[FieldTrip] Reference to non-existent field 'mom' in ft_connectivityanalysis

[Eelke Spaak]

Dear Davide,

ft_connectivityanalysis requires individual trials, and the
combination of 'fourier' - 'pcc' is the only combination there that
results in individual trial estimates. Internally, I think the 'pcc'
beamformer basically computes the exact same filters as DICS, it just
has a somewhat different (i.e. more flexible) approach to data
bookkeeping, allowing straightforward filtering of individual trials.

Best,
Eelke

On Tue, 14 May 2019 at 15:27, Davide Sometti
<davide.sometti-1 at studenti.unitn.it> wrote:
>
> Dear community,
>
> I’m trying to perform connectivity analysis (Matlab 2018b, FieldTrip 2018-12-11), in order to obtain the absolute part of the imaginary coherence. Here are the steps that I’ve used in order to perform it.
>
> 1-     First I performed the frequency analysis, on the single condition (not showed), and on all the conditions together
>
> cfg = [];
>
> cfg.channel    = chn;
>
> cfg.method     = 'mtmfft';
>
> cfg.output     = 'powandcsd';
>
> cfg.taper      = 'dpss';
>
> cfg.keeptrials ='no';
>
> cfg.keeptapers ='no';
>
> cfg.tapsmofrq  = 3;
>
> cfg.foi        = [6; 11; 16; 21; 26; 40];
>
> data_freq_all  = ft_freqanalysis(cfg, data_reject_all);
>
>
>
> 2-     I computed the beamformer filters based on the entire data
>
> cfg=[];
>
> cfg.method='dics';
>
> cfg.frequency=6;
>
> cfg.grid=lf;
>
> cfg.grid.pos=pos;
>
> cfg.grid.tri=tri;
>
> cfg.headmodel=hdm;
>
> cfg.senstype     = 'meg';
>
> cfg.dics.projectnoise = 'yes';
>
> cfg.dics.lambda       = '5%';
>
> cfg.dics.keepfilter   = 'yes';
>
> cfg.dics.realfilter   = 'yes';
>
> cfg.dics.keepcsd       = 'yes';
>
> cfg.dics.keepmom       = 'yes';
>
> cfg.dics.fixedori     = 'yes';
>
> sourceAll = ft_sourceanalysis(cfg,data_all);
>
>
>
> 3-     I've then performed the source analysis on each of the four conditions, using the precomputed filter
>
> cfg.grid.filter=sourceAll.avg.filter;
>
>
>
> source_pre_incl=ft_sourceanalysis(cfg,data_pre_incl);
>
> source_pre_excl=ft_sourceanalysis(cfg,data_pre_excl);
>
> source_post_incl=ft_sourceanalysis(cfg,data_post_incl);
>
> source_post_excl=ft_sourceanalysis(cfg,data_post_excl);
>
>
>
> 4-     Finally I’ve performed the connectivity analysis
>
>
>
>
>
> cfg=[];
>
> cfg.method  ='coh';
>
> cfg.complex = 'absimag';
>
> source_conn = ft_connectivityanalysis(cfg, source_pre_incl);
>
>
>
> When I try to run the connectivity analysis I get this error, and I cannot go further in the analysis.
>
>
>
> Reference to non-existent field 'mom'.
>
>
>
> Error in univariate2bivariate (line 225)
>
>       sizmom = size(data.mom{data.inside(1)});
>
>
>
> Error in ft_connectivityanalysis (line 449)
>
>         [data, powindx, hasrpt] = univariate2bivariate(data, 'mom', 'crsspctrm', dtype, 'cmb', cfg.refindx, 'keeprpt', 0);
>
>
>
>
>
> I’ve tried different solution, changing output for the frequency analysis and method for the beamforming, like follow:
>
>
>
> 'fourier' - 'pcc'
>
> 'powandcsd' - 'pcc'
>
> 'fourier' - 'dics'
>
> The combination fourier and pcc was the only one that worked, among the 4, the others always gave me the same error, as above. I’m wondering why even if I’ve specified cfg.keepmom=’yes’, this one is not present in the structure after the source analysis.
>
> Anyone that could help me?
>
> Davide S.
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> https://doi.org/10.1371/journal.pcbi.1002202

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