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 homebrewed eye-tracking system. To assess spatial and temporal precision, we describe three validation tests that quantify the spatial resolution and temporal synchronization of data acquisition. First, because measurement of pursuit eye movements requires a visual motion 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, delivering 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 experiment-control software are effectively synchronized.