Physical motions are given to an eye only in the form of optical motions. An optical motion is an event in the optic array, that is, in the light reflected from an illuminated environment to an eye or, rather, to any position in the air where an eye might be placed. The six parameters of optical motion can be visualized as vertical translation of the pattern in the plane, horizontal translation of the pattern, enlargement or reduction of the pattern, horizontal foreshortening of the pattern, vertical foreshortening of the pattern and rotation of the pattern in the plane. An irregular or regular contour shape or an irregular or regular group of spots can be made to undergo continuous perspective transformations, and the observer can note the various types of motion in the plane of the screen. A psychophysical experiment has been performed on the degree of perceived semirotation in depth as a function of the transformation sequence.