Does Changing Vertical Disparity Induce Horizontal Head Movement?

Toru Maekawa,Hirohiko Kaneko

doi:10.1371/journal.pone.0137483

Abstract

Theoretically, one can estimate the direction of an object that is relative to the head using vertical disparity if the distance from the head to the object is known. However, several reports describe vertical disparity as having little or no effect on the perception of visual direction. It has been suggested, however, that the visual processes involved in action are different from those involved in perception, and the effect of visual disparity on action has not been investigated in previous studies. This study investigated the influence of vertical disparity on the stability of head direction as a motor response to visual information. We presented a stimulus consisting of horizontal lines with vertical size-disparity oscillation, and examined whether the stimulus affected the subject’s head movement. The results showed that the head movement in the condition of vertical size-disparity oscillation was not significantly different from that in the condition of no disparity oscillation. Our results suggest that, despite theoretical validity, vertical disparity is not used for controlling head movement.

Highlights

Humans can estimate the direction of objects relative to the head or body in the visual field, which is necessary for perceiving the position of objects relative to them and for performing actions such as grasping or rotating the head toward the object
We examined whether temporal oscillation of the vertical size ratio (VSR) induced the subject’s unconscious head movement
VSR can be a cue for maintaining the head direction relative to a stationary object and the temporal oscillation of VSR can produce head rotation about the vertical axis as explained in the introduction

Summary

Introduction

Humans can estimate the direction of objects relative to the head or body in the visual field, which is necessary for perceiving the position of objects relative to them and for performing actions such as grasping or rotating the head toward the object. It has been suggested that the human visual system uses vertical disparity to estimate the direction of an object that is relative to the head when the distance to the object is known or when the relative positions of the objects are known [5,6,7,8]. This is understandable, intuitively, if one considers the difference in the distances from both eyes to an object at an eccentric location. If an object is PLOS ONE | DOI:10.1371/journal.pone.0137483 September 10, 2015

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