A novel psychophysical illusion resulting from interaction between horizontal vestibular and vertical pursuit...

The hypothesis was tested that the perception of an object's motion is made in relation to an internal reference center (IRC), which is under the influence of vestibular receptors. Experiments were designed to evaluate whether induced vestibular self-motion will interact linearly with the perception of a visual target (VT).

The major complaint of vestibular patients is vertigo, an illusion of motion. However, there is as yet no objective method to measure this illusion, which is produced by vestibular stimulation.

Six subjects were instructed to track a vertically moving VT while sinusoidally rotating (0.2 Hz) in the yaw plane at 14, 28, and 42 degrees/s. Eye movements were monitored by electro-oculographic electrodes.

During visual-vestibular interaction, all subjects perceived a VT moving obliquely while the eyes moved in the vertical plane. The subject then tilted the VT trajectory until vertical was perceived. At this time, the eye had an oblique vectorial trajectory. Interactive horizontal eye velocities, both vertical and horizontal components, were compared with those from rotation in the dark, showing a strong positive linear relationship (slope = 0.96, r = 0.84, n = 18).

Results support the hypothesis of an egocentric sense of orientation whereby velocity of external objects is evaluated in relation to an IRC that is dependent on the status of the vestibular system. These methods may lead to new techniques for clinical evaluation of vestibular patients.