[FieldTrip] Wavelet advice

Sheraz Khan sherrykhan78 at gmail.com
Sun Aug 19 22:58:21 CEST 2012

You can always try variables number of cycles may be start with 3 and then
go to 5.
Martinos Center
 On Aug 19, 2012 7:17 AM, "Peter Goodin" <pgoodin at swin.edu.au> wrote:

>  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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