SUBJECT-COINCIDENT COORDINATE SYSTEMS AND SUSTAINED MOTIONS

Vestibular research on human perception of self-motion and orientation generally uses the head-based coordinate system standardized by Hixso n, Niven, and Correia (1966) for specifying accelerations of the subje ct. This paper expands the head-based system to include velocities, th ereby incorporating both the visual and vestibular systems, and formal ly defines the resulting concept of a subject-coincident coordinate sy stem. By capturing the organism's vantage point during self-motion, su bject-coincident systems give a natural framework for studying the rel ationship between stimulus, physiology, and perception; however, the e ssential approach differs from that familiar in traditional physics, s o the necessary equations of motion are developed here. In addition, t hese equations are used to investigate the set of sustained motions, t hose motions that can be sustained over a period of time. These motion s can cause disorientation and misperception of motion because of satu ration or adaptation of the human sensory receptors. The results on su stained motions are summarized in a complete categorization of the set of sustained motions.