A TECHNIQUE FOR DETERMINING CONVERGENCE IN HUMAN-SUBJECTS UNDERGOING ROTATIONAL ACCELERATION USING A BINOCULAR EYE-TRACKING SYSTEM

Background: This report describes the measurement of convergent eye mo vements and calculation of the spatial convergence point from the angu lar eye position data. These measurements were made in the dark while the subject experienced inertial motion aboard a centrifuge. This was an exploratory experiment with the goal of evaluating the eyes' conver gence in the dark, and to see if this convergence point is dependent o n inertial motion. Methods: The subject was rotated in the dark on NAM RL's Coriolis Acceleration Platform in Pensacola, FL. The pupil positi ons were tracked by two helmet-mounted infrared cameras connected to a computer-controlled data acquisition system. We used the position dat a to calculate the angles through which the eyes rotated, and then app lied trigonometric principles to construct the line of sight for each eye for any instant: in time. The intersection of these two lines of s ight was the convergence point. Results: With the binocular eye-tracki ng system, we could accurately determine an accelerating subject's con vergence point to within 10%, if the point was less than 1.5 m away fr om the subject. At convergence distances greater than 1.5 m, the angul ar movements of the two eyes became so small that determining a conver gence point was difficult.