FAQ: Can I perform an online Drift Correction while actively recording gaze data?

[SR-SUPPORT]

In some circumstances (for example in fMRI settings where recalibration between trials is not an option) an online drift correction may be necessary. There are two options - either correcting drift to the location of a mouse click on the Host PC recording screen, or correcting drift to a specific screen location (such as the screen center). Online Drift Correction is not enabled by default, so in each case some parameters need to be added to FINAL.INI file or sent programatically as commands from your stimullus presentation script (see footnote for how to access the FINAL.INI file).

Please see our How-to video for a step-by-step instruction to enable either Online Drift Correction options.

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• Online Drift Correct to Mouse-Click Position
  
  Add the following lines to FINAL.INI:
  
  
  Code:

  driftcorrect_cr_disable = OFF
normal_click_dcorr = ON
online_dcorr_maxangle = 5.0
  
  
• Online Drift Correct to a Fixed Location
  
  Add the following lines to FINAL.INI (adjusting the position parameter coordinates as required):
  
  
  Code:

  driftcorrect_cr_disable = OFF
online_dcorr_refposn 512,384
online_dcorr_button = ON
online_dcorr_maxangle = 5.0
  
  When using this technique the experimenter should give very clear instructions to the participant in terms of what they need to do when performing the auto drift correction. Please make sure that the participants are really fixating on the target before clicking to accept that fixation. If the participant is not fixating the intended location, performing the online correction will compromise the tracker accuracy instead of improving it.
  

In both approaches, the "online_dcorr_maxangle" parameter can be used to specify the maximum distance in degrees of visual angle that is an acceptable drift correction. The default is 5 degrees, and drift larger than that value will not be corrected.

Please see section 3.11.2 Online Drift Correction of the User Manuals for further details.

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*The FINAL.INI file is in the /ELCL/EXE/ folder in the EyeLink partition on the Host PC. The FINAL.INI file can be edited via the file manager software (EyeLink 1000 Plus and EyeLink Portable Duo) or boot the Host PC to Windows (EyeLink II and EyeLink 1000) and edit the file there (the EyeLink partition shows up as another drive when booted to Windows).