Different aspects of the role of time as a modulating variable in the processing of visual movement information are analyzed. The efficiency of such a variable in discriminating between processes is stressed. In detection experiments, temporal summation processes are demonstrated that allow us to distinguish between two different Analyzing Systems that process movement information in different ways. These two processes also appear to be effective in modulating the apparent velocity of a grating. The assumption of a Neuro-Sensory Adaptation (NSA) process is then questioned on the basis of the predicted temporal characteristics of the phenomena that it should produce, in particular, the movement aftereffect. From that study, it follows that two classes of visual aftereffects should be assumed. Only one of them is attributable to a NSA process. Further investigation of the movement aftereffect leads to the study of temporal frequency as a factor of temporal summation. Again the results appear to be consistent with the assumption that two different Analyzing Systems are triggered depending upon the Spatial Frequency range of the stirn ulus.