[FieldTrip] Missing resolution Information in *vhdr causes ft_preprocessing to return only NaNs

[Karch, Julian]

Hi,

thanks for your answer. It seems that I was a little imprecise. Of course the original data set doesn't change but if I export the a data set after setting a new reference in Brainvision Analyzer the header looks like that:

Original header real.vhdr
===============================
Brain Vision Data Exchange Header File Version 1.0
; Data created by the Vision Recorder
[...]
Ch4=Fz,,0.1,µV

 realnewRef.vhdr
===============================
Brain Vision Data Exchange Header File Version 1.0
; Data created from history path: real/Raw Data/New Reference
[...]
Ch4=Fz,Avg,,µV

This was just a test I did with some random data. I don't have acess to the orginal recording for the data sets I want to read in. The header from them look like
Brain Vision Data Exchange Header File Version 1.0
; Data created from history path: passive3101/Raw Data/Filters/New Reference/Attentive
[...]
Ch12=Fz,ref new,,

Like I said what's really strange that I think I was able to preprocess the exact same data set a couple of month ago.

Thanks for your help!

Best,

Julian




Von: fieldtrip-bounces at donders.ru.nl [mailto:fieldtrip-bounces at donders.ru.nl] Im Auftrag von Casper van Heck
Gesendet: Wednesday, January 25, 2012 10:10 AM
An: Email discussion list for the FieldTrip project
Betreff: Re: [FieldTrip] Missing resolution Information in *vhdr causes ft_preprocessing to return only NaNs

Julian,

It is my understanding that the header file doesn't change at all, since Brainvision Analyzer stores all changes either in the 'history' files or temporary files in the history folder. The *.vhdr and *.eeg (and marker files, if any) should be unchanged after preprocessing. Therefore, resolution information should still be there.

Could you check the contents of the header file with notepad?
It should say something like this for every channel under "[Channel Infos]":
Ch27=Fz,,0.0715,µV

Also, you could try to open it with Brainvision Analyzer, and see if that gives an error of sorts.

Sincerely,

Casper van Heck

On Tue, Jan 24, 2012 at 11:54 PM, Karch, Julian <karch at mpib-berlin.mpg.de<mailto:karch at mpib-berlin.mpg.de>> wrote:
Hi,

I'm working on a brainvision EEG dataset  which was preprocessed by someone else using Brainvision Analyzer. One part of his preprocessing was to set a new reference. This processing step makes the resolution information in the *vhdr file disappear. Because of that hdr.orig.resolution=NaN for all channels.  As result of that the lines
                calib = diag(hdr.resolution(chanindx));
      % using a sparse multiplication speeds it up
      dat = full(sparse(calib) * dat);
in read_brainvision_eeg produce only NaN. This again results in trials which only contain NaNs.

I do weekly updates of fieldtrip using svn. Because I'm quite sure if was able to read in, using ft_preprocssing, the excact same dataset, even with the same cfg file, earlier this year I checked the modifications for the last half year or so but I couldn't find any change which could have broken it.
My two questions are. How would you handle this problem? Just plug in some random numbers like 0.1 ? Is this an issue with fieldtrip or am I doing something wrong? Were there any changes to the involved functions which could have changed the behavior in that way?

Thanks in advance!

Best,

Julian

Julian Karch
Research Assistant

Center for Lifespan Psychology
MPI for Human Development
Lentzeallee 94, 14195 Berlin, Germany
phone: +49-30-82406-296<tel:%2B49-30-82406-296>
fax: +49-30-8249939<tel:%2B49-30-8249939>
web: http://www.mpib-berlin.mpg.de


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