[FieldTrip] ft_preproc_hilbert questions

[Max Cantor]

I will definitely need to read this, thank you! I am familiar with some of
the differences between Wavelets and Hilbert, such as Wavelet filter kernel
always being Gaussian whereas Hilbert can be varied, and Wavelets being
somewhat more computationally efficient, but I was also under the
impression that they are not fundamentally different. This discussion is
actually something I've been having with a small group here at University
of Michigan so this article may help clarify more details for us.

On Wed, Oct 29, 2014 at 3:26 AM, Eelke Spaak <eelke.spaak at donders.ru.nl>
wrote:

> 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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> >
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> >
> >
> > --
> > Max Cantor
> > Lab Manager
> > Computational Neurolinguistics Lab
> > University of Michigan
> >
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> >
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-- 
Max Cantor
Lab Manager
Computational Neurolinguistics Lab
University of Michigan
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