Self-motion magnitude estimation during linear oscillation: changes with head orientation and following fatigue.
Two types of experiments concerning estimated magnitude of self-motion during exposure to linear oscillation on a parallel swing are described in this paper. Experiment I examined changes in magnitude estimation as a function of variation of the subject's head orientation, and Experiments II a, II b, and II c assessed changes in magnitude estimation performance following exposure to sustained, "intense" linear oscillation (fatigue-inducing stimulation). The subjects' performance was summarized employing Stevens' power law (R = k . Sn, where R is perceived self-motion magnitude, k is a constant, S is amplitude of linear oscillation,  and n is an exponent). The results of Experiment  I indicated that the exponents, n, for the magnitude estimation functions varied with head orientation and were greatest when the head was oriented 135 degrees off the vertical. In Experiments II a-c, the magnitude estimation function exponents were increased following fatigue. Both types of experiments suggest ways in which the vestibular system's contribution to a spatial orientation perceptual system may vary. This variability may be a contributing factor to the development of pilot/astronaut disorientation and may also be implicated in the occurrence of motion sickness.
D000054:Acceleration; D000328:Adult; D000337:Aerospace Medicine; D006257:Head / Q000502:physiology*; D006801:Humans; D005222:Mental Fatigue / Q000503:physiopathology*; D009039:Motion Perception; D009041:Motion Sickness / Q000503:physiopathology; D009949:Orientation / Q000502:physiology*; D011984:Sensory Receptor Cells / Q000502:physiology; D014722:Vestibule, Labyrinth / Q000502:physiology