A MATLAB tool for simultaneous eye tracking and EEG

Although natural vision involves several eye movements per second, EEG
data is usually recorded during steady fi xation. An alternative approach to
signal analysis, used in several recent studies (for review see Dimigen et al,
2011, JEP:General, 140, 552-72), is to time-lock the EEG to the onsets of saccades or fi xations in unconstrained viewing situations. However, recording
high-resolution eye movements with the EEG is also useful for other purposes: controlling fi xation, detecting signal distortions from microsaccades,
measuring saccadic reaction times, improving ocular artifact correction,
gaze-contingent stimulus presentation (c.f., Dimigen, Kliegl & Sommer,
2012, Neuroimage, 62, 381-93), or coregistration of pupil diameter. To facilitate joint analyses of oculomotor and electrophysiological data, we wrote
a plugin to the popular open source MATLAB toolbox EEGLAB, which
imports and synchronizes eye tracking data and adds it as additional channels to the EEG. Saccades and fi xations are either detected with an extended
version of the velocity-based algorithm by Engbert & Mergenthaler (2006)
or imported from the raw EDF fi le and then added to the existing EEGLAB event structure. Additionally, ocular ICA components can be objectively
rejected based on their covariance with the electrically independent eye
track. Currently, eye trackers from SR Research (EyeLink) and SMI (e.g.,
IView X) are supported. Usage of the plugin is exemplifi ed for an experiment investigating the relative contributions of visual, extraretinal, and
oculomotor signals to fixation-related brain potentials (FRPs) during picture viewing