Getting started with EEGLAB
EEGLAB is an interactive Matlab toolbox for processing continuous and event-related EEG, MEG and other electrophysiological data using independent component analysis (ICA), time/frequency analysis, and other methods including artifact rejection. EEGLAB incorporates and extends the ICA/EEG toolbox of Makeig, and it provides the user with a graphical interface. The homepage of EEGLAB is located at www.sccn.ucsd.edu/eeglab/.
EEGLAB supports external plug-ins and one of them is DIPFIT. With the DIPFIT plugin, you can localize the sources of signal components that have been separated using ICA. The DIPFIT plugin is based on code from Robert Oostenveld, and the same code is included in FieldTrip.
Converting data between EEGLAB and FieldTrip
Both EEGLAB and FieldTrip work with data structures in MATLAB memory. The design philosophy in EEGLAB is to gather all data from one subject in a single “EEG” structure, and all data from a group of subjects in a “STUDY” structure. This is different from the design philosophy of FieldTrip, which does not gather all results in a single structure, but keeps the results from different analyses in different structures.
Together with the EEGLAB developers we maintain two functions for converting the data back and forth: fieldtrip2eeglab and eeglab2fieldtrip. Please note that eeglab2fieldtrip is included in the FieldTrip release, and that fieldtrip2eeglab is included in the EEGLAB release.
Using FieldTrip with the DIPFIT plug-in
The old version 1.x of DIPFIT only fitted dipoles to EEG data using a 4-shell spherical head model. The new version 2.x of DIPFIT also supports realistic BEM volume conduction models for EEG. Currently, EEGLAB cannot support some critical informations about the MEG sensors (the orientations of the gradiometers, mainly) so DIPFIT cannot be use with MEG signal.
To prevent overlapping programming efforts, the DIPFIT version 2.0 plugin uses the forward and inverse methods that are already implemented in FieldTrips dipolefitting function. That means that you can use the DIPFIT graphical interface in EEGLAB, but you should have installed FieldTrip on your Matlab path.
Using other FieldTrip functions
Besides using FieldTrip as the underlying “engine” for the DIPFIT plug-in of EEGLAB, it is also possible to export various aspects of your EEGLAB data structure completely to FieldTrip. Subsequently, you can continue your analysis of the data using the command-line FieldTrip functions
Exporting data from EEGLAB to FieldTrip is done using the eeglab2fieldtrip function. That function takes an “EEG” Matlab structure as input, and will give a Matlab structure as output that is identical to the output format of one of the standard FieldTrip functions (e.g. timelockanalysis or freqanalysis).