Misconvergence to the stimulus plane causes apparent displacement of the stimulus elements seen monocularly¹

Abstract

When one binocularly views a group of vertical lines through a ring, the outermost line segments (one on each side) seen within the ring are seen monocularly while the segments of the same lines outside the ring are seen binocularly. The monocular segments appear to be displaced outward with respect to the center of the ring and with respect to the corresponding binocular segments outside the ring. Three experiments examined the extent and direction of this illusory displacement as a function of viewing distance, fixation disparity created by varying the angles of the two arms of a haploscope, and fixation disparity created by a stereoscope and different Nonius stimuli. The results of the experiments confirmed the hypothesis that the apparent displacement is due to misconvergence in accordance with Wells-Hering's laws of visual direction.Key words: apparent displacement, misconvergence, fixation disparity, Wells-Hering's laws of visual direction.It is quite common for objects in the environment to create both binocular and monocular retinal images. Near objects that project binocularly matched retinal images commonly obstruct more distant objects, causing them to project monocular unmatched images to one eye. The visual system processes information about the locations of objects in three-dimensional space from binocularly matched and unmatched retinal images. Many recent studies have examined how monocularly seen objects are seen behind binocularly seen objects 1 The authors wish to thank Linda Lillakas, Alistair P. Mapp, Julio C. Martinez-Trojello, and Mykola Khokhotva for their helpful comments and discussions on several versions of this paper and also thank anonymous reviewers of the first version of the manuscript submitted.