Re-evaluating Vergence as a Distance Cue

Re-evaluating Vergence as a Distance Cue

Abstract

Vergence is regarded as one of the most reliable sources of egocentric distance information in reaching space. However studies of distance from vergence typically fail to control for (a) initial diplopia in the stimulus and (b) the changing retinal image during convergence. I present the results from two experiments that demonstrate that once these factors are controlled for the gain from vergence drops from 0.86 to 0.16, even when (as in the second experiment) accommodation cues are also present. These results have three important implications. First, they lead us to question whether vergence is used to scale the size and distance of objects. Second, they lead us to question whether vergence is used in conjunction with binocular disparity to scale the depth of the scene. Third, if all our distance cues are either relative (diplopia, relative size) or merely cognitive (familiar size), they lead us to question whether the visual system extracts any information about absolute scale.

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Paul Linton
Centre for Applied Vision Research

Vision scientist working on 3D vision. Author of The Perception and Cognition of Visual Space (Palgrave, 2017).