[Mne_analysis] removing channels from .fif structure

sheraz at nmr.mgh.harvard.edu sheraz at nmr.mgh.harvard.edu
Wed Jan 26 09:35:26 EST 2011
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Hi Ellen,

I have encouter the same problem, and written a matlab code to make
grand-average fif file from fif files having different number of sensors.

Feel free to visit my desk any time, I will show you how it works

Sheraz

> Hi all,
>
> For the first few subjects we ran in our MEG-EEG study, we accidentally
> acquired 'junk' data for several non-existent EEG channels. When we
> realized this we changed our parameters to stop acquiring these channels.
> The problem is that now our datafiles have different numbers of channels,
> and this causes us problems when we want to do things like compute the
> grand-average EEG across subjects since, for example, mne_process_raw
> can't average files with different numbers of channels. Obviously it
> doesn't solve the problem to just mark the junk channels as 'bad channels'
> or rename them as 'MISC' channels, because that doesn't actually remove
> them from the data structure--the file still has 400 channels listed
> rather than 398.
>
> We can write our own code to hack around this and grand-average in Matlab,
> but what we'd really like to do to make all of future processing seamless
> for this dataset is to read the average datafiles into Matlab with
> fiff_read_evoked, fix the appropriate fields to delete the junk channels,
> and then use fiff_write_evoked to write it back to a .fif file that has
> the correct number of channels. However it's been a bit challenging to
> figure out what all fields need to be changed in the Matlab structure, so
> I was wondering if anyone had done this before and had suggestions or code
> to share.
>
> Thanks,
> Ellen
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