[Eeglablist] PCA topo plots with EEGLAB

Arnaud Delorme arno at sccn.ucsd.edu
Thu May 5 03:55:56 PDT 2005


The following plugin on the EEGLAB plugin page (to be saved in the plugin
directory (under subfolder pca for instance) will also compute PCA
components (instead of ICA)):

http://www.sccn.ucsd.edu/eeglab/eegplugin_pca.m (plugin)
http://www.sccn.ucsd.edu/eeglab/contrib.html#Plugins (web page)

Note that PCA components (except maybe for the first one) are usually not
biologically plausible and their associated scalp maps look like
checkerboards.

Arno

> Brian -
>
> ICA unmixing in EEGLAB can easily be replaced by PCA or, more typically,
> PCA-based decompositions, as follows:
>
> EEG.data = data;   % 2-D or 3-D array
> EEG.nbchan = size(EEG.data,1); % multiplexed by channels
> EEG.icaweights = PCA_matrix;
> EEG.icasphere = eye(EEG.nbchan); % null entry = identity matrix
>
> Here, the PCA_matrix should be that used to *un*mix the data, e.g. for
> PCA, the matrix inverse (inv() or pseduo-inverse, pinv()) of the product
> of the eigenvector matrix times the eigenvalue diagonal matrix. The
> pseudo-inverse is needed when the number of components retained is less
> than the number of data channels (EEG.nbchan). Any kind of  linear
> transform of the data can be handled by EEGLAB in this way. (Note: As
> the product of the icasphere and icaweights matrices is always used in
> EEGLAB, you could also reverse the order of matrix assignments above).
>
> Scott Makeig
>
>
> Brian Roach wrote:
>
>> I am wondering about importing PCA data (from matlab) to EEGLAB so
>> that I can use some of its plotting functions.  Is there is a format
>> template for importing data from a matlab array (if so, could someone
>> please send it to me)?  If anyone has a better idea about how I should
>> do this, please let me know.  I am using Jurgen Kayser's matlab code
>> for PCA (found here:
>> http://psychophysiology.cpmc.columbia.edu/mmedia/mmedia.html).
>>
>> Thanks for any info and help.
>>
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>
>
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