Cervico-Vestibular and Visuo-Vestibular Interaction

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Abstract
In 8 healthy subjects we studied self-motion perception and nystagmus due to sinusoidal stimulation (amplitude 90° peak to peak, frequency 0.05 Hz) of the horizontal semicircular canals, the cervical propriocep-tors. and the retina. We used an electrically driven rotatory chair and optokinetic drum combination. For cervical stimulation the subject's head was placed in a clamp, attached to the drum. Eye movements were recorded by means of electrooculography. d.c. amplification. Subjects signalled the estimated head position by means of a ‘joystick’. In the present series of experiments the vestibular and cervical informations were played off against each other in combined stimulation conditions with an inter-stimulus phase lag of 0 to 315°. in steps of 45°. Similarly, the vestibular and visual informations were played off against each other. Concerning estimated head position, our main finding is that both the visually and the cervical-ly induced illusion of head rotation overrule the vestibular sensation of head motion. The ocular response to combined vestibular plus cervical stimulation shows that both nystagmus slow phases and saccades of the cervical and the vestibular responses add up by vectorial summation.