Temporal summation of visual motion.

The sensitivity of the visual system to changes in velocity over time was investigated using the approach that Rashbass [(1970) Journal of Physiology, 210, 165-186] applied to luminance. Pairs of motion impulses (jumps) were presented, and thresholds for discriminating these pairs of impulses from a stationary display were determined. The results were consistent with a model that posits linear filtering of the input velocity, squaring, and integration over some duration. According to the model, the degree of interaction between the impulses reveals the autocorrelation of the impulse response of the motion system. The data were well fit by a three-element cascade of leaky integrators. In the temporal frequency domain, the visual motion system is a lowpass filter. This means that the visual system is quite insensitive to acceleration.