Determining the visibility of noise in motion signals

A procedure is described for generating stimuli to study the detection of n oise components in motion signals. By using random dots with intensities di stributed according to a Gaussian probability function, a temporally and sp atially continuous mixture of signal and noise components can be realized i n random dot kinematograms. These stimuli were used in a noise detection ta sk, a signal detection task and a direction discrimination task Signal-to-n oise ratio ('coherence') thresholds for the signal detection and direction discrimination tasks were consistent with previous research. Noise can be d etected at levels of approximately 0.5-2.5%, depending on the size of the m otion stimulus. We argue that the noise in the motion stimulus becomes dete ctable when it exceeds the noise intrinsic to the various stages of motion processing. Therefore, the method provides a simple procedure for obtaining measures of equivalent input noise and can be used for estimating internal noise levels of motion processing mechanisms.