Rod latency can affect perception of motion. We present two gratings in spatial and temporal quadrature. Ordinarily the bright bars of succeeding frames link up to determine the direction of motion.

But when a blue grating alternates with a red one under mesopic conditions, the perceived direction of motion may be unmistakably reversed. This happens near 8Hz, where the temporal phase lag of the rods relative to the cones is close to half a cycle. The red grating is thus perceptually followed by the previous blue grating, with its opposite spatial phase, instead of by the one that actually followed.

Another reversal occurs if a grating made of isoluminant red and blue bars moves to the right a quarter of a cycle after each frame. Under mesopic conditions each frame of red/blue grating is seen first by the cones, and then briefly afterwards by the rods in reversed luminance. At low frequencies, (e.g. 2Hz, 8 frames/sec), the rod delay helps the rod-bright blue bars to couple with the cone-bright red bars of the subsequent frame, creating reversed apparent motion.