[Eeglablist] question about ITC/ERSP

[Arnaud Delorme]

Dear Pengmin,

another trick for uniform time distribution is to set 'timesout' to -x (x being the subsampling factor). For example x = 1, means that the time-frequency decomposition will be estimated at each time point of the data (same sampling frequency). The help message of newtimef contains more information.

As Makoto mentioned, in all practical applications, this will not have any consequences. However, if you want to coregister EEG time-frequency decompositions with fMRI data for example (and perform instantaneous correlations), it is important to have a uniformly distributed time values.

Best,

Arno

On 11 Dec 2012, at 09:38, Stefon van Noordt wrote:

> Dear Pengmin,
> 
> As mentioned by Makoto, having the time vector of the output not being  
> perfeclty uniformly distributed typically has little to no effect. The  
> lack of uniformity is usually the result of the 'timesout' optional  
> input defaulting to 200 data points.
> 
> However, if you want to ensure that the time vector is perfeclty  
> uniformly distributed, you can set the 'timesout' output when running  
> newtimef. In order to achieve a perfectly uniform distribution,  
> timesout is equal to the sub-epoch window length (returned at the  
> command line when running your newtimef) / srate*1000.
> 
> Hopefully that helps.
> 
> Best,
> 
> Stefon
> 
> 
> 
> 
> 
> Quoting PengMin Qin <qin.pengmin at gmail.com>:
> 
>> Dear all,
>> 
>> I meet one question when I run the "study"- "pre-computer channel measures"
>> to calculate the ITC and ERSP. The epoch is 1100ms, including 200ms
>> pre-stimulus baseline.
>> My parameters for ITC and ERSP is following:
>> 
>> " 'cycles', [1 0.5], 'baseline', [-200 0], 'freqs', [3 4 5 6 7 8 9 10 11 12
>> 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
>> 38 39 40 41 42 43 44 45], 'alpha', 0.05".
>> 
>> I test it, it works. But when I run it, I got one information:
>> "Finding closest points for time variableTime values for time/freq
>> decomposition is not perfectly uniformly distributed."
>> 
>> I am not sure what it means. Are the parameters ok? or There are something
>> wrong?
>> 
>> Thank you very much!!
>> 
>> Best,
>> Pengmin
>> 
> 
> 
> 
> 
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