[FieldTrip] fieldtrip Digest, Vol 57, Issue 26
rb643 at medschl.cam.ac.uk
Mon Aug 31 13:00:06 CEST 2015
Hi Jan Mathijs,
Thanks for the tip! I think I missed the cross-observational aspect of WPLI and assumed you could also compute it on a trial by trial basis. I will look into the paper and see if I can reproduce it.
However... my data is resting-state that is simply segmented into smaller parts ('trials') to see if there is a metric that is consistent across segments I was interested in looking at individual trials. If WPLI depends on cross-observations this might not the be optimal measure to look at such data as the segments are actually part of a continuous recording. What would be the recommended alternative (that also somewhat tackles the conduction problem)? And more in general, what would be the recommended metric for looking at resting-state connectivity (where there are no real trials)?
Date: Sun, 30 Aug 2015 15:40:46 +0000
From: "Schoffelen, J.M. (Jan Mathijs)" <jan.schoffelen at donders.ru.nl>
To: FieldTrip discussion list <fieldtrip at science.ru.nl>
Subject: Re: [FieldTrip] WPLI for individual trials
Message-ID: <E11D2D76-641E-476C-B78F-6B5446944A33 at fcdonders.ru.nl>
Content-Type: text/plain; charset="Windows-1252"
In general it is not possible to obtain a ?single observation? phase synchrony metric, where this metric is based on the distributional properties (i.e. across observations) of the phase difference. This holds not only for quantities like coherence, but also for WPLI. This being said, one could resort to a leave-one-out strategy, called jackknifing, to get an estimate of how much an individual trial contributes to the overall connectivity estimate. This has been formally described in http://www.sciencedirect.com/science/article/pii/S1053811915003316. Note that in order for this to work, you still need to have multiple trials in your input data. FieldTrip used to support the cfg.jackknife option in ft_connectivityanalysis for the computation of coherence, but I don?t know to what extent this generalizes to WPLI. Also, it?s been a while that I used this (i.e. jackknife) option (for coherence), so I am not sure whether this is still operational in the current version of FieldTrip. (since this option is a bit obscure, we have not done our utmost best to maintain backward-compatibility of the code here, so things may have been broken by general improvements to the code base). If you would like to follow up on this, I suggest you to contact the first author on the paper mentioned (above), I am sure that Craig would be willing to point you into the right direction (as far as he is not yet reading along ? Craig, do you copy, over?).
On Aug 28, 2015, at 7:02 PM, Richard Bethlehem <rb643 at medschl.cam.ac.uk> wrote:
> Dear Fieldtrippers,
> Would anyone be able to tell me how ft_connectivity analysis handles the trials input? Is it possible to get a WPLI connectivity matrix for each individual trial?
> ps: code I am currently using is here: https://github.com/autism-research-centre/fieldtrip_restingState/blob/master/wpli_connectivity.m
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> fieldtrip at donders.ru.nl
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End of fieldtrip Digest, Vol 57, Issue 26
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