Human Gaze Stabilization During Natural Activities: Translation, Rotation, Magnification, and Target Distance Effects. Benjamin T. Crane and Joseph L. Demer Departments of Ophthalmology and Neurology, University of California, Los Angeles, USA. 90095-7002.
APStracts 4:0082N, 1997.
ABSTRACT
The stability of images on the retina was determined in response to rotational and translational gaze disturbances in 14 normal human subjects during self- generated pitch and yaw, standing, walking, and running on a treadmill. The effects on image stability of target distance, vision, and spectacle magnification were examined. During locomotion the horizontal and vertical velocity of images on the retina was less than 4/s for a visible target located over 4 m away. Image velocity significantly increased to exceed 4/s during self-generated motion. For all conditions of standing and locomotion, angular vestibulo-ocular reflex (AVOR) gain was less than unity and varied significantly by activity, target distance, and among subjects. There was no significant correlation (p > 0.05) between AVOR gain and image stability during standing and walking despite significant variation in both gain and image stability between subjects. This lack of correlation is likely due to head translation which by definition is not considered in AVOR gain calculations. A significant correlation between AVOR gain and image stability was found during active head rotation and some running conditions. The degree of translation and rotation of the orbit varied significantly with activity and viewing condition in a manner suggesting an active role in gaze stabilization. Translation of the orbit was consistently anti-phase with rotation at predominant frequencies below 4 Hz. When orbital translation was neglected in computing gaze, computed image velocities increased. The compensatory effect of orbital translation explains gaze stabilization despite subunity AVOR gain during natural activities. Orbit translation decreased during close target viewing, while orbit rotation decreased while wearing telescopic spectacles. 

Received 4 February 1997; accepted in final form 10 June 1997.
APS Manuscript Number J0104-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 15 July 1997