Abstract

According to standard geometrical optics, monocular visual direction for a defocused image is determined by the chief ray, which locates the center of the resulting blur circle. Recent studies of chromostereopsis have indicated that photoreceptor optics, i.e., the Stiles–Crawford effect (SCE), also affects apparent visual direction of defocused images.^1,2 Because photoreceptor directional sensitivity peaks near the normal pupil center, marginal rays are less effective stimuli. If the pupil is displaced with respect to the SCE peak, the effective image may be shifted with respect to the chief ray by the SCE. Using wave optical analysis of a simple water eye model with an apodized pupil to account for the SCE, we calculated that visual direction of defocused images is significantly shifted when the model views through a displaced aperture. We have experimentally measured the effect of the SCE on apparent visual directions by comparing perceived visual directions of defocused images when subjects view through a displaced aperture under photopic and scotopic conditions. As our model predicted, the visual direction under scotopic conditions (no SCE) was determined by the chief ray, but visual direction at photopic levels was significantly different by an amount predicted by the midpoint of zero-crossings in the defocused retinal image in the apodized model eye.

© 1990 Optical Society of America