Abstract
Purpose: The vestibulo-ocular reflex eye movements can be observed psychophysically. When we roll, pitch, or yaw our head, we perceive the movements of texture due to the reflex. The eye torsion reflex by head tilt is of most interest, since it cannot be voluntarily controlled and manifest the clear reflexes.
Methods: Under the “world” conditions, the stimulus was fixed to the environment. Under the “head” conditions, the stimulus was presented by a head mounted display. The images had simple textures such as some horizontal lines depicted with low contrast grays or equiluminant colors. The lines and the background alternated with their colors, flickering at 10–20 Hz. The normal subjects tilted his head as observing the image.
Results: Under the “world” conditions, with the clockwise tilt from left to right lateral in 0.5 second, the subjects first perceived the salient clockwise rotation of the texture then perceived the rather slow counterclockwise rotation that soon died away. When the head was tilted slowly such as in 2 seconds from one lateral to the other, the subjects perceived the consecutive rotations of the texture and observed no counter rotation. The images in the head mounted display gave the opposite directional motion perceptions. The clockwise tilt caused first the counterclockwise and then the clockwise rotations. Though, the motions were rather less salient under the “head” conditions, they were qualitatively similar to that of the “world” except the directions.
Discussions: The motion under the “world” would be derived from the retinal slip of the image caused by the head tilt and the slightly delayed compensating reflex eye torsion followed by the eye returning to the primary orientation. Under the “head” conditions the retinal slips were caused only by the reflex torsions. The slips were in the opposite directions to that of the “world”. These slips were consistent to the observations.