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% 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