RELAY: Robotic EyeLink AnalYsis of the EyeLink 1000 using an Artificial Eye

TL;DR

This study used an artificial eye to systematically evaluate the impact of brightness conditions on eye tracking accuracy and pupil measurement, confirming the robustness of the EyeLink 1000 under varying illumination.

Contribution

We developed a controlled artificial eye setup to assess the effects of brightness on eye tracking measurements, providing evidence of the system's accuracy and identifying gaze-dependent pupil size variations.

Findings

EyeLink 1000 shows high accuracy and precision across brightness conditions.

No significant artifact in pupil size or peak velocity due to brightness changes.

Gaze direction influences measured pupil size systematically.

Abstract

There is a widespread assumption that the peak velocities of visually guided saccades in the dark are up to 10~\% slower than those made in the light. Studies that questioned the impact of the surrounding brightness conditions, come to differing conclusions, whether they have an influence or not and if so, in which manner. The problem is of a complex nature as the illumination condition itself may not contribute to different measured peak velocities solely but in combination with the estimation of the pupil size due to its deformation during saccades or different gaze positions. Even the measurement technique of video-based eye tracking itself could play a significant role. To investigate this issue, we constructed a stepper motor driven artificial eye with fixed pupil size to mimic human saccades with predetermined peak velocity \& amplitudes under three different brightness conditions with the EyeLink 1000, one of the most common used eye trackers. The aim was to control the pupil and brightness. With our device, an overall good accuracy and precision of the EyeLink 1000 could be confirmed. Furthermore, we could find that there is no artifact for pupil based eye tracking in relation to changing brightness conditions, neither for the pupil size nor for the peak velocities. What we found, was a systematic, small, yet significant change of the measured pupil sizes as a function of different gaze directions.