virtual channel

Tom Holroyd tomh at KURAGE.NIMH.NIH.GOV
Wed Sep 8 16:31:01 CEST 2004

> > There is a quick question: how to read virtual channel
> > data with your software?  Thanks you for your help.
> I presume that you are referring to virtual channels in a CTF dataset?
> As far as I know, virtual channels are stored in the same manner as
> normal MEG and EEG channels ...

For SAM virtual channels, note that you will need to create a dataset
with newDs that contains the virtual channels.  The SAM software
merely stores the weights in the .svl files, and the DataEditor only
displays virtual channels but cannot save them.  Also, the website
here, has a link to a program called
newDs2, which includes a -band option and an -excludeMEG option, which
are helpful for creating virtual channels.  Recall that virtual
channels are only valid in a certain passband, so something like

        newDs2 -band 20 80 -includeSAM stim,20-80Hz.wts -excludeMEG \
                -marker stim -time -.2 .8 src.ds gamma.ds

will do the filtering, clip the time segments (also needs to match the
active window used to create the covariance), and create a dataset
containing only the virtual channels, which will be named V0, V1, ...

Dr. Tom Holroyd
"A man of genius makes no mistakes. His errors are volitional and are
the portals of discovery." -- James Joyce

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