Learning the answers to questions such as these would, we hoped, begin to give us clues to Internet news reading behavior that could subsequently be correlated with civic action. They used their own bookmarked sites in normal fashion, scrolling screens as they read, switching from site to site, entering forums if they liked, and so forth. After the bugs were worked out, we proceeded to Chicago and St. Petersburg, Fla., where we collected valid data on 34 and 33 subjects respectively for a total of 67 . Subjects wore a lightweight SMI EyeLink eye tracking system that recorded all eye tracking data in a computer. This is a minimally intrusive, lightweight, head-mounted device.
Small cameras attached to a mounting device illuminate eyes with very low levels of infrared light.
They collect images 60 times per second. In addition to measuring the gaze-location of each eye, the EyeLink measures head position from a small camera attached to the computer's monitor. This camera determines where the subject is looking on the screen even as the head moves slightly. This ability was crucial to the study since subjects read news for long periods of time. Specially written software developed by Stanford permanently captured both eyetracking movements and screen content to a computer for later viewing.