The Perception of the Higher Derivatives of Visual Motion.

This report describes theoretical work involved in the early stages of this research effort and gives a brief review of the literature studied during that work. In particular, it reviews work on velocity difference thresholds, since several workers have concluded that judgmental comparisons of velocities at different times accounts for the human ability to discriminate between uniform linear motion in the frontal plane and acceleration. This conclusion is consistent with physiology, where motion detecting units are found to be sensitive to speed in specific directions, and none are known to be turned to respond to particular rates of change of speed. No models of motion perception include provisions for detecting either changes in speed or changes in direction. Direct work on acceleration, however., is flawed. Hence, we devised a novel stimulus composed of sine wave gratings that drift at an average speed across the display. The speed is sinusoidally modulated, thus introducing acceleration and jerk the third dervative. We also control spatial frequency, drift rate and luminance contrast. An experiment is described along with a computer program to permit conduct of the experiment.