Abstract

At the 1985 OSA meeting we demonstrated a dissociation between spatial summation and acuity. The extent of spatial summation varies only about 2X across the parafovea, while acuity varies nearly a log unit. We therefore proposed that in the outer parafovea acuity is primarily determined by the separation between neural detectors, and not by their summation areas. In fact, if the separation between detectors significantly exceeds their summation area, the effects of undersampling (e.g., aliasing) should appear. Since grating orientation is readily lost with undersampling, we used a comparison of simple detection and orientation discrimination to demonstrate aliasing. Although the two measurements are similar in the fovea, they diverge with retinal eccentricity. 7° in the periphery, gratings between 10 and 20 c/deg can be detected only in aliased form. It is significant that this aliasing is certainly not at the level of the photoreceptors, but is proximal thereto, perhaps at the level of spatial summation.

© 1986 Optical Society of America