Sensation of rotation about a vertical axis with a fixed visual field in different illuminations and in the dark.

This paper compares the motion sensations of a subject rotated about a vertical axis for two fixed visual fields (a large peripheral field and a single central spot) and in darkness. Motion sensation is described in terms of threshold, frequency response, and subjective displacement and velocity. The perception of angular acceleration showed significantly lower threshold and reduced latency time for the illuminated presentation. The level of illumination, however, produced no significant difference in threshold. The subjective frequency response, measured by a nulling method, showed a higher gain in the illuminated presentation, particularly at low frequencies and accelerations. With the subject rotating a pointer to maintain a fixed heading during triangular velocity stimuli, subjective displacements showed no difference for all different visual cues. Magnitude estimates of the after-rotation associated with deceleration from a constant velocity showed a quicker rising speed, larger subjective velocity and longer duration in the illuminated presentation. All the results suggest that the oculogyral illusion is principally responsible for producing a lower threshold in the illuminated presentation, although the fixed peripheral visual field tends to reduce reliance upon vestibular signals. At lower intensity rotation stimuli, this effect is especially apparent.