Adaptation to a linear vection stimulus in a virtual reality environment

Abstract

In the zero-gravity environment of space, the vestibular system's functioning is compromised and astronauts receive conflicting visual and vestibular cues concerning body orientation and motion. Experiment 136 on the Neurolab space shuttle mission explored this research question. The current experiment served as a supporting study, examining human "looming linear vection" responses produced by a virtual checkerboard hallway scene moving towards the observer. In the Earth's gravity environment, the input of the vestibular system can be explored by setting the subject's body orientation (and axis of the vestibular system) in line with or perpendicular to the gravity axis. Five different virtual scene speeds were used. Six vection measures were calculated for each trial: latency, decay latency, peak magnitude of perceived self motion, rise time of magnitude, rise slope, and area (integrated distance traveled). In addition, both latency and magnitude of self-motion were examined for signs of adaptation. Particularly at low scene speeds, the latency of the onset of looming vection was significantly greater in the supine than upright posture, opposite to the effect reported by Kano (1991). Most subjects interpreted the scene as a moving horizontal hallway and the conflict between the visual and gravitational verticals may have delayed the onset of vection in the supine posture. Posture did not affect the magnitude values indicating that the vestibular system plays a minimal role in the perception of speed of self-motion. Virtual scene speed influenced all measures significantly except after-latencies. Latency decreased slightly over the first few trials in the upright posture. However, for both latency and magnitude, adaptation to the stimulus seems to be minimal when considering changes over time in either measure.