Weird pygaze calibration reports (constant distance value & absurdly high acc values)

ChrIm

Hi,

My pygaze calibrations reports always turn out quite weird. For one thing, the screen distance is ALWAYS 57cm, no matter which eye-tracking device I'm using. I've tried to find out why by inspecting the according files, but to no avail. The other issue is the accuracy, which is always around 700px horizontally and 500px vertically, no matter how well the device was calibrated. In the end, the calibration report doesn't matter all that much in my experiment specifically since I've created a custom validation by which I judge the need for a recalibration. However, I would still like to find out why the results end up like this since it'd be more convenient to report the pygaze calibration results in an article rather than having to explain my custom validation :)

Can you give me a tip where to look for potential culprits? I think the coordinate settings may be to blame, but that's just a hunch.

Thanks in advance!

hanzh

Dear @Edwin

I noticed the same problem as @ChrIm pointed out. For example, this is a calibration report on the Tobii T60:

While I'm pretty sure that I was following the targets closely, the accuracy report seems to show otherwise. It is interesting that those values were so close to the center of the screen. I was wondering if the reports did not show the absolute deviation from the targets but some kind of average position of samples?

Thanks,

Han

GEYUQING

Hi everyone,

I had the same problem using Tobii Spectrum, any advice would be helpful.

Cheers,

Ge

Edwin

Hi all,

Screen distance can only be picked up by systems that can. If yours can't, it will try to fall back on a user-defined value, or (in lieu of that) on the default of 57 cm. To define your screen distance, obviously measure it first , and then add this to your constants.py script:

# Set the screen-eye distance to 60.5 cm
SCREENDIST = 60.5

The same holds true for the screen size, which should be user-defined. For example, if it's 40.3x30.0 cm, include this in your constants.py:

SCREENSIZE = (40.3, 30.0)

High values for "accuracy (in pixesl)" mean that your eye tracker thought you were looking at a different place on the screen than where the central marker was presented. One very common reason for this is that people don't set the correct display resolution. For example, if your display is 1024x768 pixels, but you set 800x600, the tracker will report in the 1024x768 frame whereas your experiment will display in the 800x600 frame. This will lead to mismatches. (The only exception to this when you use a different resolution to your display's, is when you set that different resolution in both the eye tracking software and your experimental software.) To set your resolution correctly, include the following in constants.py (obviously adjusted to your own resolution):

# Set the resolution to 1024x768
DISPSIZE = (1024, 768)

Cheers,

Edwin

PS. VERY IMPORTANT: The values for the speed and acceleration thresholds are ONLY used when event detection is set to "pygaze". Hence, you will not notice any of these values being off if you don't use the "wait_for_*" event functions. Even if you do use them, you'll only be affected by these values being off if you're using the "pygaze" event detection as opposed to "native".

hanzh

Hi @Edwin ,

Thank you for your reply! I have some follow-up questions. I'm now using the PyGaze plug-in in OpenSesame with EyeLink.

1. I assume that DISPSIZE is automatically set as the experiment's resolution and I don't have to set it explicitly?
2. Do any of the PyGaze settings (DISPSIZE, SCREENSIZE, SCREENDIST) override settings in the PHYSICAL.INI in the host PC? I have set them correctly in the .INI file but I'm not sure if they will be changed if I don't set them correctly in opensesame.
3. Finally, if my screen is 1920*1280 but I run experiments in 1024*768, which one should be the correct DISPSIZE?

Thanks a lot for your help!

Han

hanzh

Perhaps @sebastiaan also knows answers to those questions above? :)

Edwin

1. Yes, the resolution you set in OpenSesame is passed as DISPSIZE to PyGaze.
2. Nothing you set through OpenSesame or PyGaze changes the INI file, but they will be used as settings in PyGaze's computations. The INI file is not used for this.
3. You should run your experiment in a 19020x1080 resolution if that is the resolution of your monitor. Alternatively, you could use a monitor with a 1024x768 resolution if you really mean to use 1024x768. (I don't really understand why you wouldn't use the native resolution?)