[FieldTrip] Jump artifacts not detected

[Es, M.W.J. van (Mats)]

Hi everyone,

I am currently preprocessing my MEG data (removing artifacts). The strange thing is that when looking for jump artifacts I don't find any, but when looking for muscle artifacts I do find jump artifacts. See the code below. Here you can find 5 trials of my data, where in the second trial there is a jump artifact (according to muscle artifact detection): http://dropcanvas.com/yp0d0

------------------------------------------------------------------------------
load('data_short')
%% detect jump artifacts
cfg = [];

% channel selection, cutoff and padding
cfg.artfctdef.zvalue.channel    = 'MEG';
cfg.artfctdef.zvalue.cutoff     = 20; % artifact threshold
cfg.artfctdef.zvalue.trlpadding = 0;
cfg.artfctdef.zvalue.artpadding = 0;
cfg.artfctdef.zvalue.fltpadding = 0;

% algorithmic parameters
cfg.artfctdef.zvalue.cumulative    = 'yes';
cfg.artfctdef.zvalue.medianfilter  = 'yes';
cfg.artfctdef.zvalue.medianfiltord = 9;
cfg.artfctdef.zvalue.absdiff       = 'yes';

% make the process interactive
cfg.artfctdef.zvalue.interactive = 'yes';

[~, artifact_jump] = ft_artifact_zvalue_old(cfg, data_short);


%% Detect muscle artifacts
cfg            = [];

% channel selection, cutoff and padding
cfg.artfctdef.zvalue.channel = 'MEG';
cfg.artfctdef.zvalue.cutoff      = 4; % artifact threshold
cfg.artfctdef.zvalue.trlpadding  = 0; % pad at both sides of trial till it is ... seconds.
cfg.artfctdef.zvalue.fltpadding  = 0;
cfg.artfctdef.zvalue.artpadding  = 0.2; % take 0.2s padding of an artifact (of the part that is above threshold)

% algorithmic parameters
cfg.artfctdef.zvalue.bpfilter    = 'yes';
cfg.artfctdef.zvalue.bpfreq      = [110 140];
cfg.artfctdef.zvalue.bpfiltord   = 9;
cfg.artfctdef.zvalue.bpfilttype  = 'but';
cfg.artfctdef.zvalue.hilbert     = 'yes';
cfg.artfctdef.zvalue.boxcar      = 0.2;

% make the process interactive
cfg.artfctdef.zvalue.interactive = 'yes';

[~, artifact_muscle] = ft_artifact_zvalue_old(cfg, data_short);
---------------------------------------------------------------------------------------

Another thing is that when I only look for jump artifacts in the channel from where I know a jump is present, it actually is detected (try specifying cfg.artfctdef.zvalue.channel    = 'MLF32';)

I am using matlab2013a on the mentat cluster and I use the latest version of FieldTrip. Any help on detecting these jump artifacts is greatly appreciated.

Best,
Mats van Es
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20150708/395794e3/attachment-0001.html>