No aliasing at edges in normal viewing.

Although spatial aliasing by the extrafoveal retina can occur under natural viewing conditions, it does not commonly disturb our vision. One possible explanation for this is that real scenes do not have sufficient power in the high frequencies to produce aliasing. We examined whether aliasing distorted the appearance of a high contrast edge, which is a common stimulus in the environment. Observers made a two-interval forced-choice discrimination between low-pass filtered and unfiltered edges at 0, 10, 20, and 40 deg eccentricity. This discrimination could be made only when frequency components were removed below both the cone and ganglion cell Nyquist frequencies at each eccentricity. Since supra-Nyquist frequency components could not be detected in edges, they are incapable of producing aliasing.