Aliasing in the parafovea with incoherent light.

We compared discrimination and detection in the parafovea for oblique, cathode-ray-tube-generated, square-wave gratings. There is a band of frequencies between roughly 10 and 20 cycles/deg wherein such gratings are detected only in an apparently aliased form. The existence of aliasing is consistent with the cone density and optical quality of the parafoveal visual system, but the spatial frequency at which the aliasing is observed is only about half of what is suggested by cone density. The reason for this result is unclear, but one provocative possibility is that the site of the aliasing is neural rather than receptoral.