We have a wearable eye-trackers in our lab (SMI ETG-2w), and I hope to start some experiments using it. I notice that many desktop eye-trackers provide a sampling rate at 500-1000 Hz, and allow 9-points calibration before experiment; whereas ours only has a sampling rate at 60 Hz (though it can be upgraded to 120 Hz if we pay some extra money), and only allows 3-points calibration.
We hope to do some serious neuroscience & psychophysics experiments, analyzing saccades, fixations, and pupil size, and the subjects will sit in a lab. No out-doors experiments are currently planned. Now I have some doubt on whether our eye-tracker can provide enough precision & accuracy, as in pilot runs when we show dots on random locations on the screen and let our subjects fixate on it, our eye-tracker could not reliably give the correct fixation locations on some dots.
Does wearable eye-trackers always provide worse data than desktop eye-trackers? I hope someone with some experience on both kinds of eye-trackers can help me know what levels of data quality I can expect at most.
Yes, the desktop eyetrackers have better resolution and data quality. They have higher sampling rate, better calibration procedures, and online correction algorithms for noise and movement related artifacts reduction. If your task doesnt need the subject moving around, the better choice is not a wearable eyetracker.
best regards
Since you already have this wearable eye tracker, I will try to take your worries away a bit.
I wouldn't call your device a bad ET system. Of course, it depends on what you would like to do with it. For example, it is definitely usable for visual world studies, but for reading studies, it is probably not the best choice.
- the specification sheet of the device states that it is possible to set the sampling rate to 120 Hz, in case you have the respective upgrade module. (60 Hz means you make a recording of the eyes' position appr. every 16 ms; whereas 120Hz means you make a recording appr. every 8 ms); in theory, a higher sampling rate would allow you to detect really small differences between participants and/or conditions
- a limitation to a 3 point calibration procedure doesn't necessarily mean that the data accuracy is going to be bad. However, the data quality depends on many different factors, for example make-up on participant's eyes usually screws up the quality. Also, you have to make sure that the tracking glasses sit on the back of the nose correctly. The mean gaze tracking accuracy of your ET is 0.5°, which is not too bad. Also, the software allows you to correct the calibration offline, meaning after data collection.
There are some videos on youtube where you can see how good the quality can be (e.g. https://www.youtube.com/watch?v=3HkGHZb40LU)
- one thing you could try if the accuracy is really too bad is make your stimuli bigger. use the biggest computer screen you can find, or use a video projector to present your stimuli on canvas (or a wall)
All the best,
Johannes
Hey Zhou,
I would add, that it critically depends on what you mean by "serious neuroscience & psychophysics experiments".In the linked question, I have collected some related questions to ET use.
https://www.researchgate.net/post/What_is_the_best_eye_tacking_device_under_1200_dollars
In general, if you don't need subject mobility, more restraints are better (head/chin rest, bite bar, etc.) and will yield better results (in terms of accuracy and precision).
In addition, stationary ETs are currently still faster by a large margin. The fastest VOG-based head-mounted ET is around 300 Hz whereas for stationary, head-fixed VOG-ETs you can got up to 2000 Hz. Since head-mounted ETs use a (low frame rate) scene camera to record the participants environment, many systems don't see the need to go to higher sampling rates.
For fixation analyses, which is more common in psychology & related fields, low sampling rates are not a problem.
But as soon as you go for saccades, sampling rate becomes a critical factor.:
- Small saccades, or even worse: mircosaccades, have very short durations (
Totally depends on your design, remote ETs and Glasses are used for different designs and purposes. Apart from this, glasses have parallax error which made researchers think glasses are low quality.But it is not indeed.
This is in fact surprising how even senior Eye Tracking Researchers, working for many years in the field, are confused between the 2 types of eye tracker technologies, Head Mounted and Remote/Desktop.
See Article Is the eye-movement field confused about fixations and sacca...
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