Detection and discrimination of moving gratings

Two techniques are described which have been used to investigate mechanisms underlying the perception of velocity. The first, subthreshold summation establishes detection thresholds of two gratings of different spatial frequencies moving at the same velocity and also the detection thresholds of combinations of these gratings. The second technique employed a detection/discrimination procedure which establishes the discriminability of two different moving gratings at detection threshold. These experiments suggest that at low velocities the detection of 2 and 6 cycle/degree gratings is mediated by independent mechanisms, this independence being diminished at higher velocities. Gratings of 2 cycles/degree moving at different velocities are only discriminably different at detection threshold when widely separated in velocity.