[FieldTrip] extracting individual trial phase connectivity

[Julian Keil]

Dear Hweeling,

if you're looking for a single trial measure of phase relationship, you might want to have a look at the attached papers.
In both papers, single trial phase relationship between cortical sources is described as the phase difference subtracted from the mean phase difference (i.e. Take the phase difference between two channels, average over trials and take the difference between the single trial phase difference and the mean phase difference).

I hope thais goes into the right direction of what you're asking for.

Good luck.

Julian

Keil, J., Müller, N., Hartmann, T., & Weisz, N. (2014). Prestimulus beta power and phase synchrony influence the sound-induced flash illusion. Cerebral Cortex, 24(5), 1278–1288. doi:10.1093/cercor/bhs409


Hanslmayr, S., Aslan, A., Staudigl, T., Klimesch, W., Herrmann, C. S., & Bäuml, K.-H. (2007). Prestimulus oscillations predict visual perception performance between and within subjects. NeuroImage, 37(4), 1465–1473. doi:10.1016/j.neuroimage.2007.07.011


********************
Dr. Julian Keil

AG Multisensorische Integration
Psychiatrische Universitätsklinik
der Charité im St. Hedwig-Krankenhaus
Große Hamburger Straße 5-11, Raum E 307
10115 Berlin

Telefon: +49-30-2311-1879
Fax:        +49-30-2311-2209 
http://psy-ccm.charite.de/forschung/bildgebung/ag_multisensorische_integration

Am 18.09.2014 um 15:32 schrieb Roey Schurr:

> Dear Hweeling,
> 
> Unfortunately I am not yet familiar with the PPC measure, but I guess that being a pairwise phase consistancy measure, it is defined over a set of trials, and can not be calculated for any individual trial (like coherence, or PLV)?
> 
> Just quickly reading through "The pairwise phase consistency: A bias-free measure of rhythmic neuronal synchronization" (Vinck et al., 2010), this seems to be the case.
> 
> Hope this helps,
> roey
> 
> On Thu, Sep 18, 2014 at 3:30 PM, Hwee Ling Lee <hweeling.lee at gmail.com> wrote:
> Dear all,
> 
> I've got a question regarding extracting pairwise phase consistency of individual trials for each subject.
> 
> Using the connectivity analyses tutorial as a reference, I extracted the PPC using the fourier information from the mtmfft (dpss taper).
> 
> Here's an example of my code:
> 
>     cfg                 = [];
>     cfg.output          = 'fourier';
>     cfg.channel         = {'all'};
>     cfg.method          = 'mtmfft';
>     cfg.keeptrials      = 'yes';
>     cfg.tapsmofrq       = 5;
>     
>     % find the index for the c200 condition
>     pre_c200_idx = find(data8.trialinfo == 200);
>     
>     cfg.trials          = pre_c200_idx;
>     cfg.foilim          = [0 100]; % either the full range of frequencies (data2.hdr.Fs/2) or up to 100 Hz
>     cfg.taper           = 'dpss';
>     HLF_pre_c200        = ft_freqanalysis(cfg, data8);
> 
> The PPC is extracted using this code:
> 
>     cfg                 = [];
>     cfg.trials          = 'all';
>     cfg.keeptrials      = 'yes';
>     cfg.channel         = {'all'};
>     cfg.removemean      = 'yes';
>     
>     cfg.method           = 'wppc';
>     cfg.channelcmb       = {cfg.channel, cfg.channel};
>     
>     HLF_pre_c200wppc      = ft_connectivityanalysis(cfg, HLF_pre_c200);
> 
> Although I've specified to keep individual trials, my output is still a 'chan_freq' dimord variable. It does not contain any individual trial PPC information. Is there a way to extract the connectivity for individual trials?
> 
> Thanks.
> 
> Cheers,
> Hweeling
> 
> 
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