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

[Casper van Heck]

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>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****
>
> fax: +49-30-8249939****
>
> web: http://www.mpib-berlin.mpg.de****
>
> ** **
>
> _______________________________________________
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