Calibration error in tobii eye X

[Rasa Bhattarai]

Hello,

I have tobii eye X device. Before i run my unity game I check to see if calibration is done properly or not.

1) However, at the tobii setup options: Display device, it shows an virtual image of placement of tobii and ask to place our device within the points of the image. I adjust the position, click done and calibrate it accordingly. But there seems to be change in the virtual image position of the device whenever I open it. What is the procedure to make this virtual image location fix ? Does it cause any problem for the reading of data ?

2) Also, although the sampling rate of tobii eye X is given as 55 to 60Hz, but in my calculations it is different. For 5 samples that i have taken, in every sample there is different sampling rate. Sometimes it is 30hz, 27hz and 25hz etc. but never above 40Hz. Why is the sampling rate different for my device ? Do i need to do some calibration ?

Thanks

[Grant [Tobii]]

Hi @rasa,

But there seems to be change in the virtual image position of the device whenever I open it. What is the procedure to make this virtual image location fix ? Does it cause any problem for the reading of data ?

This is a not a cause for concern. Each time you load the initial setup program, the virtual image position open’s at it’s default position even if it has been ran before at a different position.

Sometimes it is 30hz, 27hz and 25hz etc. but never above 40Hz. Why is the sampling rate different for my device ? Do i need to do some calibration ?

There is to be expected a variation around the nominal value of ~55Hz however that you mention there is no sampling higher than 40Hz is not normal behaviour. You may have already read the article discussing the variable sample rate of the EyeX @ https://link.springer.com/article/10.3758/s13428-016-0762-9

It would be helpful if you gathered a larger sample size and kindly informed us of your methodology to determine the sample frequency. If possible to test with another user as well and report back. Thanks.

[Rasa Bhattarai]

Hi @grant,

Actually i just used Debug.log method in unity to find out the number of eye gaze data points that was recorded during 1 second. But the maximum I received is 30Hz. I ran the program 10 times but everytime it has the same frequency sampling rate. Has my device not been working correctly ? Other than the sampling rate, the 9-point calibration is good. Do i need to try using other tobii eye X device since you said that 40Hz sampling is not normal behaviour.

Thank you.

[Grant [Tobii]]

Hi @rasa, sorry for the delay as I was trying to determine if the debug.log is necessarily a reliable means of determining the sample rate. I think to be certain, the easiest thing would be if you run the Core SDK samples for Visual Studio on your system.

You can download some common sample for free @ https://github.com/Tobii/CoreSDK/tree/master/samples

and running the ‘streams’ samples, you will be able to easily determine the rate of gaze capture in one second (or preferably over a minute and divide by 60).

Please try it out and let us know how you get on…

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