Differential modification of the equidistance and nonius horopter

Abstract

A conflict between binocular disparity and perspective cues was produced by binocularly observing a trapezoidal window in an illusory orientation. Under these conditions, the perception of depth from binocular disparity in the visual space adjacent to the window is recalibrated by the depth illusion associated with the window. The possible effect of this recalibration upon measures of the horopter was investigated using the criteria of apparent equidistance (the equidistance horopter) and equal subjective directions in the two eyes (the nonius horopter). The equidistance horopter was measured by adjusting a point moveable in depth to the apparent distance of a fixated object. The nonius horopter was measured by vertically aligning two bars, one presented to each eye while gazing at the fixation object. It was found that only the equidistance horopter was modified by the cue conflict involving the trapezoidal window. This differential effect upon the equidistance and nonius horopter was discussed in relation to the concept of corresponding points and the general problem of the recalibration of stereopsis from cue conflicts and percsived egocentric distance.