DEPENDENCE OF SPEED AND DIRECTION PERCEPTION ON CINEMATOGRAM DOT DENSITY

In the present experiments, we find that with abrupt decreases in dot density of random-dot cinematograms, perceived speed decreases, while with abrupt increases in dot density, perceived speed increases. Furth er, in steady-state conditions, perceived speed is also affected in th e same way, but to a lesser degree, by the dot density of cinematogram s. Direction discrimination of random-dot cinematograms is enhanced wh en dot density increases abruptly from one stimulus to the next, but i s degraded when dot density decreases abruptly. Finally, speed discrim ination remains constant even when density changes abruptly. The perce ived-speed and direction-discrimination data are consistent with the M otion Coherence theory which motivated this study, and with models tha t include a smoothing stage similar to this theory. Of the other model s that we consider, most predict that increasing dot density reduces p erceived speed. The speed-discrimination data could not distinguish be tween the different theories.