Binocular sensitivity to the movement or flicker visible in a phase-reversing grating pattern is higher by a factor of about 1.7 to 2.0 compared with monocular sensitivity, at low rates of phase reversal. This factor decreases as the temporal frequency of the phase reversal increases, especially above 10 Hz. For different observers, the ratio may be higher or lower overall with gratings of spatial frequency 5 cycles deg-1 than with 0.5 cycle deg-1 gratings.