Velocity perception and discrimination: relation to temporal mechanisms.

Measurements of three aspects of velocity detection are presented: the upper threshold of motion (UTM), perceived velocity and velocity discrimination. UTM (the highest velocity at which a drifting periodic pattern has the appearance of coherent motion) is reduced by adaptation to a similar drifting pattern of low but not medium or high velocity. The range of adaptation velocities over which the perceived velocity of a test pattern is reduced is quite different, the reduction being greatest at medium adaptation velocities. True velocity discrimination for gratings is possible only at low velocities; at higher velocities other cues (such as temporal frequency) are used. These findings are discussed in relation to current models of motion perception.