Vertical linear acceleration (otolithic-ocular responses).

Abstract

AbstractA 60‐foot vertical linear acceleration device was used to present linear acceleration forces to test animals within a light sealed capsule. Two types of stimuli were used: !1. constant direction of force with rectilinear alterations of the acceleration rate (0 G and 2 G); and 2. constant direction with curvilinear alterations of the acceleration rates (0 to 2 G). Multiple cycles of alternating G forces were presented during a test run.Cats were used as the experimental animal. Eye movement recordings (vertical and horizontal) were made electronystagmographically. All linear acceleration tests were done in darkness. Analysis of data was done by evaluation of the direct recordings and by algebraic summation of consecutive acceleration cycles.The responses of normal and labyrinth altered cats were similar. Conjugate eye deviation was the most prominent response. Nystagmus rarely occurred. The direction of the conjugate deviation in unilaterally labyrinthectomized – contralaterally semicircular canal plugged preparations (unilateral otolithic animals), was of greatest magnitude when the acceleration force was parallel to the utricular plane from a medial to lateral direction. Reversal of position by 180d̀ generally caused reversal of the direction of conjugate eye deviation.The maximum eye deviation and/or production or alteration of nystagmus was related to the magnitude of jerk or, in other words, the rate of change of acceleration and not to the magnitude of acceleration (rate of change of velocity). The rate of change of acceleration at which these changes occurred was near 1.66G/sec (53 ft/sec3). Correlation with predicted planes from mathematical models is cited.The lack of nystagmus production in this study was contrasted to previous reports of nystagmus production by linear acceleration. It was suggested that nystagmus production by otolithic stimulation may be regularly present when the values of linear acceleration are closer to physiologic levels and/or when the otolithic surface is serially stimulated as when the axis of the resultant force changes direction.The variations in reproducibility of response patterns suggested a limited response range to linear acceleration of the (otolithic) vestibular‐ocular reflex.