[FieldTrip] Wavelet advice

smoratti at psi.ucm.es smoratti at psi.ucm.es
Sun Aug 19 14:19:26 CEST 2012

Dear Peter,

I think you should use 5 cycles as minimum to get stable results. One cycle is not much to estimate the power of your time-freq of interest.



Stephan Moratti, PhD

see also: http://web.me.com/smoratti/

Universidad Complutense de Madrid
Facultad de Psicología
Departamento de Psicología Básica I
Campus de Somosaguas
28223 Pozuelo de Alarcón (Madrid)


Center for Biomedical Technology
Laboratory for Cognitive and Computational Neuroscience
Parque Científico y Tecnológico de la Universidad Politecnica de Madrid
Campus Montegancedo
28223 Pozuelo de Alarcón (Madrid)

email: smoratti at psi.ucm.es
Tel.:    +34 679219982

El 19/08/2012, a las 13:17, Peter Goodin escribió:

> Hi Fieldtrip list,
> I'm attempting to use wavelets to analyse some data collected with a neuromag system (sample rate of 500Hz, pre-trigger period is 200ms, post is 1.6 seconds) but am new to time frequency analysis. I'm interested in lower frequency bins (~4 to 20 Hz). The config settings I've been playing with are as follows:
> cfg.method = 'wavelet';
> cfg.channel = 'MEG';
> cfg.keeptrials = 'yes';
> cfg.foi = [4:1:20]
> cfg.toi = [-.1:.01:1.5]
> cfg.width = x 
> Using a default width of 7, I'm getting large boundary effects leading to a period of ~300ms (400 - 700ms post trigger) of calculated data at 4Hz. I've played with the width and have found that a width of 1 gives only a small amount of boundary effect at the extreme edges and shows a large increase in the frequencies I'm interested in at a time point which corresponds quite nicely with the ERF data also analysed. 
> Having read the Tallon-Baudry (1999) article, material from the tutorials and items from the mailing list, I understand that by using a wavelet width of 1 I've biased my results towards higher temporal vs. spectral resolution, but considering the low range of frequencies I'm interest in, is this a problem? Does using a low width with my cfg.foi set as it is just lead to a large amount of redundant data? 
> Advice on this subject would be greatly appreciated. 
> Peter.
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> fieldtrip at donders.ru.nl
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