Tracking Strategy in Normal Subjects with Computer Generated Scotoma

Abstract

Visual tracking experiments were conducted on five visually unimpaired subjects. During each of four 1 hour sessions, each subject was asked to track a computer generated target using their eyes only. The stimulus target occupied 0.2° of visual angle and moved horizontally through a range of ± 5°, in periodic sinusoidal and non-periodic patterns. Head stabilization was achieved with a head-rest and bite-bar. Horizontal eye movements were computer sampled at 500 samples/sec from the output of a limbus tracker, and vertical eye movements were sampled from the output of a video based pupil tracker (ISCAN). The first session was used to collect baseline tracking data from each subject. In each of the last three sessions, a software control algorithm allowed horizontal eye position to be utilized as a feedback signal, thus simulating experimenter designed central scotomas. These scotomas had the properties shown in the figure below, and were defined to have horizontal widths of ± 1°, ±2° and ±3° degrees. The vertical eye position data was used in conjunction with know cross-talk characteristics to identify and remove trials in which vertical eye position deviations corrupted the horizontal eye position measure.