[FieldTrip] (no subject)

[Tzvetan Popov]

Dear Victoria,
the system you are working with is already equipped with two orthogonal planar gradiometer sensors. Thus you should not try to create planar gradients on the basis of the planar gradients. Yet you might want to use the magnetometers only. There you can represent the activity as if it was picked up by planar gradients. Could you please skip the planar transformation bit and redo your analysis?
FieldTrip provides three types of layouts for the Neuromag system: NM306all.lay NM306mag.lay NM306grad.lay. For example if you want to plot magnetometers only you’d specify cfg.layout = 'neuromag306mag.lay’; cfg.channel = 'MEG*1’; Here MEG*1 refers to magnetometers and MEG*2 and MEG*3 would be the two orthogonal planar gradients respectively. Also the neighbours are provided as neuromag306cmb_neighb.mat; neuromag306mag_neighb.mat; neuromag306planar_neighb.mat;. You might consider loading the structure of your choice directly. 
Here is an example tutorial that might help: http://www.fieldtriptoolbox.org/tutorial/natmeg/timefrequency
Good luck,
tzvetan

> Dear Fieldtrip team, 
> 
> I am currently working on data acquired from an elektra system (neuromag). I have done all the preprocessing and the ft_freqanalysis with the gradiometers only. I combined the gradiometers to create planar gradients.However , later when doing the statistics problems occur when i want to specify the channels. The error tells me that no degrees of freedom are found for the analysis. However, when i remove the cfg.channel form the script it runs through without an error. (please see code below). 
> My question is whether the output of the stastistic is correct without specifying the channels? If not, does anybody have suggestions how to fix the problem?
> 
> I have run into similar problems when wanting to plot the time frequency data from the planar gradients after having used ft_combineplanar. Here i cannot find a layout file that suits the output of ft_combineplanar. Thus, i cannot specify a cfg.layout. After ft_combineplanar i have 102 channels, however, the layouts provided by fieldtrip does not fit that number.
> Has anybody run into similar problems? Or does anybody know a possible solution? 
> 
> Thank you very much for any suggestions
> Victoria
> 
> %combine planar
> cfg = [];
> cfg.method ='sum';
> %ComCon = ft_combineplanar(cfg,FreqCon);
> ComIncon = ft_combineplanar(cfg, FreqIncon);
> 
> cfg = [];
> %cfg.channel          = {'MEG'};
> cfg.latency          = 'all';
> cfg.frequency        = [14.5 16];
> cfg.method           = 'montecarlo';
> cfg.statistic        = 'ft_statfun_indepsamplesT';
> cfg.correctm         = 'cluster';
> cfg.clusteralpha     = 0.05;
> cfg.clusterstatistic = 'maxsum';
> cfg.minnbchan        = 2;
> cfg.tail             = 0;
> cfg.clustertail      = 0;
> cfg.alpha            = 0.025;
> cfg.numrandomization = 500;
> cfg_neighb.method    = 'distance';
> cfg.neighbours       = ft_prepare_neighbours(cfg_neighb, data_orig);
> 
> design = zeros(1,size(ComGrad_con.powspctrm,1) + size(ComGrad_incon.powspctrm,1));
> design(1,1:size(ComGrad_con.powspctrm,1)) = 1;
> design(1,(size(ComGrad_con.powspctrm,1)+1):(size(ComGrad_con.powspctrm,1)+...
>   size(ComGrad_incon.powspctrm,1))) = 2;
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