[FieldTrip] ft_preproc_hilbert questions

[Orion]

Hi Max,

Can you clarify what you mean by a Hilbert time-frequency analysis?
Performing hilbert on a signal will give several different outputs, like
the envelope and phase, and if you want, the instantaneous frequency.  But
I don't understand the meaning of Hilbert time-frequency.

There are ways of calculating hilbert that don't use fft, but as fars as
I'm aware, the hilbert.m that calls fft.m provides a quick way to the
desired outputs.

Orion

On Tue, Oct 28, 2014 at 3:05 PM, Rodrigo Montefusco <
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> 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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