Neuromag specifications in Fieldtrip

[Jan Mathijs Schoffelen]

Dear Jaakko,

Yes, it is possible to subsequently process your data.

Fieldtrip only needs to know how to interpret your data-matrix. So you
should create a structure, which is recognizable as a fieldtrippish-thingy.

If your input-data is defined in a matrix, you have to specify the following
fields in your input-structure:

input.dimord: this is a string which specifies for each dimension of your
matrix what it means,

If you have time-domain data, with repetitions, it should be
input.dimord = 'rpt_chan_time', with the dimensionality of your data
accordingly.
input.trial = yourdata

If you do not have repetitions, but just an average over trials, 
input.avg    = yourdata 
input.dimord = 'chan_time';

Next you have to define some additional stuff:

input.label: this is a cell-array containing the channel-labels
input.time:  this is a row-vector telling fieldtrip how to convert from
sample to seconds.

If you want to do frequency-analysis, it becomes a bit more tricky; you then
have to convert your data matrix into a cell-array, containing the
single-trial data Nchan*Ntime. You do not need a dimord in that case, but
you need a cell-array of vectors input.time, which specifies the time-axis
for each trial separately.


Hope this helps,

Yours,

Jan-Mathijs



-----Original Message-----
From: FieldTrip discussion list [mailto:FIELDTRIP at NIC.SURFNET.NL] On Behalf
Of Jaakko Sarela
Sent: Monday, March 13, 2006 10:27 AM
To: FIELDTRIP at NIC.SURFNET.NL
Subject: [FIELDTRIP] Neuromag specifications in Fieldtrip

Hi

I'm trying to use the Fieldtrip package to analyse a data from
Neuromag 306 channel device (actually, I only have the 204 gradiometer
channels). 

However, I do not have access to the fif-files, so standard approach
using Fieltrip does not work. I have the following information:
- data file (as a matrix in MATLAB)
- the channel locations (in VVchs_flat.txt, 2D or VVchs.txt, 3D)

Based on this information, is it possible to use the Fieldtrip package
for subsequent analysis? What information do I need to specify, before I
can for instance, plot fields on certain time locations, using
topoplotER?

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D. Sc. (Tech) Jaakko Särelä                            
Helsinki University of Technology        
Laboratory of Computer and Information Science
P.O. Box 5400, FIN-02015 HUT, Finland
http://www.cis.hut.fi/jaakkos
Tel: +358-9-451 4896; Fax: +358-9-451 3277; 
Email: jaakko.sarela at hut.fi
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