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, though it is less likely to obtain data for the uncalibrated eye. Nevertheless, Pro Spectrum reports data for the uncalibrated eye when it can do so.

There are two types of monocular calibration described in the sections below

Monocular calibration of a single eye

This calibration functionality enables you to calibrate one of the participant’s eyes while ignoring the other.

This type of calibration is available in:

  • Pro Eye Tracker Manager when selecting the Monocular – left or Monocular - right calibration.
  • Pro SDK when using Screen based Monocular calibration class/methods. Read more about it at developer.tobii.com

 

The general Monocular Calibration flow for one eye is: 

  1. Start a Monocular calibration for the eye of interest. Masking the other eye is not necessary, enabling the participant to get a natural viewing experience.
  2. Collect data for a number of points for the eye of interest.
  3. Evaluate the calibration result for the eye of interest:
    • Calibration succeeded: sufficient data has been collected for the eye of interest. Calibration results are presented for the points that have successfully collected data for the eye of interest.
    • Calibration failed: insufficient data has been collected. You should restart the calibration procedure.
  4. Improve a successful calibration by recalibrating points with missing data for the eye of interest or where data is insufficient for your research.
  5. Accept calibration.

 

Using the Eye Tracker Manager:

  1. Open the Eye Tracker Manager application.
  2. On the list of connected eye trackers click on the Tobii Pro Spectrum.
  3. Click on the Calibration disclosure arrow in the Selected Eye Tracker panel, to reveal the first Start Calibration button.
  4. Click Start Calibration.
  5. If your setup contains more than two screens, select the eye tracker screen by clicking on the respective screen in the Available Screens list.
  6. Center the eyes (the two white dots) of the participant in the track box and follow the instructions regarding the distance. Ask the participant to change her/his position or change the position of your eye tracking setup if needed.
  7. Select the calibration mode:
    • Default (Binocular)
    • Monocular - Left eye
    • Monocular - Right eye
  8. Click Start Calibration.
  9. Evaluate your calibration results.
  10. Click Re-calibrate if you wish 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 Accept if when you wish to complete your calibration.

Monocular calibration of any or both eyes

This calibration functionality provides better granularity for your calibration results by telling you whether the participant’s left, right or both eyes have been successfully calibrated for each point. Also, you can complete the calibration even when only one eye has been successfully calibrated. Each calibration performed will replace the previous calibration. This means that one cannot calibrate first the left eye, by performing a Monocular-left calibration, and then the right eye, by performing a Monocular-right calibration, and expect to have calibration for both left and right eyes. In this case, only the right eye will be calibrated at the end.

This type of calibration is only available in the Pro SDK when using Screen based Monocular calibration class/methods.

General Monocular Calibration flow for any or both eyes:

  1. Start a Monocular calibration for any or both eyes.
  2. Collect data for a number of points for both eyes.
  3. Evaluate the calibration result for both eyes:
    • Calibration succeeded: sufficient data has been collected for both eyes, or only for the left or for the right eye. The calibration results indicate the quality of the calibration for any of the points, for any of the eyes.
    • Calibration failed: insufficient data has been collected. You should restart the calibration procedure.
  4. Improve a successful calibration by recalibrating the points with missing data for any of the eye, or where data is insufficient for your research.
  5. Accept calibration.

For more details, read more about it at developer.tobii.com

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