The problem of disorientation in a moving optical environment was examined. A pilot can experience egocentric disorientation if the entire visual environment moves relative to his body without a clue as to the objectives position of the airplane in respect to the ground. A simple method of measuring disorientation was devised. In this method changes in motor activity were recorded for assessing optically induced disorientation. Subjects were placed into an optokinetic drum which excluded any stationary object from view. Within the nonmoving drum each subject walked straight back and forth with open eyes. In the experimental situation the drum was rotated at various constant speeds. Subjects were requested to walk forward and backward while their walking pattern was traced. (The report includes seven references and eight tables and figures.) (Author/LY)