How do we see the motions of objects around us? The way to go about answering this question is to note the kinds of physical motion that occur in the human environment and then to examine the kinds and variables of optical stimulation that correspondingly occur. The isolation and control of these variables with suitable optical apparatus will make possible an experimental psychophysics of kinetic impressions. The desirability of such a psychophysical approach has been pointed out in an earlier paper (Gibson, 1954b) and the following proposals modify or make explicit a number of suggestions there made.