An indirect measure of perceived distance from oculomotor cues

Abstract

The sensitivity of an indirect method of measuring perceived distance was compared in two experiments with the direct procedure of eliciting verbal reports of distance. Perceived distance was varied by varying the oculomotor cues to object distance. The indirect method, called the "adjustable pivot method," uses an apparatus that physically moves the stimulus object laterally concomitantly with the lateral motion of the head. The magnitude and direction of this concomitant motion determines the distance of the point around which the direction of gaze to the object rotates (the pivot distance) as the head is moved. The pivot distance at which the object appears stationary with head movement measures the apparent distance of the object. Both types of measures were found to vary systematically with the oculomotor distance of the object for points of light (Experiment 1) and extended objects (Experiment 2). A previous study has shown that the adjustable pivot method avoids cognitive errors that can distort verbal reports of distance. The present study, by demonstrating the discriminative capability of this method under conditions in which differences in perceived distance were expected to occur, provides clear evidence that the adjustable pivot method is a sensitive and useful procedure for measuring perceived distance. © 1977 Psychonomic Society, Inc.