Fwd: RE: clusterrandomization for 2 epochs separately

Olga Sysoeva olga at GRAPHICMIND.INFO
Wed Oct 22 17:12:27 CEST 2008 

Thank you all for your answer. I perfectly understand what you wrote.

Unfortunately early effect I believe in is what only our group is found
therefore we could not use the former study and take the electrode and
latency from them.

I also know the way how I can represent our data using the conventional
t-test analysis.

I just want to use here the clusterrandomization analysis for more logical
and tense description of the results.

My question is does the usage of clusterrandomization on the 2 epochs
separately make sense here. If you think that the conventional t-test is
more suitable here, I’ll stand on it.

 

Best Regards,

Olga.

 

  _____  

From: FieldTrip discussion list [mailto:FIELDTRIP at NIC.SURFNET.NL] On Behalf
Of Eric Maris
Sent: Wednesday, October 22, 2008 5:43 PM
To: FIELDTRIP at NIC.SURFNET.NL
Subject: Re: [FIELDTRIP] Fwd: RE: clusterrandomization for 2 epochs
separately

 

Dear Nic,

 

 

I have a quick answer for you, and would be please to heard people's comment
on it. If you had a priori reason to belive something would happen for these
electrodes and time-window, you don't need cluster analysis at all. All the
solutions to the multiple-comparison problem are to be used in exploratory
situation, when you don't know what to expect. If you had specific
hypothesis, don't be shy: test them directy with a T-Test on the average
voltage for a pre-determined time-window. 

Think about it, if you did expect these effects to be there, you could had
create a montage with only one or two electrodes, and the
multiple-comparison problem would not apply at all.

Your understanding makes me happy! I couldn’t have formulated it any better.

 

Eric Maris

 

 

 

 

 

 


Hope this help,

Nic

************************************
Nicolas Robitaille, candidat Ph.D
Département de Psychologie
Université de Montréal
C.P. 6128, succursale Centre-ville
Montréal, Québec H3C 3J7
Tel.: 514-343-6111 x2631
Fax: 514-343-5787
************************************


> Date: Wed, 22 Oct 2008 12:10:01 +0100
> From: olga at GRAPHICMIND.INFO
> Subject: [FIELDTRIP] Fwd: RE: clusterrandomization for 2 epochs separately
> To: FIELDTRIP at NIC.SURFNET.NL
> 
> > Dear Eric, 
> > I would like to consult with you about some our ERP data and
> > application of the clusterrandomization to it. 
> > 
> > I am writing now the article about ERP signs of visual change
> > detection. 
> > 
> > We have ERP to the "deviant" and "standard" stimuli sampling rate
> > 512 Hz, 64 channels (Biosemi), 12 subjects. 
> > 
> > If we use the paired-wise t-test to compare the ERPs' amplitudes in
> > response to standard and deviant stimuli separately for each
> > electrode and time point (and plot it see the picture at the end of
> > the letter) we can see 2 (4) time regions of differences. But
> > application of clusterrandomization analysis to these data (latency
> > 0-500 ms) reveal only late cluster as significant, the early cluster
> > is marginally significant (p=0.1). But I really believe in this early
> > effect (120-160 ms), it is very important for our paper. When I run
> > the clusterrandomization analysis on the narrowed epoch (0-300 ms) I
> > got the early cluster significant. But the problem than that I loose
> > the late effect, which is also worth mentioning in the paper. 
> > 
> > Therefore, I would like you opinion about the possibility to use the
> > clusterrandomization analysis separately on the 2 epochs of interest,
> > let say first 250 ms post-stimulus (0-250 ms) and next (250-500 ms). 
> > 
> > In this case there would be two significant clusters... 
> > Best Regards, 
> > 
> > Olga Sysoeva 
> > P.S. 
> > 
> > I also used different parameters for clusterrandomization (ndis,
> > nchannels) but this does not change the results much. 
> > P.P.S. 
> > 
> > Additional material 
> > The paired-wise t-test was used to compare the ERPs' amplitudes in
> > response to standard and deviant stimuli separately for each
> > electrode and time point. 
> > 
> > The standard and deviant ERPs comparison reveals 2(4) intervals of
> > significant differences: 
> > 
> > Fig.1. At this weird J picture we see the boxes of significant
> > differences between standard and deviant ERPs for each time point (x
> > axis) and electrode (y axis). 
> > Olga Sysoeva, PhD
> > Institute of Higher Nervous 
> > Activity and Neurophysiology
> > Russian Academy of Sciences
> > 5a Butlerova str.
> > Moscow 117485
> > RUSSIA
> > tel.: (7-095)-3347011, 
> > fax:(7-095)-338-85-00. 
> > 
> > Links:
> > ------
> > [2] http://www.ru.nl/master/cns/
> > 
> > 
> 
> ----------------------------------
> The aim of this list is to facilitate the discussion between users of the
FieldTrip toolbox, to share experiences and to discuss new ideas for MEG and
EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html
and http://www.ru.nl/fcdonders/fieldtrip.

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The aim of this list is to facilitate the discussion between users of the
FieldTrip toolbox, to share experiences and to discuss new ideas for MEG and
EEG analysis.

http://listserv.surfnet.nl/archives/fieldtrip.html

http://www.ru.nl/fcdonders/fieldtrip/

----------------------------------

The aim of this list is to facilitate the discussion between users of the
FieldTrip toolbox, to share experiences and to discuss new ideas for MEG and
EEG analysis.

http://listserv.surfnet.nl/archives/fieldtrip.html

http://www.ru.nl/fcdonders/fieldtrip/


----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/fcdonders/fieldtrip.
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