Visual and nonvisual contributions to perceived ego-motion studied with a new psychophysical method.

The perception of ego-velocity (PEV) during sinusoidal linear acceleration (otolith stimulation) is investigated with a psychophysical method proposed by Wertheim (1990;1). This method is based on the threshold for object motion perception measured during ego-motion. In a first experiment, PEV was measured both with and without illumination of the experimental room. It was shown that, for the particular frequency and amplitude of ego-motion used, PEV in the light approached physical ego-velocity, whereas in darkness PEV was significantly smaller than physical ego-velocity. In a second experiment the PEV was measured again without illumination of the experimental room. It was found that in response to a sinusoidal ego-velocity stimulus, PEV was sinusoidal as well with a gain of 0.8 and a phase-lead of 4 degrees at 0.15 Hz.