clusterrandanalysis on scalar values + problem with topoplotER

Marco Buiatti marco.buiatti at GMAIL.COM
Fri Aug 4 11:22:06 CEST 2006


Dear FieldTrippers,

I am using Cluster Randomization Analysis (CRA) on scalar data and I would
like to be sure that the procedure is correct. Results are plausible, but
since this is not the canonical use of CRA, I would like to have your
feedback.

I have 9 subjects, two experimental condition for each subject, and 39
channels. For every subject, channel and condition, I computed an exponent
alpha of the power law that better fits the temporal long-range
autocorrelations in the data, i.e. a scalar value between 0.5 and 1.5. I
transformed the data in a format suitable to CRA by using
eeglab2fieldtrip.mto obtain the electrode structure, and by
transforming the data structure by
hand to mimick the output of the tutorial data, CRA Within-Subjects case.
The result for each condition is a structure like this:

data1 =

         label: {39x1 cell}
       fsample: 500
          elec: [1x1 struct]
           cfg: [1x1 struct]
        dimord: 'repl_chan_time'
    individual: [9x39 double]
          time: 1

I then performed CRA with the following parameters:
cfg=[];
cfg.statistic='depsamplesT';
cfg.alphathresh=0.05;
cfg.makeclusters='yes';
cfg.minnbchan=2;
cfg.neighbourdist=1;
cfg.clusterteststat='maxsum';
cfg.onetwo='twosided';
cfg.alpha=0.05;
cfg.nranddraws=500;
cfg.channel={'all'};
[clusrand]=clusterrandanalysis(cfg,data1,data2);

My questions are:
1) Is this procedure correct or are there specific parameters for scalar
data?
2) Is there a way to compute the null distribution by considering all
possible reassignments of the conditions instead of the Monte Carlo
approximation - in this case it would be feasible because all possible
reassignments should be 2^9, right?

Last point, when I ran the examples on the tutorial data in the Cluster
Randomization Analysis section, Within-Subjects case, I found out a little
error:

clusrand from clusranderfcpFICvsFCorig.mat has two fields with incorrect
dimensions that give errors when plotted:
stats: [151x1x301 double]
raweffect: [151x1x301 double]

while they should be
stats: [151x301 double]
raweffect: [151x301 double]

and a problem with plotting (once the little error corrected): I attach the
figure that I plotted by following the instructions in the tutorial. I am
using Matlab 7 and FieldTrip version 20060731. Can you help me with this?

Thank you and have a good day,

Marco


--
Marco Buiatti - Post Doc

**************************************************************
Cognitive Neuroimaging Unit  - INSERM U562
Service Hospitalier Frederic Joliot, CEA/DRM/DSV
4 Place du general Leclerc, 91401 Orsay cedex, France
Telephone: +33 1 69 86 77 65    Fax: +33 1 69 86 78 16
E-mail: marco.buiatti at gmail.com    Web: www.unicog.org
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