Abstract
The horopter, is theoretically defined as the location of points in space, from which images are projected onto corresponding points in the two eyes. Typically, the horopter consists of two elements, the horizontal horopter which is an arc intersecting the fixation point and the nodal points of the two eyes in the horizontal plane of regard, and the vertical horopter which a vertical line intersecting the fixation point. Empirically, when participants identify locations in space that stimulate corresponding points, they differ from the theoretical predictions. Furthermore, the empirical horopter differs based on the criterion used to measure it. These include but are not limited to the locus of fused images in space, the locus of zero dichoptic motion, the equal distance criterion, the apparent fronto-parallel plane and the region of maximal stereoacuity. A suggested criterion is also the location of points that do not elicit vergence movements, though no data based on this criterion have been reported. Measuring the horopter using the criterion of zero vergence is the main focus of this study. In two experiments measuring the vergence horopter on the horizontal plane (Exp 1) and the vertical plane (Exp 2), using the nonius alignment procedure, participants indicated whether a texture patch presented at a range of disparities (+/− 3 to 15 min arc) and eccentricities (1–10°) elicited a vergence response as indicated by a change in alignment of two nonius lines.. Results from both experiments support the criterion of zero vergence movements, with a small range of disparities (~5–6 min arc) reliably not eliciting vergence movements, which remains relatively constant across eccentricities.
Acknowledgement: RTP Stipend