[FieldTrip] working with neuromag data

Tavabi, Kambiz TAVABIK at email.chop.edu
Mon Mar 28 20:59:36 CEST 2011

Greetings - I have preprocessed/averaged neuromag data for a group of subjects that I'd like to visualize, compute grandaverage and carry out sensor level statistics on. The only help I managed to find on the Fieldtrip site/list Re: neurmag data concerns getting started e.g., with ft_read_header and ft_read_data. In my case these programs work fine meaning that I can proceed with further analysis. 
On a side, in my limited experience with FT, a major problem I run into frequently is that there is no clear suggestion(s) on how to proceed with data that is not raw. I understand it is impossible to cover all analysis scenarios, but it is often the case that working with CTF, or in particular Elekta system, the data is likely to be in a post-preprocessed phase. Everytime I've tried to work with ft, It seems to me that if I don't start with square one in fieldtrip, it is difficult to figure out how to use downstream programs to work on the data.
That said, in my case I have the output from ft_read_header:

label: {338x1 cell}
         nChans: 338
             Fs: 1000
           grad: [1x1 struct]
           unit: {1x338 cell}
       nSamples: 651
    nSamplesPre: 100
        nTrials: 6
           orig: [1x1 struct]

and output from ft_read_data

[338x651x6] that being channels by samples by number of stimulus averaged epochs. To proceed, ideally I'd like to compute a grandaverage for each condition, visualize them in a multiplot, and carry out sensor level stats. To be able to do this I understand I need the output from ft_timelockanalysis, how do I arrange my data as such? I am assuming it is already in that state. Thanks for your time.

Kambiz Tavabi PhD
Biomedical Imaging Laboratory
The Children's Hospital of Philadelphia
34th Street and Civic Center Boulevard
Philadelphia, Pa. 19104
Tel: 267.426.0302
email: tavabik at email.chop.edu

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