance was indicated in the post condition by the target's height in the visual field. Hence, if steering is influenced by perceived target distance, then one would expect more reliable performance in the post condition than in the sphere or cross conditions. Experiment 1 revealed that steering was more successful in the post and sphere conditions than in the cross condition. In Experiment 2, steering was unaffected by target size, indicating that steering is not influenced by perceived target distance based on image size. Experiment 3 revealed differences in steering behavior between target types, and confirmed the hypothesis that observers were so moving as to equalize the time-to-closure of the heading angle and the time-to-passage of the target. ^