[FieldTrip] request for 4d users

[Rojas, Don]

Dear Jan-Mathijs,

We do not routinely digitize EEG electrodes, but I will look and see if we still have an old test dataset that we acquired to learn the process years ago. Like Yuval, we use Eugene Kronberg's pdf4D matlab object code. To get the labels (e.g., FP1), as opposed to the names (e.g., E1), we do something like this:

pdf=pdf4D('c,rfhp0.1Hz')
hdr=get(pdf,'header')
idx=channel_index(pdf,'EEG','name')

Variable idx holds the indices for the EEG channels. Then, for a specific channel label, if they are entered by the user, you can get it this way:
hdr.channel_data{idx(1)}.chan_label

In this case, that label is FP1 and the channel name is E1, in the dataset that I am looking at now. But, other than the index association, there is no standard convention for association of names and labels. The names are a 4d convention. The labels are user specified in the template configuration file used for acquisition.

Or if looking for the indices of a specific EEG label, this way:
idx=channel_index(pdf,'FP1','label')

Don

On Oct 31, 2012, at 1:03 AM, jan-mathijs schoffelen wrote:

Dear community and 4d-users in particular,

I am in the process of implementing more robust support in the fileio module to deal with simultaneous MEG/EEG measurements using the 4D-neuroimaging system. Specifically, I want to improve the reading of EEG electrode positions, when these have been digitized using the Polhemus in combination with the 4D acquisition software. This question has been raised on this list over a year ago by Margit Schönherr (who kindly sent me a dataset to work with: thanks Margit), but it would be really helpful if I could benefit from your knowledge/input. At the moment FT can extract electrode positions from the header, but it is based on reverse engineering based on 1 dataset only. Therefore I would like to ask you whether you could send me some (as small as possible) datasets, which contain digitized electrode positions (in combination with the corresponding config and hs_file). This would be much appreciated.
On a related note, Margit's dataset contained electrode positions in combination with their labels according to the 10/20 convention. Does anybody know whether information is stored in the file-header that links the named electrodes to the generic naming scheme 'E1'...'Ex'?

Thanks for any input,

JM


Jan-Mathijs Schoffelen, MD PhD

Donders Institute for Brain, Cognition and Behaviour,
Centre for Cognitive Neuroimaging,
Radboud University Nijmegen, The Netherlands

Max Planck Institute for Psycholinguistics,
Nijmegen, The Netherlands

J.Schoffelen at donders.ru.nl<mailto:J.Schoffelen at donders.ru.nl>
Telephone: +31-24-3614793

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-----------------------
Don Rojas, Ph.D.
Associate Professor of Psychiatry
U. of Colorado Denver Anschutz Medical Campus
Director, UCD Magnetoencephalography Lab
13001 E. 17th Pl F546
Aurora, CO 80045
303-724-4994

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