Tutorial XX: Synchronization with Eyetracker data (event transfer)

Authors: Francois Tadel, Martin Völker

This tutorial introduces how to transfer events from one data set to a second data set of a different type, which was recorded at the same time.

We will explain this on the example of synchronizing ocular data recorded with an EyeLink eye tracker (SR Research, Canada) with a second raw recording, e.g. EEG.

Introduction

Eye tracking is useful to detect blinks, saccades, microsaccades and fixations during an experiment. Typically, the eye tracker software will itself mark the most common artifact typeslike blinks and saccades.

These artifact markers are very useful for the analysis of EEG / MEG data, since specific time periods which are contominated with artifacts can be marked and excluded easily. To do so, we need to synchronize the eye tracker data with our EEG / MEG recordings.

This tutorial focusses on how to snychronize EyeLink data (.edf) within brainstorm with raw data within brainstorm.

Information about the EyeLink can be found at http://www.sr-research.com/index.html.

Requirements

For this function to work, you need specific markers, which are stored within both EEG/MEG and eye tracker data at the same time. The exactly same number of this marker type has to be available in both data sets. They can, however, have different names.

Data import

First of all, the raw recording has to be linked to your brainstorm database, if not already done (?Review continuous recordings).

The EyeLink .edf file can be linked the same as the EEG recordings:

• Switch to the "functional data" view.
  
  

• Right-click on the subject folder > Review raw file

  • Select the file format: "EyeLink eye tracker (*.edf)"

  • Select the .edf file(s)
  • Click "open"
    • Due to the file format, the loading can take a while

Event transfer

Now click on the "Process2" tab.

• Into "Files A", drag and drop the raw data files from which you want to copy the events (in this case, the EyeLink files)

• Into "Files B", drag and drop the recordings into which you want to paste the events; here, the EEG recordings.

It does not matter if the number of files in A and B is different. However, the number of sync markers within each data set has to match.

Now click on

• RUN
• Process selection: Synchronize

  • Transfer events (from A to

Process options

...

Additional documentation

• Forum: Development of eye tracker support http://neuroimage.usc.edu/forums/showthread.php?2193-Is-eye-tracker-data-support-interesting-to-Brainstorm