[FieldTrip] Connectivity comparison across conditions

[Vitória Piai]

Hi Jose,

Just adding two helpful references that further clarify Jan-Mathijs's point:

"Fourier-, Hilbert- and wavelet-based signal analysis: are they really 
different approaches?"
http://www.ncbi.nlm.nih.gov/pubmed/15262077

"Comparison of Hilbert transform and wavelet methods for the analysis of 
neuronal synchrony"
http://www.sciencedirect.com/science/article/pii/S0165027001003727

Cheers, Vitoria

> On 7/9/2015 7:24 AM, Schoffelen, J.M. (Jan Mathijs) wrote:
>> Jose,
>>
>>> Regarding the time-resolved PLV, isn't it different to do it with 
>>> mtmconvol, which in my view provides a TFR, than with a time signal 
>>> based on the Hilbert transform which estimates instantaneous phase.
>>>
>>> My doubt is that the time-resolved PLV will need three or four 
>>> cycles for good spectral estimation, and two things can happen:
>>> 1 - I analyse non-overlapping chunks and get a low number of 
>>> time-points.
>>> 2 - I analyse highly overlapping segments and thus a lot of PLV 
>>> estimations but not really independent from each other and therefore 
>>> biasing the comparison to other conditions
>>>
>>> With the Hilbert derived transform I would theoretically have as 
>>> many independent estimates of the PLV, right?
>>>
>>> Is there a caveat in my line of thought? I might be missing 
>>> something here…
>>
>> The thing you are missing here, is that the Hilbert transform also 
>> integrates over time to get an ‘instantaneous’ estimate of phase and 
>> amplitude (in other words, there’s nothing instantaneous about it). 
>> The difference with Fourier based methods is that you explicitly have 
>> to set the time window when doing a short window FFT, and for the 
>> Hilbert transform (which by the way in MATLAB is computed through a 
>> Fourier transform as far as I remember) one only can guess about how 
>> independent the time samples are from one sample to the next. Note, 
>> that temporal overlap is not so much an issue when doing statistical 
>> inference by means of permutation tests.
>>
>> Best,
>> Jan-Mathijs
>>
>>
>> Jan-Mathijs Schoffelen, MD PhD, Senior researcher
>>
>> Max Planck Institute for Psycholinguistics
>> Donders Centre for Cognitive Neuroimaging
>>
>> E-mail: j.schoffelen at donders.ru.nl <mailto:j.schoffelen at donders.ru.nl>
>> Telephone: +31-24-3614793
>>
>> http://www.hettaligebrein.nl
>> http://www.fieldtriptoolbox.org
>>
>>
>>
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>

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