Knowledge Base

Running a Test and Calibrating

1. Prepare the Tobii Glasses as described in the preparation section.
2. Brief the participant and ask him/her to sign the consent form.
3. Help the participant to wear the eye tracker glasses.
4. Ask the participant to (1) hold the calibration card at arm's length and (2) look at the center of the circle. Click the Calibrate button in the Tobii Pro Glasses 3 controller application. A message will appear if the calibration is successful.

Recording an Observation in The Observer XT

1. From the Observe menu select Observation and then New. Enter a name for the observation and click OK.
2. Click the Start Observation button. The Observer XT starts the gaze video recording in MediaRecorder and subsequently the acquisition of eye tracker data.
3. At the end of the test, click the Stop Observation button. The gaze video from MediaRecorder with the gaze overlay of the participant is now automatically imported into The Observer XT.

Manual Import of Pupil Diameter Data

Pupil diameter is the distance between the center and the outer edge of the pupil. Pupil size can vary depending on factors such as age and light conditions. The pupil diameter data measured with the Tobii Glasses are not corrected for variations in light. Pupils tend to become bigger (dilate) in low-light situations, allowing more light into the eyes. When there is a lot of bright light, pupils will become smaller (constrict).

Pupil size has been associated with cognitive processes underlying perception, attention, and action for external stimuli. Pupil dilation was shown to indicate interest in the content of presented visual stimuli, revealing sex-specific differences. It is also known to indicate general mental activity and correlate with task difficulty. More recent studies have shown that high-resolution tracking of pupil size can be used to predict perception of specific stimuli and even voluntary decisions about attending to stimuli, suggesting a link between pupil responses and the higher-order brain systems supporting cognition, decision-making, and execution of actions.

References

1. Hess, E. H. & Polt, J. M. Pupil Size as Related to Interest Value of Visual Stimuli. Science 132, 349–350 (1960).
2. Hess, E. H. & Polt, J. M. Pupil Size in Relation to Mental Activity during Simple Problem-Solving. Science 143, 1190–1192 (1964).
3. Kahneman, D. & Beatty, J. Pupil Diameter and Load on Memory. Science 154, 1583–1585 (1966).
4. Einhäuser, W., Stout, J., Koch, C. & Carter, O. Pupil dilation reflects perceptual selection and predicts subsequent stability in perceptual rivalry. Proc. Natl. Acad. Sci. 105, 1704–1709 (2008).
5. Einhäuser, W., Koch, C. & Carter, O. L. Pupil dilation betrays the timing of decisions. Front. Hum. Neurosci. 4, 18 (2010).

Procedure

1. Open the observation in which you want to import the pupil diameter data.
2. Click the Import Data button on the toolbar and select Import External Data.
3. Browse to the folder where MediaRecorder stored the gaze overlay video and the pupil diameter data (by default, C:\Users\Public\Public Documents\Noldus\MediaRecorder\Video Files) and select the appropriate text file.
4. In the Files of Type drop-down list select Tobii Glasses 3 Pupil Diameter (*.txt) and click Open. The data are imported and visualized in the Data and Audio Visualization window.