eog artifact rejection

[Christian Hesse]

Hi Samer,

try sorting your ICs by the (absolute) correlation of their waveforms
with the EOG signal -> the one or two components with the highest
correlation are those that should be removed.

If you encounter problems in getting this to work, please let me know.
Christian



On 20 Feb 2007, at 17:06, Sameer Walawalkar wrote:

> I am interested in removing blink artifacts.  Unfortunately, with
> fieldtrip component analysis, it is difficult to identify the
> independent component corresponding to blinks by visual inspection
> due to the short timecourse over which they are presented (trial
> length).
>
> There are essentially two errors:
> 1> ??? Error using ==> timelockanalysis
> data has variable trial lengths, you specified not to accept that !
> 2> fdcomp.cohspctrm does not exist.
>
> I tried to follow instructions under  independent component
> analysis (ICA) to remove ECG artifacts replacing eog for ecg. (I
> did not do any resampling).  (Is this a good idea?)
>
> So I did,
> % go back to the raw data on disk and detect the peaks in the EOG
> channel,
> cfg = same.old.cfg.used.for.component.analysis.of.data;
> cfg.artfctdef.eog.pretim = 0.25;
> cfg.artfctdef.eog.psttim = 0.50-1/1200;
>
> [cfg, artifact]          = artifact_eog(cfg); (found 11 artifacts)
>
>
> % preprocess the data around the peaks, i.e. read the segments of
> raw data containing the EOG artifact
> cfg           = [];
> cfg.dataset   =  'JD_012507_Beeps_One.fif';
>  cfg.datatype  = 'continuous';
> cfg.padding   = 10;
> cfg.dftfilter = 'yes';
> cfg.blc       = 'yes';
> cfg.trl       = [artifact zeros(size(artifact,1),1)];
> cfg.channel   = {'MEG' 'EOG'};
> data_eog      = preprocessing(cfg)
>
> % decompose the ECG-locked datasegments into components, using the
> previously found (un)mixing matrix
> cfg           = [];
> cfg.topo      = compRR_orig.topo;
> cfg.topolabel = compRR_orig.topolabel;
> comp_eog      = componentanalysis(cfg, data_eog);
> selecting 307 channels
> baseline correcting data
> starting decomposition using predetermined mixing matrix
> total time in componentanalysis 1.2 seconds
>
>
> % compute a frequency decomposition of all components and the ECG
>
> cfg      = [];
> timelock = timelockanalysis(cfg, comp_eog);
> applying preprocessing options
> ??? Error using ==> timelockanalysis
> data has variable trial lengths, you specified not to accept that !
>
> % compute a frequency decomposition of all components and the ECG
>
> cfg            = [];
> cfg.method     = 'mtmfft';
> cfg.output     = 'fourier';
> cfg.foilim     = [0 100];
> cfg.taper      = 'hanning';
> cfg.pad        = 'maxperlen';
> freq           = freqanalysis(cfg, comp_ecg);
>
>
> % compute coherence between all components and the ECG
> cfg            = [];
> cfg.channelcmb = {'all' 'ECG'};
> cfg.jackknife  = 'no';
> fdcomp         = freqdescriptives(cfg, freq);
>
> Even though I get computing cross-spectral densities message, I do
> not get .cohspctrm.
>
> fdcomp =
>
>        dimord: 'chan_freq'
>          freq: [1x155 double]
>         label: {307x1 cell}
>     powspctrm: [307x155 double]
>           dof: [307x155 double]
>           cfg: [1x1 struct]
>
>
> Sorry for the long email, and thanks for your help.
>
> sameer
>

----------------------------------------------------------------------
Christian Hesse, PhD, MIEEE

F.C. Donders Centre for Cognitive Neuroimaging
P.O. Box 9101
NL-6500 HB Nijmegen
The Netherlands

Tel.: +31 (0)24 36 68293
Fax: +31 (0)24 36 10989

Email: c.hesse at fcdonders.ru.nl
Web: www.fcdonders.ru.nl
----------------------------------------------------------------------




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