The superiority of binocular vision over monocular vision has been compared for the detection of stationary sinusoidal grating patterns, and for the detection of the apparent movement induced by rapidly phase-reversing such gratings. The thresholds for binocular and monocular pattern perception were in the ratio 1:2 1/2, as found by previous workers. For apparent movement, however, binocular thresholds were lower than monocular thresholds by a factor of 1.9; for every subject tested (n = 20) the ratio for movement detection was larger than the ratio for pattern detection. The effects of combining inputs from the two eyes cannot be explained solely by linear summation models, but may in some circumstances depend on the nonlinearities of certain types of nerve cell.