2.4. Acquisition of Eye-Tracking Data

The EyeTribe [52] optical eye-tracker was used to register oculographic signal. The EyeTribe calculates a pair of (X, Y) coordinates of the user's gaze point with respect to a screen the user is looking at. The coordinates are expressed in pixels. Accuracy of calculating user's eye gaze coordinates is approximately 1°. Such an accuracy can be obtained after proper calibration of the device. Calibration using 9 measurement points was performed for each participant. The EyeTribe also provides information about the occurrence of eye fixations and measures the pupil diameter of both eyes. The eye-tracking signal was registered with a frequency of 60 Hz.