The effects of linear acceleration on the vestibulo-ocular refle

The effects of linear acceleration on the vestibulo-ocular reflex (VOR) were studied in ten cats. Eye movements induced by pulses of angular acceleration were recorded. Angular acceleration stimulated the semicircular canals and during some of the test runs, a centripetal linear acceleration stimulus was also applied to stimulate the otolith organs during the angular acceleration pulse stimulus.;During some test runs the cat's horizontal semicircular canals were stimulated by orienting the cat in the upright position. During other tests the cat's vertical semicircular canals were stimulated by orienting the cat on its side during testing. The direction of gravity was always constant with respect to the plane in which the test was performed.;The slow phase eye velocity data of the resulting nystagmus were fitted to a second-order function that described a damped sinusoid consistent with the torsional pendulum model of the vestibular system. The maximum slow phase eye velocity (MEV) and the time constant (tau) for each run were predicted by fitting the data to the second order function.;Multivariate analysis of variance (MANOVA) for repeated measures design suggested that linear acceleration, under the conditions for this research, did indeed alter the vertical but not the horizontal VOR. It cannot be said that different linear accelerations affected MEV for vertical eye movements, but tau increased linearly as applied linear acceleration increased from the dorsal to ventral surfaces of the cat. A change in linear acceleration of 1 g caused tau to change 5.7 s. For the VOR without linear acceleration stimulus, MEV and tau were greater for upward than for downward eye movements.;Otolith stimulation affected the VOR differently for upward versus downward eye movements. A 1 g change in linear acceleration caused a change in MEV of 63 and 41 deg/s for upward and downward eye movements respectively. It could not be said that tau changed differently for variations in linear acceleration for upward versus downward eye movements.;These findings may prove to be important for understanding the function of the vestibular system as well as for clinical testing of patients with vestibular complaints.