Mismatch between the screen size in the .yaml file and the one in PsychoPy

Coding
,
1

Hi everyone,

I was wondering what are the consequences of the situation in which the screen size specified in the eye-tracker .yaml file (in mm) doesn’t match the screen size specified in PsychoPy (in pixels). For example, the .yaml file specifies screen size of 530 mm x 300 mm (width x height) which would roughly correspond to 2003 x 1134 pixels, but in PsychoPy the screen size is 1920 x 1080 pixels.

Thank you!

2

Hello,

Correct measurements are required by window units like ‘cm’ and ‘deg’. Having this information mismatch the display will cause stimuli to appear to have the wrong size.

  • mdc
3

An iohub .yaml file can contain information about the diplsay being used for eye tracker calibration, including the screen’s physical dimentions and the distance the subject is sitting from the screen:

        physical_dimensions:
            width: 590
            height: 340
            unit_type: mm
        default_eye_distance:
            surface_center: 500
            unit_type: mm

These are different than the screen resolution that is set for the experiment. They are only used by iohub to 1) record this info to the iohub data file, and 2) calculate pixels per degree (if / when needed). If these values are wrong, it will not impact the accuracy of the gaze data because iohub reports eye tracker position using the coord type specified when you create the psychopy window. You can test this by running the selectTracker Coder demo and see that the displayed gaze position is correct (assuming a good calibration ofcourse).