ABSTRACT
In the tradition of John Dewey (1896), J. J. Gibson (1966) stated that perceptual systems involve active exploration. A key process in visual exploration ofprimates is fixation (Owens & Reed, 1994), and it is this process that can inform us about an object' s location. The present investigation provides evidence for new oculomotor "information" that supports perception of distance over a range of at least 20 m. By measuring participants' performance during a blind-walking task, we investigated how egocentric distance information is obtained, and used to guide locomotion in the absence of visual and auditory feedback. Rieser, Ashmead, Talor, and Youngquist (1990) showed that participants could view targets up to 21 meters away, and walk to them with their vision occluded. In the present study, participants viewed distant targets through 10 Diopter "base-up" or "base-down" prism glasses prior to walking towards the targets with their vision occluded. These prism glasses caused a vertical shift in participants' gaze inclination. The base-down prism glasses shifted the entire optical field up, while the base-up prism glasses shifted the entire optical field down. As a result, gaze inclination was systematically manipulated under natural conditions which left the structure of the retinal image unchanged. It was OUT hypo thesis that viewing a target through prism glasses would result in anomalous oculomotor information, which would cause systematic errors in distance perception. Participants would walk consistently farther after viewing targets through basedown prism glasses, and shorter after viewing targets through base-up prism glasses.
