[FieldTrip] Coherence of single trials

[Sheraz Khan]

Coherence we normally used is event related coherence, which measures the
consistency of phase difference across trials between regions/channels, for
single trial coherence there is an old paper which discuss this
http://brainimaging.waisman.wisc.edu/~lutz/Lachaux_et_all_IJBChaos_2000.pdf

I implemented this long time back let me me know if this is some thing of
your interest.

Sheraz Khan
Martinos Center


On Mon, Nov 26, 2012 at 6:22 PM, Monika Mellem <monikamellem at gmail.com>wrote:

> Dear Fieldtrippers,
>
> I am trying to calculate coherence estimates on individual trials of our
> EEG data and then want to perform a within-subjects statistical test, but
> so far I have not been able to figure out how to do this.  I am able to
> calculate coherence for our 22 subjects and then perform statistics on the
> grand average, so I understand the basic usage of these functions
> (ft_freqanalysis, ft_connectivityanalysis, ft_freqgrandaverage,
> ft_freqstatistics).  But now we want to do statistical testing on
> individual subjects.  Is it possible to keep coherence for individual
> trials in Fieldtrip as they seem necessary for this statistical analysis?
>
> I am setting cfg.keeptrials = 'yes' as an input to ft_freqanalysis, and
> get the cross-spectra of individual trials (I also tried computing the
> fourier spectra but it made no difference in the following step).  However,
> when computing the coherence in ft_connectivityanalysis, Fieldtrip averages
> over the trials.  Is there a way to output coherence for individual trials
> instead?  Please see the full cfg structure settings below.
>
> Also, I did look into the option of cfg.statistic = 'indepsamplesZcoh' as
> an input to ft_freqstatistics since previous posts suggested this was for
> single subject coherence statistics, but our data is paired as the same
> stimulus appears in the 2 conditions we are comparing.  Is there a paired
> test for single subject coherence testing, or should we use cfg.statistic =
> 'depsamplesT'?
>
> Many thanks for any suggestions you may have!
> Monika
> ________________
> Monika Mellem
> PhD Candidate
> Interdisciplinary Program in Neuroscience
> Georgetown University
> Washington, DC
> msm79 at georgetown.edu
> 202-687-2687
>
> ***********************************************************************
> cfg settings for ft_freqanalysis and ft_connectivityanalysis
> ***********************************************************************
> cfg = [];
> cfg.prestim = -0.5;
> cfg.poststim = 1.5;
> cfg.foilim = [2 30];
> cfg.freqrange = 'low';
> % cfg.output     = 'fourier';
> cfg.output     = 'powandcsd';
> cfg.method = 'mtmconvol';
> cfg.keeptrials = 'yes';
> cfg.channel    = {'all'};
> cfg.channelcmb = {refchan 'all'};
>
> cfgcoh=[];
> cfgcoh.channelcmb = cfg.channelcmb;
> cfgcoh.method = 'coh';
>
> v = genvarname(['CRSP_' condition '_low']);
> eval([v '= ft_multitaper_powcoh_EGI(cfg, data);']);  %Wrapper around
> ft_freqanalysis
>
> w = genvarname(['COH_' condition '_low']);
> eval([w '= ft_connectivityanalysis(cfgcoh, ' v ');']);
>
>
>
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>
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