6533b7d1fe1ef96bd125c433

RESEARCH PRODUCT

Visually produced locomotion in an autokinetic setup.

subject

description

On individual ttials, 15 subjects stood G m before a minicomputer screen displaying a colon in a completely darkened room Subjects were aware that the light source wzs stationary. They were instructed to fixate the colon and to perform nonlocomotive jogging in place for 2 min. and continuously to report their sensations. Room lights were turned on after 30 sec., and subjects' deviations from their starting places were measured. All subjects had moved toward the light source (M = 4.42 m, SD = .43) although they were convinced that they had not moved. Instead, they had reported either the light source approached them or the light source became larger and/or more intense. On a second trial, subjects were cautioned against involuntary locomotion toward the light. In this case, locomotion toward the light was largely reduced or completely absent (M = 0.28 m, SD = .47). A t test for paired observations indicated that the difference was significant (hr = 29.55; p < .001). In two additional independent control conditions, subjects were to perform nonlocomotive jogging in a completely darkened room with no stimulus (n = 9) or while attending to a 50-dB, 1500-Hz tone (n = 12). In these cases, no appreciable forward locomotion occurred. These observations indicate that visual distance cues in an environment lacking optic flow patterns are misinterpreted depending on subjects' hypotheses concerning changes in the observer-environment relationship. Surprisingly, all subjects exclusively relied on kinaesthetic expectation that they themselves would remain stationary, such that unequivocal visual distance information (expansion of a stationary light source) was incorrecdy attributed to either sensory illusion or directional movement of the light source. One possible explanation of the observed involuntary movement toward the light might be that subjects try to fixate the source by slightly displacing their heads toward the light. This postural change relocares body equilibrium correspondingly, which, in turn, leads to an involuntary compensatory movement forwards to maintain balance. The fact that actual locomotion is not perceived by the subjects can be predicted from a model described by Andersen (1986). which suggests that suppressing ocular reflexes by means of a fixation point would reduce the sensation of self-motion in vection studies.