Design and validation of a simple eye-tracking system

Abstract

To address the need for portable systems to collect high-quality eye movement data for field studies, this paper shows how one might design, test, and validate the spatiotemporal fidelity of a home-brewed eye-tracking system. To assess spatial and temporal preci-sion, we describe three validation tests that quantify the spatial res-olution and temporal synchronization of data acquisition. First, be-cause measurement of pursuit eye movements requires a visual mo-tion display, we measured the timing of luminance transitions of several candidate LCD monitors so as to ensure sufficient stimulus fidelity. Second, we measured eye position as human observers (n=20) ran a nine-point calibration in a clinical-grade chin rest, de-livering eye-position noise of 0.22 deg (range: 0.09-0.29 deg) and accuracy of 0.97 deg (range: 0.54-1.89 deg). Third, we measured the overall processing delay in the system to be 5.6 ms, accounted for by the response dynamics of our monitor and the duration of one camera frame. The validation methods presented can be used: 1) to ensure that eye-position accuracy and precision are sufficient to support scientific and clinical studies and are not limited by the hardware or software, and 2) the eyetracker, display, and experi-ment-control software are effectively synchronized.