[FieldTrip] Time domain beamformer

Tyler Grummett tyler.grummett at flinders.edu.au
Thu Mar 27 11:51:48 CET 2014

Hello fieldtrip,

I just want to discuss my processing steps and to determine if I have made any analysis errors.

Firstly, I have data converted from eeglab using the following code:

            % convert to fieldtrip
            process = 'componentanalysis';
            data = eeglab2fieldtrip( EEG, process, 'none');

The data is 30 seconds of someone having their eyes closed. There are no trigger codes unfortunately.
I then run the ft_timelockanalysis function (to be used in tf_sourceanalysis), without any configuration settings specified (I will use the defaults).

            % calculating the cross spectral density matrix
            ​cfg = [];
            timelock = ft_timelockanalysis(cfg, data);

The code runs fine without any errors. As it calculates the data to be one trial long, has the code done anything to do the data. What has it timelocked to?

I then calculate the mri_headmodel:

            % the forward model and lead field matrix
            mri = ft_read_mri( 'Subject01.mri');
            cfg = [];
            cfg.write      = 'no';
            cfg.coordsys   = 'ctf';
            segmentedmri = ft_volumesegment(cfg, mri);

            cfg = [];
            cfg.method = 'concentricspheres';
            vol = ft_prepare_headmodel(cfg, segmentedmri);

I then run the source analysis code:

            % Source Analysis: without contrasting condition
            cfg              = [];
            cfg.method       = 'lcmv';
            %                 cfg.grid         = grid;
            cfg.vol          = vol;
            cfg.dics.projectnoise = 'yes';
            cfg.dics.lambda       = 0;
            sourcePost = ft_sourceanalysis( cfg, timelock);

The code also runs fine. However, what I have found is that I cant plot the data using ft_sourceplot.
As I am not 100% on how these functions operate and how to properly run a beamformer on continuous data, I am not sure whether
the step that I have taken are appropriate, or that I am kind of making it up as I go along.

I cant find anywhere how to do a beamformer on continuous data without trials of some sort.

Any help will be appreciated.



Tyler Grummett ( BBSc, BSc(Hons I))
PhD Candidate
Brain Signals Laboratory
Flinders University
Rm 5A301
Ext 66124

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