% eeglab2fieldtrip() - This function converts EEGLAB datasets to Fieldtrip

% for source localization (DIPFIT).

%

% Usage:

% >> data = eeglab2fieldtrip( EEG, fieldbox, transform );

%

% Inputs:

% EEG - [struct] EEGLAB structure

% fieldbox - ['raw'|'timelock'|'comp'] for reasons, you can also

% specify 'preprocessing' (raw), 'timelockanalysis' (timelock)

% and 'componentanalysis' (comp).

% transform - ['none'|'dipfit'] transform channel locations for DIPFIT

% using the transformation matrix in the field

% 'coord_transform' of the dipfit substructure of the EEG

% structure.

% Outputs:

% data - FIELDTRIP data structure (see data type functions below)

%

% Note:

% For conversion of low level raw data structures, save the EEGLAB

% dataset and use:

% hdr = ft_read_header( EEGLABFILE );

% data = ft_read_data( EEGLABFILE, 'header', hdr );

% events = ft_read_event( EEGLABFILE, 'header', hdr );

%

% Author: Robert Oostenveld, F.C. Donders Centre, May, 2004.

% Arnaud Delorme, SCCN, INC, UCSD

%

% See also: FT_DATATYPE_RAW, FT_DATATYPE_TIMELOCK, FT_DATATYPE_COMP

% Copyright (C) 2004 Robert Oostenveld, F.C. Donders Centre, roberto@smi.auc.dk

%

% This program is free software; you can redistribute it and/or modify

% it under the terms of the GNU General Public License as published by

% the Free Software Foundation; either version 2 of the License, or

% (at your option) any later version.

%

% This program is distributed in the hope that it will be useful,

% but WITHOUT ANY WARRANTY; without even the implied warranty of

% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

% GNU General Public License for more details.

%

% You should have received a copy of the GNU General Public License

% along with this program; if not, write to the Free Software

% Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

function data = eeglab2fieldtrip(EEG, fieldbox, transform)

if nargin < 2

help eeglab2fieldtrip

return;

end

% start with an empty data object

data = [];

% add the objects that are common to all fieldboxes

tmpchanlocs = EEG.chanlocs;

% get the electrode positions from the EEG structure: in principle, the number of

% channels can be more or less than the number of channel locations, i.e. not

% every channel has a position, or the potential was not measured on every

% position. This is not supported by EEGLAB, but it is supported by FIELDTRIP.

if strcmpi(fieldbox, 'chanloc_withfid')

% insert "no data channels" in channel structure

% ----------------------------------------------

if isfield(EEG.chaninfo, 'nodatchans') && ~isempty( EEG.chaninfo.nodatchans )

chanlen = length(EEG.chanlocs);

fields = fieldnames( EEG.chaninfo.nodatchans );

for index = 1:length(EEG.chaninfo.nodatchans)

ind = chanlen+index;

for f = 1:length( fields )

EEG.chanlocs = setfield(EEG.chanlocs, { ind }, fields{f}, ...

getfield( EEG.chaninfo.nodatchans, { index }, fields{f}));

end

end

end

end

if ~isempty(EEG.chanlocs) && ~isempty(EEG.chanlocs(1).X)

data.elec.elecpos = zeros(length( EEG.chanlocs ), 3);

for ind = 1:length( EEG.chanlocs )

data.elec.label{ind} = EEG.chanlocs(ind).labels;

if ~isempty(EEG.chanlocs(ind).X)

data.elec.elecpos(ind,1) = EEG.chanlocs(ind).X;

data.elec.elecpos(ind,2) = EEG.chanlocs(ind).Y;

data.elec.elecpos(ind,3) = EEG.chanlocs(ind).Z;

else

data.elec.elecpos(ind,:) = [0 0 0];

end

end

data.elec.pnt = data.elec.elecpos;

end

if isfield(EEG, 'chaninfo') && isfield(EEG.chaninfo, 'nosedir') && ~isempty(EEG.chaninfo.nosedir)

switch EEG.chaninfo.nosedir

case '+X'

data.elec.coordsys = 'ctf';

case '-X'

data.elec.coordsys = 'pls';

case '+Y'

data.elec.coordsys = 'ras';

case '-Y'

data.elec.coordsys = 'lpi';

otherwise

end

end

if nargin > 2

if strcmpi(transform, 'dipfit')

if ~isempty(EEG.dipfit.coord_transform)

disp('Transforming electrode coordinates to match head model');

transfmat = traditionaldipfit(EEG.dipfit.coord_transform);

data.elec.elecpos = transfmat * [ data.elec.elecpos ones(size(data.elec.elecpos,1),1) ]';

data.elec.elecpos = data.elec.elecpos(1:3,:)';

data.elec.pnt = data.elec.elecpos;

else

disp('Warning: no transformation of electrode coordinates to match head model');

end

end

end

switch fieldbox

case { 'preprocessing' 'raw' }

data.fsample = EEG.srate;

for index = 1:EEG.trials

data.trial{index} = EEG.data(:,:,index);

data.time{index} = linspace(EEG.xmin, EEG.xmax, EEG.pnts); % should be checked in FIELDTRIP

end

data.label = getchanlabels(tmpchanlocs, 1:EEG.nbchan);

if EEG.trials > 1

res = std_maketrialinfo([], EEG);

data.trialinfo = struct2table(res.datasetinfo.trialinfo);

else

res = struct('subject', EEG.subject, 'condition', EEG.condition, 'group', EEG.group, 'session', EEG.session);

data.trialinfo = struct2table(res, 'AsArray', true);

if isempty(data.trialinfo)

data = rmfield(data, 'trialinfo');

end

end

case { 'timelock' 'timelockanalysis' }

data.avg = mean(EEG.data, 3);

data.var = std(EEG.data, [], 3).^2;

data.time = linspace(EEG.xmin, EEG.xmax, EEG.pnts); % should be checked in FIELDTRIP

data.label = getchanlabels(tmpchanlocs, 1:EEG.nbchan);

case { 'comp' 'componentanalysis' }

if isempty(EEG.icaact)

icaacttmp = eeg_getica(EEG);

end

for index = 1:EEG.trials

% the trials correspond to the raw data trials, except that they

% contain the component activations

try

if isempty(EEG.icaact)

data.trial{index} = icaacttmp(:,:,index); % Using icaacttmp to not change EEG structure

else

data.trial{index} = EEG.icaact(:,:,index);

end

catch

end

data.time{index} = linspace(EEG.xmin, EEG.xmax, EEG.pnts); % should be checked in FIELDTRIP

end

data.label = [];

for comp = 1:size(EEG.icawinv,2)

% the labels correspond to the component activations that are stored in data.trial

data.label{comp} = sprintf('ica_%03d', comp);

end

% get the spatial distribution and electrode positions

tmpchanlocs = EEG.chanlocs;

data.topolabel = { tmpchanlocs(EEG.icachansind).labels };

data.topo = EEG.icawinv;

% Copy weights & sphere, too

data.unmixing = EEG.icaweights*EEG.icasphere;

case { 'chanloc' 'chanloc_withfid' }

otherwise

error('unsupported fieldbox')

end

try

% get the full name of the function

data.cfg.version.name = mfilename('fullpath');

catch

% required for compatibility with Matlab versions prior to release 13 (6.5)

[st, i] = dbstack;

data.cfg.version.name = st(i);

end

% convert EEGLAB channel labels to Fieldtrip channel labels

function label = getchanlabels(tmpchanlocs, indices)

if ~isempty(tmpchanlocs)

label = { tmpchanlocs.labels };

else

label = cell(numel(indices), 1);

for iChan = indices

label{iChan} = num2str(iChan);

end

end