# Do EyelinkDoDriftCorrection and ApplyDriftCorr perform drift correction or drift check with Eyelink 1000?

**URL:** <https://psychtoolbox.discourse.group/t/do-eyelinkdodriftcorrection-and-applydriftcorr-perform-drift-correction-or-drift-check-with-eyelink-1000/5029>\
**Category:** Programming Help\
**Tags:** eyetracking\
**Created:** [June 28, 2023, 3:38pm UTC](https://psychtoolbox.discourse.group/t/do-eyelinkdodriftcorrection-and-applydriftcorr-perform-drift-correction-or-drift-check-with-eyelink-1000/5029 "2023-06-28T15:38:26Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![deblecourt](https://avatars.discourse-cdn.com/v4/letter/d/ec9cab/32.png) [@deblecourt](https://psychtoolbox.discourse.group/u/deblecourt)\
**Post date:** [June 28, 2023, 3:38pm UTC](https://psychtoolbox.discourse.group/t/do-eyelinkdodriftcorrection-and-applydriftcorr-perform-drift-correction-or-drift-check-with-eyelink-1000/5029/1 "2023-06-28T15:38:26Z")

</div>

Hello,

I’m looking into data that I collected using Psychtoolbox version 3.0.15 (maybe 3.0.14) combined with an Eyelink 1000. The data has been collected in MATLAB 2015B.  
I was wondering if the drift correction functions actually perform a drift _correction_ or a drift _check_. In the former case, the values of the calibration map are shifted, but in the latter case, the calibration values are just reported (although the output still reports DRIFTCORRECT, [see this post from SR-Research](https://www.sr-research.com/support/thread-217.html)).  
SR Research notes on their website [[LINK](https://www.sr-research.com/support/thread-213.html)] that for Eyelink 1000 systems

> the default behavior in the Pupil-CR mode in these systems is to simply report the calculated fixation error without altering the calibration map

However, I can’t recover how Psychtoolbox has implemented this.  
My code looks something like this:

```auto
            temp = EyelinkDoDriftCorrect(el);
            Eyelink('ApplyDriftCorr')

```

`el` contains some values about size and colour, as well as the command to display the calibration results and to skip target beeps. The other values are default values coming from `EyelinkInitDefaults`.

So my question is about the behaviour of these commands. Do `EyelinkDoDriftCorrection` and `ApplyDriftCorr` follow the default drift check behaviour as noted by SR-Research, or are they applying an explicit drift correction with a shift of the calibration map?

Thank you in advance for your explanation!

**Edit** : I think I found the answer [in this post](https://www.sr-research.com/support/thread-7483.html?highlight=drift+correction+1000). Unless you send `driftcorrect_cr_disable = off` to the Eyelink or explicitly enable Drift Correction on the host PC, there’s only a drift check without a correction.

---

<div class="post-metadata">

**Author:** ![mariokleiner](https://avatars.discourse-cdn.com/v4/letter/m/13edae/32.png) [@mariokleiner](https://psychtoolbox.discourse.group/u/mariokleiner)\
**Post date:** [June 28, 2023, 5:41pm UTC](https://psychtoolbox.discourse.group/t/do-eyelinkdodriftcorrection-and-applydriftcorr-perform-drift-correction-or-drift-check-with-eyelink-1000/5029/2 "2023-06-28T17:41:26Z")

</div>

These are thin wrappers around the Eyelink C runtime functions `eyelink_apply_driftcorr(), eyelink_driftcorr_start(),` and `do_drift_correct()`. Nothing magic Psychtoolbox specific happens here.

`EyelinkDoDriftCorrect` by default calls Eyelink C runtime function `do_drift_correct()`.  
`Eyelink('ApplyDriftCorr')` calls `eyelink_apply_driftcorr()`.  
If you’d use EyelinkDoDriftCorrect with el.callback set to the non-default value of `[]` ie. empty, then it would call `eyelink_driftcorr_start()` instead.

The function has not changed since 2010, see:

> **[History for...](https://github.com/Psychtoolbox-3/Psychtoolbox-3/commits/beta/Psychtoolbox/PsychHardware/EyelinkToolbox/EyelinkBasic/EyelinkDoDriftCorrect.m)**
>
> Psychophysics Toolbox Version 3 (PTB-3) is a free set of Matlab and GNU Octave functions for vision and neuroscience research. - History for Psychtoolbox/PsychHardware/EyelinkToolbox/EyelinkBasic/E...

Therefore it’s likely that it simply follows/followed Eyelink default behaviour, whatever that is for any given Eyelink model.

-mario