[Mne_analysis] 3-byte raw data buffers - best way to deal with eeg data interference

[Matti Hamalainen]

On Mar 30, 2009, at 2:12 PM, Linnaea Stockall wrote:

> Hi again,
>
> Every problem I solve just seems to bring me a new one in its stead.
> I'm trying to use mne_compute_raw_inverse
> Thanks to Matti & Alex, I managed to solve the trigger line problem.
> But now I'm getting the error:
> Reading data Cannot process buffers of data type: 3
>
> This seems to refer to data buffers in the raw EEG data (at least
> that's the only reference to buffers I can find in the manual). I'm
> not actually interested in EEG data. We recorded from a few reference
> electrodes so we could use the data to remove eye blinks, but
> otherwise we don't want to use the EEG channels at all. Is there some
> way to tell mne_compute_raw_inverse to use MEG data only and ignore
> any EEG buffers (just adding --megonly didn't work)? Or is there
> something I have to do convert the 3-byte buffers to 4? The EEG
> channels were recorded by the CTF system, and bundled with the MEG
> data.
>
> Thanks to anyone who has an idea of how to fix this.

Hi Linnaea,

Data type 3 does not mean three bytes but rather 32-bit integers. The  
mne_compute_raw_inverse in the new MNE 2.6 handles 32-bit data. If you  
wan to continue using the MNE version 2.5.2 you can convert the CTF  
data to floats (and maybe downsample):

mne_process_raw --raw <orig> --projoff --save <converted file>

This also does the default 40-Hz lowpass. You can include --lowpass, -- 
highpass, --filteroff, and --decim options as desired to control the  
output.

- Matti






-------------

Matti Hamalainen, Ph.D.
Athinoula A. Martinos Center for Biomedical Imaging
Massachusetts General Hospital
Building 149, 13th Street, Mailcode 149-2301
Charlestown, MA 02129-2060
USA

e-mail          msh at nmr.mgh.harvard.edu
Tel             +1 617 726 0323
FAX             +1 617 726 7422



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