[Eeglablist] about the backprojection of component on original EEG channel

[Arnaud Delorme]

Dear Tulu,

> Is it possible to back-projection of each component to origin EEG 
> channel and compare the origin raw EEG data under EEGlab GUI?
>
Yes, for this you can use
1) Tools > Component ERP image, and specify on channel to project the 
component to in the first edit box of the GUI.
2) Tools > Component ERPs > With component Map. In this function, 
specify the component you want to plot. The function will plot the 
component ERP enveloppe along with the data ERP envelope (the "envelope" 
of a multichannel data set is the maximum and minimum value at each time 
point).
3) Use command line function calls. For instance, to plot the 
contribution of component 1 (in red) to all channels (in blue), use

figure; comp = 1; plottopo([mean(EEG.data,3) 
EEG.icawinv(:,comp)*mean(EEG.icaact(comp,:,:), 3)], EEG.chanlocs, 
EEG.pnts, [EEG.xmin EEG.xmax 0 0]);

(note: you must first import a channel location file, extract epochs 
from the data and compute ICA).
See the EEGLAB script tutorial for the meaning of the fields of the EEG 
structure

http://www.sccn.ucsd.edu/eeglab/scripttut/script_tutorial.html#EEG

> I have 18 channels EEG and after ICA training, I have 18 components. 
> It is some difficult that I must convert individual component to 
> origin EEG channel and compare it, also check this component is 
> artifact or not. So how to do this more efficient ?
>
Using the menu "Tools > Reject data using ICA > Reject component by 
maps" usually provides enough information to visually reject components. 
See the main EEGLAB tutorial for some hints on rejecting artifactual 
components at

http://www.sccn.ucsd.edu/eeglab/maintut/ICA_decomposition.html#9.4._Studying_and_removing_ICA

Arno
-- 

* Arnaud Delorme <http://www.sccn.ucsd.edu/%7Earno>, Ph.D.* , SCCN, 
UCSD, San Diego, USA

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