THE SHAPE OF SELF-MOTION PERCEPTION .1. EQUIVALENCE CLASSIFICATION FOR SUSTAINED MOTIONS

Two completely different motions of a subject relative to the earth ca n induce exactly the same stimuli to the vestibular, somatosensory and visual systems. When this happens, the subject may experience disorie ntation and misperception of self-motion. We have identified large cla sses of motions that are perceptually equivalent, i.e. indistinguishab le by the subject, under three sets of conditions: no vision, with vis ion and earth-fixed visual surround, and with vision during possible m ovement of the visual surround. For each of these sets of conditions, we have developed a classification of all sustained motions according to their perceptual equivalences. The result is a complete list of the possible misperceptions of sustained motion due to equivalence of the forces and other direct stimuli to the sensors under the given condit ions. This research expands the range of possible experiments by inclu ding all components of linear and angular velocity and acceleration. M any of the predictions in this paper can be tested experimentally. In addition, the equivalence classes developed here predict perceptual ph enomena in unusual motion environments that are difficult or impossibl e to investigate in the laboratory.