clusterrandanalysis actvsblT

[Andre Bastos]

On a related note, I would like to ask about the clusterrandanalysis option
to set avgovertime = 'yes'

In this case, as far as I am aware, the frequency-space-time-trial quadlets
which clusterrand analysis uses become doublets of frequency-space. In this
case, wouldn't it be possible to compare data periods of different lengths,
as clusterrandanalysis would just average across your baseline period as set
1 and average across the activation period as set 2?

Does the distribution of activation over time get factored in to the
clusterrandanalysis function even when avgovertime is set to 'yes'?

Thanks,

-Andre


-----Original Message-----
From: FieldTrip discussion list [mailto:FIELDTRIP at NIC.SURFNET.NL] On Behalf
Of Eric Maris
Sent: Monday, July 30, 2007 1:50 PM
To: FIELDTRIP at NIC.SURFNET.NL
Subject: Re: [FIELDTRIP] clusterrandanalysis actvsblT

Dear Claudia,



> i have a questions about clusteranalysis comparing baseline and
> activation period. is it really impossible to compare two periods of
> different length? and why? as far as i understand the mean of the
> baseline is used and so you have only one value per frequency anyway.
> can i avoid this problem or do i have to divide my activation period
> into different segments because my baseline period is much shorter?


You are one of many to complain about this feature of clusterrandanalysis.
Nevertheless, you do have to divide your activation period into different
segments. The reason for this has to do with the null hypothesis that is
tested when you use the activation-versus-baseline statistic. This null
hypothesis is the following: The data in the baseline period are drawn from
the same probability distribution (over the spatiotemporal domain) as the
data in the activation period. This null hypothesis only makes sense if the
spatiotemporal dimensionality of the activation and the baseline period are
equal.


Kind regards,

Eric Maris




 

 

dr. Eric Maris

NICI/Biological Psychology and

F.C. Donders Center for Cognitive NeuroImaging

University of Nijmegen

P.O. Box 9104

6500 HE Nijmegen

The Netherlands

T:+31 24 3612651 (NICI)

T:+31 24 3610754 (FCDC)

F:+31 24 3616066 (NICI)

E: maris at nici.ru.nl

MSc Cognitive Neuroscience :www.ru.nl/master/cns/




> thanks in advance
> claudia
> 
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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
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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. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/fcdonders/fieldtrip.