[Eeglablist] artifacts in time freq plots

Arnaud Delorme arno at ucsd.edu
Mon Jun 7 08:04:18 PDT 2010


Dear Makoto,

yes, this is a good suggestion. We will implement it.
Thanks a lot,

Arno

On Jun 3, 2010, at 7:14 PM, Makoto Miyakoshi wrote:

> Dear Ondrej and Arno,
>
> Yes. When I read your command line I actually missed that you used the
> optional input 'basenorm' which I have never used. I should have  
> been more
> careful to check the input parameters before seeing the results. I
> apologize that my initial comment was misleading too.
>
> One thing I also notice is that you used 'nfreqs' and 'padratio'  
> togetehr
> but they are mutually exclusive and nfreqs is used when both are  
> input.
>
> This is suggestion for Arno, but is it possible in future to show  
> what is
> actually calculated in what way when presenting the figure,  
> especially when
> optional parameters are used? I know newtimef shows input parameters  
> and
> calculation processes, but I mean for the sake of drawing attention  
> of new
> users (and careless user like me) it may be helpful to present  
> additional
> lines like 'Caution: basenorm is on; the shown result is devided by
> deviation of baseline period' or 'Caution: nfreqs and padratio are  
> both
> input; nfreqs is used and padratio is neglected'. I know these rules  
> are
> written in the help lines, but just for enabling a quick check.
>
> Makoto
>
>
> --- ondrej lassak <tehuberpro at gmail.com> wrote:
>
>> Hey guys
>>
>> Arnaud is right (thx for the code analysis) its just a numerical
>> artifact, which is impossible to occur on a real life EEG, so Makoto
>> you can chill :D
>>
>> This time I added to the ideal sinusoid pseudo white noise and since
>> it adds non 0 variance the numerical artifact cannot occure and one
>> get sweet line in the TF plot even when using base subtraction
>>
>> try this code to see it for yourself:
>>
>> fs=2048%samples/s
>> t=linspace(0,8,8*2048);%samples
>> f=6%Hz
>>
>>
>> x=.05*sin(2*pi*f*t);
>> x1=.05*sin(2*pi*f*t*2);
>> x=[x(1:8*2048/2) x1(1:8*2048/2)];
>> x=x+.01*rand(1,length(t))
>>
>>
>> figure; [ersp,itc,powbase,times,freqs,erspboot,itcboot] = newtimef(x,
>> 8*2048, [-500 8000], 2048, 0,'baseline',[NaN],'basenorm','off',
>> 'maxfreq' ,19,'nfreqs',150,'padratio', 32, 'scale', 'abs');
>> set(gcf,'Name',('original signal no baseline adjustment'))
>>
>> figure; [ersp,itc,powbase,times,freqs,erspboot,itcboot] = newtimef(x,
>> 8*2048, [-500 8000], 2048, 0,'baseline',[5000 6000],'basenorm','off',
>> 'maxfreq' ,19,'nfreqs',150,'padratio', 32, 'scale', 'abs');
>> set(gcf,'Name','baseline adjusted [5000 6000] ms')
>>
>>
>>
>> figure; [ersp,itc,powbase,times,freqs,erspboot,itcboot] = newtimef(x,
>> 8*2048, [-500 8000], 2048, 0,'baseline',[2000 5000],'basenorm','off',
>> 'maxfreq' ,19,'nfreqs',150,'padratio', 32, 'scale', 'abs');
>> set(gcf,'Name','baseline adjusted [2000 5000] ms')
>>
>>
>>
>>
>>
>> On Wed, May 12, 2010 at 4:46 AM, Makoto Miyakoshi
>> <mataothefifth at yahoo.co.jp> wrote:
>>> Dear Ondrej,
>>>
>>> I replicated your results. This is shocking actually.
>>> I also found that the problem is probably in baseline subtraction
>> because
>>> when I set 'baseline', NaN, the result seems right.
>>>
>>> Makoto
>>>
>>>
>>> --- ondrej lassak <tehuberpro at gmail.com> wrote:
>>>
>>>> I fed the TF analysis single sinusoid 6 and 12Hz and the TF plot
>>>> shows
>>>> multiple specral lines (more than two).
>>>> How can one rely on the TF when it introduces such massive
>> artifacts
>>>> both in
>>>> pure FFT spectrogram and Wavelet scalogram?
>>>> Or am I doing something wrong? When only one freq during the whole
>>>> time span
>>>> is present the TF plots look like really bad moira and the
>> presence
>>>> of the
>>>> freq is apparent only from the summation over time (left from the
>>>> main
>>>> plot).
>>>>
>>>>
>>>> The matlab report with function calls and resulting pictures is
>>>> attached
>>>> below (no scripts embedded in the html).
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>
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