Effect of signal intensity on perceived speed

The effect of signal intensity (proportion of dots moving in the same direction compared to noise dots that move in random directions) on perceived speed was investigated. It was found that increasing signal level decreased the perceived speed of the stimulus. This finding indicates that global-motion pooling processes play a role in the extraction of speed information. It is suggested that the amount of relative motion in the stimulus influences perceived speed, with perceived speed increasing with increasing relative motion. The results are discussed in relation to the notion that speed and direction are processed, at least in part, differently.