Primate Translational Vestibulo-Ocular Reflexes. II. Version And Vergence Responses To Fore-Aft Motion. M. Quinn McHenry and Dora E. Angelaki. Dept. of Otolaryngology, University of Mississippi Medical Center, Jackson MS.
APStracts 6:0529N, 1999.
In order to maintain binocular fixation on near targets during fore-aft translational disturbances largely disjunctive eye movements are elicited whose amplitude and direction should be closely tuned to the horizontal and vertical eccentricities of the target. The eye movements generated during this task have been investigated here, as trained rhesus monkeys fixated isovergence targets at different horizontal and vertical eccentricities during 10 Hz fore-aft oscillations. The elicited eye movements complied with the geometrical requirements for binocular fixation, although not ideally. First, the corresponding vergence angle for which the movement of each eye would be compensatory was consistently less than that dictated by the actual fixation parameters. Second, the eye position with zero sensitivity to translation was not straight ahead, as geometrically required, but rather exhibited a systematic dependence on viewing distance and vergence angle. Third, responses were asymmetric, with sensitivity being larger for abducting and downward compared to adducting and upward gaze directions, respectively. As frequency was varied between 4 and 12 Hz, responses exhibited high pass filter properties with significant differences between abduction and adduction responses. As a result, vergence sensitivity increased as a function of frequency with a steeper slope than that of version. Despite largely undercompensatory version responses, vergence sensitivity was closer to ideal. Moreover, the observed dependence of vergence sensitivity on vergence angle, which was varied between 2.5-10 MA, was largely linear rather than quadratic (as geometrically predicted). We conclude that the spatial tuning of eye velocity sensitivity as a function of gaze and viewing distance follows the general geometrical dependencies required for the maintenance of foveal visual acuity. However, systematic deviations from ideal behavior exist that might reflect asymmetric processing of abduction/adduction responses, perhaps because of different functional dependencies of version and vergence eye movement components during translation.
Received 5 February 1999; accepted in final form 18 October 1999.
APS Manuscript Number J088-9.
Article publication pending Journal of Neurophysiology.
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 21 December 1999