clean_flatlines.m

function signal = clean_flatlines(signal,max_flatline_duration,max_allowed_jitter)
% Remove (near-) flat-lined channels.
% Signal = clean_flatlines(Signal,MaxFlatlineDuration,MaxAllowedJitter)
%
% This is an automated artifact rejection function which ensures that 
% the data contains no flat-lined channels.
%
% In:
%   Signal : continuous data set, assumed to be appropriately high-passed (e.g. >0.5Hz or
%            with a 0.5Hz - 2.0Hz transition band)
%
%   MaxFlatlineDuration : Maximum tolerated flatline duration. In seconds. If a channel has a longer
%                         flatline than this, it will be considered abnormal. Default: 5
%
%   MaxAllowedJitter : Maximum tolerated jitter during flatlines. As a multiple of epsilon.
%                      Default: 20
%
% Out:
%   Signal : data set with flat channels removed
%
% Examples:
%   % use with defaults
%   eeg = clean_flatlines(eeg);
%
%                                Christian Kothe, Swartz Center for Computational Neuroscience, UCSD
%                                2012-08-30

% Copyright (C) Christian Kothe, SCCN, 2012, ckothe@ucsd.edu
%
% 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

if ~exist('max_flatline_duration','var') || isempty(max_flatline_duration) max_flatline_duration = 5; end
if ~exist('max_allowed_jitter','var') || isempty(max_allowed_jitter) max_allowed_jitter = 20; end

% flag channels
removed_channels = false(1,signal.nbchan);
for c=1:signal.nbchan
    zero_intervals = reshape(find(diff([false abs(diff(signal.data(c,:)))<(max_allowed_jitter*eps) false])),2,[])';
    if max(zero_intervals(:,2) - zero_intervals(:,1)) > max_flatline_duration*signal.srate
        removed_channels(c) = true; end
end

% remove them
if all(removed_channels)
    disp('Warning: all channels have a flat-line portion; not removing anything.');
elseif any(removed_channels)
    disp('Now removing flat-line channels...');
    try
        signal = pop_select(signal,'nochannel',find(removed_channels));
    catch e
        if ~exist('pop_select','file')
            disp('Apparently you do not have EEGLAB''s pop_select() on the path.');
        else
            disp('Could not select channels using EEGLAB''s pop_select(); details: ');
            hlp_handleerror(e,1);
        end
        disp('Falling back to a basic substitute and dropping signal meta-data.');
        if length(signal.chanlocs) == size(signal.data,1)
            signal.chanlocs = signal.chanlocs(~removed_channels); end
        signal.data = signal.data(~removed_channels,:);
        signal.nbchan = size(signal.data,1);
        [signal.icawinv,signal.icasphere,signal.icaweights,signal.icaact,signal.stats,signal.specdata,signal.specicaact] = deal([]);
    end
    if isfield(signal.etc,'clean_channel_mask')
        signal.etc.clean_channel_mask(signal.etc.clean_channel_mask) = ~removed_channels;
    else
        signal.etc.clean_channel_mask = ~removed_channels;
    end
end