[Eeglablist] artifacts in time freq plots

Makoto Miyakoshi mataothefifth at yahoo.co.jp
Thu Jun 3 19:14:54 PDT 2010


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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