Monocular pattern alternation refers to the changes over time in the apparent contrast of the components of a pattern formed by superimposing two sinusoidal gratings. In Experiment 1, alternation rate was measured as a function of the orientation, spatial frequency, and mean luminance of the pattern. Experiment 2 determined pattern alternation rate as a function of orientation, spatial frequency, and contrast. For both experiments, alternation was greater for patterns whose components were horizontal and vertical than for patterns whose components were obliquely oriented. These differences were more pronounced at intermediate than at high and low spatial frequencies. With decreases in mean luminance, there was a decline in both the rate of alternation and the differences in rate due to orientation. There was no significant effect of contrast upon alternation rate. Experiment 3 determined the effects of viewing time upon pattern alternation. For both horizontal-vertical and oblique patterns, the frequency of alternation increased with time up to 100-200 sec and then leveled off. However, the rate of increase with time was greater for horizontal-vertical patterns. These results were discussed in terms of the antagonistic interaction between channels tuned to spatial frequency and orientation.