Table 2.
The eye-trackers. The 1st Purkinje and the CR (corneal reflection) refer to the same infra-red reflection in the cornea. The 4th Purkinje is a reflection in the back of the human lens. The P-CR method calculates uncalibrated gaze as the difference between the centres of the pupil image and the CR image in each video frame of the eye. We also recorded the EyeLink II in pupil-only mode, a predominant setting when measuring micro-saccades, and will report those data later. Polynomial calibration uses the solution of a higher-order polynomial equation system to map P and CR data to gaze, while 3D modelling of the eye estimates parameters of the shape of the eyeball.
| Eye tracker | Interface | Method | Calibration | Sampling frequency (Hz) |
|---|---|---|---|---|
| DPI Gen5.5 | Head fixed | Analog, 1st and 4th Purkinje | Custom | 1000 |
| SMI HiSpeed 240 | Head fixed | P-CR video, filtered | Polynomial | 240 |
| SMI HiSpeed 1250 | Head fixed | P-CR video, filtered | Polynomial | 500 |
| SMI RED250 | Remote | P-CR video, filtered | Polynomial | 250 |
| SMI RED250mobile | Remote | P-CR video, filtered | Polynomial | 250 |
| SMI ETG 2 | Glasses | P-CR video, filtered | 3D model | 60 |
| SR Research EyeLink II | Head fixed | P-CR video, filtered (standard) | Polynomial | 250 |
| SR Research EyeLink 1000+ | Remote | P-CR video, filtered (standard) | Polynomial | 500 |
| Tobii X2-60 | Remote | P-CR video, unfiltered | Polynomial | 60 |
| Tobii T120 | Remote | P-CR video, unfiltered | Polynomial | 120 |
| Tobii TX 300 | Remote | P-CR video, unfiltered | 3D model | 300 |
| Tobii Spectrum | Remote | P-CR video, unfiltered | 3D model | 600 |