[FieldTrip] multitaper and NaN

[Silvia Pagano]

Hi all,
thank you a lot for your suggestions. The thing that was not clear to me
was the parameter that expresses Raleigh frequency in Fieldtrip. Now it
makes much more sense.

Thanks again, I will try with your suggestions and see what happens

Cheers

Silvia



On Tue, Jun 26, 2012 at 6:49 PM, Rodrigo Montefusco <
rmontefusco at med.uchile.cl> wrote:

> Hi Silvia,
>
> As I see in your config, you are using 5 cycles per frequency
> (cfg.t_ftimwin  = 5./cfg.foi;), that means that for 2 Hz you need at least
> 500ms * 5 = 2.5 secs epochs to resolve that frequency.
> 1.- you can try with longer epochs...(eg 5 secs)
> 2.- using less cycles per freq.
>
> please someone correct me if I'm wrong
>
> cheers
>
> Y
>
> On Tue, Jun 26, 2012 at 12:04 PM, Silvia Pagano <silvia.pagano at unitn.it>wrote:
>
>> Dear list subscribers,
>>
>> I am an ERPer looking for the first time into the world of time-frequency
>> analysis. I am trying to perform some multitaper analysis on a data set.
>> Ideally I would like to perform similar analysis as described in a paper by
>> Gould et al (2011) on Journal of Neurophysiology. (i.e. in their own words
>> "Time-frequency analysis was performed on
>> all epochs using a multitaper approach (2–30 Hz, 0.5-Hz steps, 500-ms
>> temporal smoothing window, 2-Hz frequency resolution)" )
>>
>> I have epochs from -1100 ms to 100 time locked to the stimulus onset and
>> I am trying to replicate the analysis they did. The problem is that I got
>> boundary effects on all my conditions, namely I obtain NaN in the extreme
>> 100 ms of the time window for all frequencies and for very low frequencies
>> (e.g. 2-4Hz) I have no data in the whole time window. I thought I had time
>> windows large enough to avoid boundary effects, however there must be
>> something I am missing in my code.
>>
>> Here's what I did following the tutorial:
>>
>> cfg = [];
>> cfg.output     = 'pow';
>> cfg.channel    = 'EEG';
>> cfg.method     = 'mtmconvol';
>> cfg.foi        = 2:2:30;
>> cfg.t_ftimwin  = 5./cfg.foi;
>> cfg.tapsmofrq  = 0.4*cfg.foi;
>> cfg.toi        = -1.1:0.02:0.1;
>> cfg.pad        = 'maxperlen';
>> TFRmult = ft_freqanalysis(cfg, data);
>>
>>
>> Does anyone have a clue on this?
>>
>>
>> Thank you very much
>>
>> Silvia
>> --
>> __________________________________
>>
>> Silvia Pagano PhD student
>> CIMeC - Center for Mind/Brain Science
>> Corso Bettini, 31 38068 Rovereto (TN)
>> Tel. +39 0464 808709
>>
>>
>> _______________________________________________
>> fieldtrip mailing list
>> fieldtrip at donders.ru.nl
>> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>>
>
>


-- 
__________________________________

Silvia Pagano PhD student
CIMeC - Center for Mind/Brain Science
Corso Bettini, 31 38068 Rovereto (TN)
Tel. +39 0464 808709
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