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EYE-EEG plugin

Open source MATLAB tool for simultaneous eye tracking & EEG

NEW: Jan 6, 2014 - EYE-EEG downloadable via EEGLAB's extension manager

What is the EYE-EEG plugin?


EYE-EEG is a plugin (or "extension") for the open-source MATLAB toolbox EEGLAB developed with the goal to facilitate integrated analyses of electrophysiological and oculomotor data [1]. The plugin parses, imports, and synchronizes simultaneously recorded eye tracking data and adds it as extra channels to the EEG.

Saccades and fixations can be imported from the eye tracking raw data or detected with an adaptive velocity-based algorithm [2]. Eye movements are then added as new time-locking events to EEGLAB's event structure, allowing easy saccade- and fixation-related EEG analysis (e.g., fixation-related potentials, FRPs). Alternatively, EEG data can be aligned to stimulus onsets and analyzed according to oculomotor behavior (e.g. pupil size, microsaccades) in a given trial. Saccade-related ICA components can be objectively identified based on their covariance with the electrically independent eye tracker [3].

EYE-EEG adds a top-level menu called Eyetracker to EEGLAB. All functions can be accessed via this menu and are saved in EEGLAB's command history. Alternatively, functions can be called from the command line, providing advanced users with the option to use them in custom scripts. Using EEGLAB's export functions, integrated datasets may also be exported to other free toolboxes like Fieldtrip or Brainstorm.

EYE-EEG was written by Olaf Dimigen & Ulrich Reinacher in Werner Sommer's Biological Psychology lab at Humboldt University Berlin.

Why combine eye tracking & EEG?


Everyday vision is an active process that involves making several saccades per second. In contrast, most EEG data is recorded during prolonged visual fixation. An alternative approach to signal analysis (for an overview see [1]), is to time-lock the EEG not to passive stimulus presentations, but to the on- or offsets of saccadic eye movements in more natural viewing situations (yielding saccade- and fixation-related potentials, SRPs/FRPs). However, recording precise eye movements together with the EEG is also useful for many other purposes. These include controlling fixation, detecting signal distortions from microsaccades (e.g., [4]), improving ocular artifact correction [1, 3], measuring saccadic reaction times, presenting stimuli gaze-contingently [5], simultaneous pupillometry, or improving brain-computer interfaces.

Overview over functions


Preprocessing
Import & synchronize
Reject data based on eye position
Apply functions to selected channels
Detect saccades & fixations
Classify independent components
Eye-movement related potentials

For details, please see the tutorial.

Requirements


Software

Hardware

Currently, the plugin reads text-converted raw data from eye trackers by SR Research (e.g., EyeLink™-series) and Sensomotoric Instruments (e.g., iView X™ and RED™-series). If EEG and eye track are already synchronized (see Tutorial: How to connect eye tracker & EEG), the plugin can also be used to further process data recorded with other eye tracking hardware. There are no known limitations regarding EEG hardware, since EEGLAB imports most EEG formats.

Download & Installation


Disclaimer: The EYE-EEG plugin is currently an Beta release, intended primarily for Beta-testing. Not all functions of future releases are guaranteed to be backwards compatible with this version and function inputs and data formats will likely undergo some changes. Versions following 1.0 will be guaranteed backwards compatibility. Nevertheless, you are welcome to use this version and you may find much of the current functionality useful for your purposes.
Installation is simple

  1. Go to the download page. Download a .zip archive containing a folder with the plugin files and a PDF of the reference paper
  2. Unzip and move the entire folder into EEGLAB’s "plugins" directory. Inside this directory, you should now have a subdirectory called "eye_eeg0.41".
  3. Start EEGLAB. It should automatically recognize and add the plug-in. You should see the following line appear in your MATLAB window:

>> EEGLAB: adding "eye_eeg" plugin version 0.41 (see >> help eegplugin_eye_eeg)

That's it. EEGLAB now has an additional menu called "Eyetracker":

EEGLAB with additional eye tracker menu

Getting started


To get started, read the step-by-step tutorial or try out the plugin with example data.

Citing the EYE-EEG plugin


This is free software distributed under the GNU General Public License. However, we do ask those who use this program or adapt its functions to cite it in their work. Please refer to it as the "EYE-EEG plug-in for EEGLAB" and cite reference [1] below. If you use the saccade detection, please additionally cite reference [2]. If you select independent components based on the variance ratio criterion, make sure to also cite reference [3]. Also, please ensure that EEGLAB is cited properly as described on the EEGLAB website.

Contact


For bug reports, feature requests, and all other feedback please email us. We'd be happy to hear of any papers you have written or insights you have gained using EYE-EEG. We also welcome any collaboration in improving the tools, adding features, or supporting additional eye trackers.

Acknowledgements


Development of this software was supported by German Research Foundation grant to DFG Research Group 868, project A2: The timeline of word recognition and oculomotor control in reading (PIs: Werner Sommer & Reinhold Kliegl). Project publications on fixation-related potentials are found here.

References


  1. Dimigen, O., Sommer, W., Hohlfeld, A., Jacobs, A., & Kliegl, R. (2011). Coregistration of eye movements and EEG in natural reading: Analyses & Review. Journal of Experimenta Psychology: General, 140 (4), 552-572 [plugin reference paperPDF]
  2. Engbert, R., & Mergenthaler, K. (2006). Microsaccades are triggered by low retinal image slip. PNAS, 103 (18), 7192-7197
  3. Plöchl, M., Ossandon, J.P., & König, P. (2012). Combining EEG and eye tracking: identification, characterization, and correction of eye movement artifacts in electroencephalographic data. Frontiers in Human Neuroscience, doi: 10.3389/fnhum.2012.00278
  4. Dimigen, O., Valsecchi, M., Sommer, W., & Kliegl, R. (2009). Human microsaccade-related visual brain responses. J Neurosci, 29, 12321-31
  5. Dimigen, O., Kliegl, R., & Sommer, W. (2012). Trans-saccadic parafoveal preview benefits in fluent reading: a study with fixation-related brain potentials. Neuroimage, 62 (1), 381-393