Previous studies have demonstrated that human contrast sensitivity curves have marked extremes . This phenomenon has not yet been investigated. The present report describes studies of plots of frequency-contrast characteristics obtained using gratings with orientations of 0°, 90°, and 135°. The results showed that: 1) periodically located extremes were marked on the averaged curve obtained using gratings with an orientation of 0°, while use of gratings with orientations of 90° and 135° gave weak peaks; 2) on repeat testing, the amplitudes of extremes decreased sharply, to the level of disappearance by day 5 of testing. These data lead to the suggestion that the phenomenon of local extremes is not associated with random errors by the subjects but reflects the specific characteristics of information processing by the visual system.