Drift Correction vs Drift Check?

TinaAS

Dear All,

We are using the EyeLink 1000 and are trying to implement an experiment using OpenSesame.
Unfortunately, we ran into an issue, using the Pygaze_Drift_Correct Item.
For the item, we enabled „Fixation triggered, no spacebar press required“.

We did try the experiment, using the Eyetracker, to figure out whether it is a Check or a Correction.
For this, we intentionally did not look a the target, and it seemed like the Eyelink performed a drift correction, rather than a drift check.
Additionally, we ran the experiment once with a checked „force drift correction (for EyeLink 1000)“ in the pygaze_init Item and once without. This, however, did not appear to make a difference.

The goal is to perform a drift check, so that the experiment only proceeds if the participant is looking at a drift target. It follows that the experiment will continue quickly if the participant is well calibrated, and if the participant needs recalibration, the experimenter has enough time to initiate that (since the experiment should not continue until the drift target is looked at).

1. Is the “pygaze_drift_correct” Item doing a drift CORRECTION, or a drift CHECK?
   → if it is doing a drift correction, is there an item or function to do a drift check?
2. What function is the “pygaze_drift_correct” item using (e.g. eyetracker.fix_triggered_drift_correction OR eyetracker.drift_correction)?
3. What is the checked/unchecked box - „force drift correction (for EyeLink 1000)“ in the pygaze_init Item doing?

Thank you in advance.
Tina & Nora

sebastiaan

Hi Tina & Nora,

The difference between a drift correction and a drift check is subtle, and I don't believe that you can actually tell the difference between the two by looking at the EyeLink computer. For a drift check, the EyeLink checks whether the difference in (measured) gaze position and some anchor point is small enough. For a drift correction, it does the same thing but also uses this difference to correct the calibration settings.

So the first question is: What makes you think that disabling the "Force drift correction" option doesn't actually disable the drift correction?

Cheers!
Sebastiaan