VECTION - THE CONTRIBUTIONS OF ABSOLUTE AND RELATIVE VISUAL-MOTION

Inspection of a visual scene rotating about the vertical body axis ind uces a compelling sense of self rotation, or circular vection. Circula r vection is suppressed by stationary objects seen beyond the moving d isplay but not by stationary objects in the foreground. We hypothesise d that stationary objects in the foreground facilitate vection because they introduce a relative-motion signal into what would otherwise be an absolute-motion signal. Vection latency and magnitude were measured with a full-field moving display and with stationary objects of vario us sizes and at various positions in the visual field. The results con firmed the hypothesis. Vection latency was longer when there were no s tationary objects in view than when stationary objects were in view. T he effect of stationary objects was particularly evident at low stimul us velocities. At low velocities a small stationary point significantl y increased vection magnitude in spite of the fact that, at higher sti mulus velocities and with other stationary objects in view, fixation o n a stationary point, if anything, reduced vection. Changing the posit ion of the stationary objects in the field of view did not affect vect ion latencies or magnitudes.