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Problem Tobii X3-120 with Pygaze(Opensesame). PupilSizeRight/Left =-1 2times over every 3

I have tried to run an experiment in Opensesame with pygaze. I have a Tobii X3-120.

I notice this problem when I open the output file:

Every 3 measure, PupilSizeRight/Left have value "-1" for 2 times. I attach the image of the top of the data file.  The rest of the file looks the same

Do you have any suggestion?




  • Hi Paolo,

    Usually that indicates missing data. I'll admit that it's a bit weird, considering that the pupil validity is 1, and normal gaze samples seem to be coming through.

    If it keeps happening in good calibrations that produce good gaze samples without a pupil size indication, you might want to check with Tobii directly. (The data is streamed from their tracker and application.)



  • Dear Edwin, thank you for your reply. I tried also on another computer, same results.

    I will try to contact the Tobii support.

    Best regards,


  • Good luck! Please do let us know what the issue was if you find out :)

  • Ehm... : ) I'm sorry for my post, it was my fault! I didn't read the Eye Tracker Specifications properly!

    This was the reply from Tobii Support.

    "Tobii X3-120 model reports pupil size only in bright pupil mode which used only every third sample. Such limitation is mentioned in the user manual of the tracker in Appendix A Tobii Pro X3–120 Eye Tracker Specifications on page 29."

    Then I check the Manual, Appendix A page 35 (on my version), it says:

    "Pupil measurement Yes (40 Hz, bright pupil mode only)

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