Eye-tracking Course

The aim of the eye-tracking training course is to familiarize participants with the eye-tracking hardware and eye-tracking procedures in the Neurobiopsychology Laboratory of the Institute of Cognitive Science at Osnabrück University. The course consists of three parts: (a) the instructor explains and demonstrates all procedures in a first session, (b) the participants practice under guidance and independently, and (c) the participants demonstrate their learned skills to the instructor. Participants use a sample eye-tracking experiment for the training.

General information
Introduction to the eye-tracking lab
Participants are invited to an initial session lasting approximately one hour. The instructor gives a detailed tour and explanation of the process of a typical eye-tracking experiment. Participants are encouraged to take as many notes as possible. The instructor demonstrates how to set up the eye tracker with the help of a separate subject and explains relevant settings and procedures. Particular attention will be paid to the position of the eye-tracker and cameras and the need for accurate calibration and validation of the data. Further details can be found below.

Independent practice sessions
After the introduction, participants will practice their skills in independent sessions without the instructor. On average, participants will need about 5-6 hours of practice sessions (within 7-10 days) to be able to correctly set up the lab and eye-tracker for an experiment.

Skill demonstration
At the end, participants must mimic the setup of an actual experiment (the training experiment) while the instructor watches. If the instructor is satisfied with the participant's performance, the participant has passed the eye-tracking training course. If the instructor is not completely satisfied, the participant must repeat a few practice sessions and then demonstrate their skills to the instructor again. This process is repeated until the participant successfully completes the course.

Procedures and default settings
Available hardware
Participants in the eye-tracking training course use the same equipment that is used for real experiments in the neurobiopsychology lab. The hardware consists of an EyeLink II (SR Research) eye tracker with a sampling rate of 500 Hz and an accuracy of better than 0.03 degrees of the visual field. The eye-tracking software runs on a computer that is connected to a second display computer via LAN. The monitor of the display computer used in the training varies in size and resolution between 24" (1920x1080 pixels) and 32" (3820x2160 pixels), depending on the requirements of the experiment. However, this aspect has no influence on the training itself.

Preparing the laboratory for a session
The training participant is first instructed to prepare everything in the laboratory to welcome the test person. This includes the preparation of the lab itself, but also secondary aspects such as ensuring that everyone entering the hallway during the experiment is aware of the experiment in progress. To do this, a flashing light is switched on in the corridor to remind people to be quiet.

The eye-tracking computer
The training participant learns how to set up the correct physical properties for a particular experiment. This concerns the physical size of the display monitor, its resolution and the distance from the display monitor to the subject's eyes. These properties are assigned in the "final.ini" file directly on the eye-tracking computer. A brief but clear explanation of the necessity and significance of these properties is given to the training participant.

The display computer
On the display computer, the training participant must ensure that the display resolution matches the resolution assigned in the properties of the eye-tracking software as described above. Later, the use of the software console (terminal) will be briefly explained to access the correct folder on the computer containing the experimental scripts and to run the script correctly. Once the experimental script has been started, the correct subject number and file name must be entered.

The eye tracker
After the pre-setup, the subject is asked to sit in front of the display monitor. The training participant is now instructed on how to correctly position and set up the eye-tracking hardware on the subject's head. The EyeLink II eye tracker contains three cameras (one world camera and two eye cameras). The instructor shows the trainee how to correctly set up the world camera and one eye camera. The instructor explains the criteria for a good camera position and shows typical variations in the camera setting to deal with glasses or other potential problems. The training participant then sets up the second eye camera under the supervision of the instructor. Setting up the eye cameras is not easy and requires some experience and skill. Therefore, the participants have enough time to ask questions and practice to achieve a good setup.

The eye-tracking software
In the eye-tracking software, the correct positioning of the three cameras can be checked again. Next, the correct options must be assigned, including the number and structure of the fixation points in the calibration and validation (see below). The clock interval of these fixation points must also be assigned correctly. Then the correct sampling rate (500 Hz) and tracking mode (Pupil) must be applied.
The calibration procedure then begins. The training participant must fixate fixation points in random order for a certain time (pacing interval). The trainee learns the sequence and structure of the calibration output and how to interpret the result. The calibration is followed by a validation of the previous result. Again, the trainee must fix the following fixation points. Now a drift error is calculated for each point. The trainee learns how to interpret the drift error and how to correctly maintain the cameras, readjust and recalibrate the system to achieve an average drift error of better than 0.03 degrees of the field of view.
The experiment then begins with a simple button press. Before each trial, the subject must fixate a fixation point to make a quick drift correction for each trial. The trainee must manually click a button when he/she notices that the subject is fixating the presented point. The trainee is advised not to accept a fixation too quickly to avoid misses, but also not to wait too long to prevent the subject from becoming nervous. The usual presentation time of the fixation point should be 1-3 seconds, depending on the circumstances. During the actual stimulus presentation within each trial, the trainee learns to read the information on the eye-tracking computer screen, including trial duration, current fixation position, pupil detection and live monitoring of camera settings.

Completion
After the experiment, the eye tracker is removed from the subject's head. The computers must then log off. However, the training participant is advised to wait a few more minutes, as the eye tracker has to copy the raw data files to the display computer, which can take some time depending on the size of the data. The warning lights in the corridor must then be switched off.

Additional information
While setting up the hardware and software, the trainee will also learn how to change display monitors before the experiment, if necessary. This includes resetting the eye-tracking sensors captured by the world camera to filter out head movements. The trainee will also be informed of the financial value of the entire system and advised to work as carefully and focused as possible to avoid damage or incorrect settings to the hardware and software.

Course Scheduling and Registration
There is no set schedule or registration process for the Neurobiopsychology eye-tracking training course. Students who wish to acquire the so-called "eye-tracking license" are asked to send an e-mail to the course instructor Johannes Solzbacher.