[FieldTrip] ft_preproc_hilbert questions

Eelke Spaak eelke.spaak at donders.ru.nl
Wed Oct 29 08:26:29 CET 2014


Dear all,

The following paper by Andreas Bruns might offer some highly relevant
background:

Bruns (2004) J Neurosci Meth
Fourier-, Hilbert- and wavelet-based signal analysis: are they really
different approaches?
http://www.sciencedirect.com/science/article/pii/S0165027004001098

Best,
Eelke

On 28 October 2014 21:50, Rodrigo Montefusco <rmontefusco at med.uchile.cl> wrote:
> To where I understand, yes. Just remember that is amplitude and not power (you probably knew that). I should remark that the filter part is tricky and critical.
>
> Best
>
> On Tue, Oct 28, 2014 at 3:48 PM, Max Cantor <mcantor at umich.edu<mailto:mcantor at umich.edu>> wrote:
> Ah, so if I do a narrow BP filter around a single frequency, looped over however many frequencies I want, and then restructure the looped data into a dimensionally similar matrix as powspctrm in a fieldtrip-type structure, I could effectively turn it into a TFR?
>
> On Tue, Oct 28, 2014 at 3:05 PM, Rodrigo Montefusco <rmontefusco at med.uchile.cl<mailto:rmontefusco at med.uchile.cl>> wrote:
> Hi Max,
>
> to what I understand, the output of Hilbert will be the amplitude of the input signal (envelope). If you want to use that information, then the only step you should add before is a very good and sweet narrow band filter (as narrow as you want your frequency bins). Then, the filter design is the hard part, because you need a filter that is able to filter out other frequencies without introducing any kind of artifact.
>
> Hopefully someone else has something to add, or if I'm missing any stuff.
>
> Best
>
> Rodrigo
>
> On Tue, Oct 28, 2014 at 2:16 PM, Max Cantor <mcantor at umich.edu<mailto:mcantor at umich.edu>> wrote:
> Hi,
>
> So this is not a specific method-based question, but something more general.
>
> I've been slowly reading through bits and pieces of Mike Cohen's 'Analyzing Neural Time Series Data' book, in an attempt to gain a better understanding of how things like Fourier Transform, Wavelets, and Hilbert work on a more fundamental level.
>
> Fieldtrip does not have a built in Hilbert time frequency analysis (that I'm aware of), but from having read through that chapter of Cohen's book I've been able to effectively create a hilbert analysis of my own.
>
> However, I was wondering if it would be possible to use ft_preproc_hilbert (setting cfg.hilbert = 'complex', 'real', etc. in ft_preprocessing) to do this in a more efficient and fieldtrip-compatible way. It seems I can use this setting to get the analytic signal, phase, power, and other things, but since this is on raw/epoched data, there is no obvious way I can think of to apply a time or frequency series as in the other TFRs. It seems I could either write a fieldtrip function from scratch, which I'm not prepared to do, or write a function to reformat fieldtrip data to work using the Cohen function, and then output it back into a fieldtrip function, which would be fine but I'm more interested to know if the ft_preproc_hilbert function can do what I want more efficiently.
>
> So boiling it down, my questions are:
>
> 1. Can cfg.hilbert parameter for ft_preprocessing (or ft_preproc_hilbert called directly) be used as an ad hoc hilbert TFR, and if so what ad hoc steps would one need to take?
>
> 2. If it cannot be used this way, what situations is it meant for?
>
> --
> Max Cantor
> Lab Manager
> Computational Neurolinguistics Lab
> University of Michigan
>
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>
> --
> Max Cantor
> Lab Manager
> Computational Neurolinguistics Lab
> University of Michigan
>
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