The Stereoscopic Frame of Reference in Asymmetric Convergence of the Eyes

Variation in the orientation and shape of the stereoscopic frame of reference in the horizontal meridian was investigated in response to (a) asymmetric convergence of the eyes and (b) afocal overall and meridional magnifiers. The stimulus patterns were varied from those that offered few clues as to vertical limits to those that contained definite vertically separated contours above and below the fixation target. Readings were taken at three observation distances. The data indicated that the orientation of the individual stereoscopic reference curves approached the objective normal where the stimulus pattern contained distinct vertically separated contours. The results confirmed previous findings that the induced size effect could not alone account for these changes in orientation of the reference curves. Changes in shape of the curves also occurred. The average shape of these curves was characteristic for the individual and it varied with the examination distance in such a way, that, at least qualitatively, suggested a stable shape relationship between subjective and objective visual space.