Performing a monocular calibration with the Tobii Pro Spectrum

Tobii Pro Spectrum Tobii Pro Eye Tracker Manager Tobii Pro SDK

Learn how to perform a monocular calibration with Tobii Pro Spectrum

The monocular calibration functionality in Tobii Pro Spectrum enables you to collect eye-tracking data that is separately optimized for each of the participant’s eyes. Pro Spectrum identifies the left and right eyes, no matter whether only one or both eyes are visible to the eye-tracking sensors. In some cases, you can increase confidence by covering the untracked eye, but that is not required.

Use this functionality if one troublesome eye causes the binocular calibration process to fail, for example when the participant suffers from severe strabismus, or when he has one prosthetic eye. Separate eye calibration is also useful when researching binocular coordination and fixation disparity, or in situations where you want the calibration to pass even when only one eye is tracked.

Note:

  • A default calibration is used for the eye that was not selected for calibration or failed to calibrate.
  • During the recording, Pro Spectrum still searches for both eyes and will report data for the uncalibrated eye when it can do so.

Types of monocular calibration

Pro Spectrum allows for two types of monocular calibration:
  • Both eyes 
  • Only one eye – left or right
 
Depending on how the calibration flow is implemented in the software, one can choose to perform a calibration for both eyes at a time, calibrate only one eye – left or right, or calibrate one eye and then the other.
 
Calibrate both eyes to compare the calibration performance of each eye or optimize the performance of the eye tracker algorithms during a binocular task.
 
Calibrate only one eye at a time to make sure that only one of your participant´s eyes is calibrated, while ignoring the other eye, if the participant will be performing a monocular task. 
 

Monocular calibration can be performed using either the:

 

Performing a (monocular) calibration with the Eye Tracker Manager

The Tobii Pro Eye Tracker Manager is a software application that helps you set up and manage your connected eye trackers. This application can be used to calibrate your device as well.

  1. Open the Eye Tracker Manager application.
  2. Click the Tobii Pro Spectrum card.
  3. Click Calibrate.
  4. If your setup contains more than two screens, click the icon of the the screen where you will eye track your participant. Click Next.
  5. Click on the Settings drop-down menu to reveal the calibration settings.
  6. Select the calibration mode: Both eyes - to calibrate both eyes independently; Left eye (Monocular) - to calibrate the left eye only; Right eye (Monocular) - to calibrate the right eye only.
  7. Use the position guide window to adjust your position in front of the eye tracker. If your eyes are within range of the eye tracker cameras, you should be able to see two circles in a face contour and the detected gaze data indicator bars should be full. To adjust the distance move your head until the background of the window turns green and the head fits the oval shape (see image above). If you cannot see the two circles and the window is red, try to move around until they appear in the track status window. If this does not work, ask someone else to sit in front of the eye tracker and position them at the right distance. Ultimately, if you are still unsuccessful please restart your computer and run the installation and configuration procedures again.
  8. Click Calibrate to start your calibration procedure.
  9. Evaluate your calibration results. Large systematic errors i.e. a large distance between the average gaze point and the target gaze point may be indicative of a configuration error. No calibration feedback data on the targets located on the top of the screen may indicate that there is a mismatch between the screen size and eye tracker configuration.
  10. Click Recalibrate to improve an unsuccessful calibration (e.g. recalibrating points with missing data for the eye of interest or the error size is insufficient for your research).
  11. Click Use calibration if when you wish to complete your calibration procedure and save it to the eye tracker.

The calibration procedure of the Eye Tracker Manager will always use the monocular calibration feature of Pro Spectrum. In practice this means that each eye will be independently optimized during calibration.

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