The Tobii eye tracker looks like a regular monitor, or, in the clip version, a compact structure to be attached to any screen or interface. The operating principle is to exceed the limits of a technique in which simple VOG, in which the speed of the calculation is limited by the need for the investigator to analyze images frame-by-frame, instead uses the speed of a computer.
The Benefits
This device allows for recording without contact with the eyes of the subject, and does not necessitate the use of a head-mounted device. The system is able to compensate for fairly large head movements without losing track of the eye.
The tolerance of this technology to physiological differences, such as eye color, use of eyeglasses or contact lenses is higher than any other recording system.
The recording process is fully automated, while quality tracking and accuracy are excellent.
How it Works
The Tobii tracker technology combines the techniques of VOG with infrared reflection: luminescent diodes (NIR-LEDs; Near infra-red light emitting diodes) are integrated in what seems to be just a conventional monitor, which then sends a light beam to the center of the pupil.
Eye movements are then derived from changes in corneal reflex as the direction of this signal changes in relation to the position of the pupil (and thus in relation to the direction of gaze). A video camera with CCD sensors at the base of the monitor can “see” the infrared, it records the reflections: movements are recorded at a rate of 50Hz and with an accuracy of close to 0.5% in the field of vision.
The analysis (carried out by software), allows for the detection of exactly where and for how long the observer directs their attention. The computer generates different types of output that can be studied further. In detail, this information can be: statistically processed as raw data, still images of a particular moment or interaction, or movies in which the observed scenes and the tracks of the eye movement can be superimposed upon each other.
