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<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'>Dear Marco,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
lang=EN-US style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'>You
have posted this message once before. This was during my holidays, so I did not
reply then. When I returned from holidays, I forgot to send you a reply. My
apologies for this.<o:p></o:p></span></font></p>
<div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span lang=EN-US
style='font-size:12.0pt'><br>
<br>
I am using Cluster Randomization Analysis (CRA) on scalar data and I would like
to be sure that the procedure is correct. </span>Results are plausible, but
since this is not the canonical use of CRA, I would like to have your feedback.
<br>
<br>
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.m to
obtain the electrode structure, and by transforming the data structure by hand
to mimick the output of the tutorial data, CRA Within-Subjects case.<br>
The result for each condition is a structure like this:<br>
<br>
data1 = <br>
<br>
label: {39x1 cell}<br>
fsample: 500<br>
elec: [1x1 struct]<br>
cfg: [1x1 struct]<br>
dimord: 'repl_chan_time'<br>
individual: [9x39 double]<br>
time: 1<br>
<br>
I then performed CRA with the following parameters:<br>
cfg=[];<br>
cfg.statistic='depsamplesT';<br>
cfg.alphathresh=0.05;<br>
cfg.makeclusters='yes';<br>
cfg.minnbchan=2;<br>
cfg.neighbourdist=1;<br>
cfg.clusterteststat='maxsum';<br>
cfg.onetwo='twosided';<br>
cfg.alpha=0.05;<br>
cfg.nranddraws=500;<br>
cfg.channel={'all'};<br>
[clusrand]=clusterrandanalysis(cfg,data1,data2);<br>
<br>
My questions are:<br>
1) Is this procedure correct or are there specific parameters for scalar data?<br>
<br>
<font color=blue><span style='color:blue'><o:p></o:p></span></font></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
lang=EN-US style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'>As
far as I can see, this analysis is correct. However, these are not scalar data,
because you have observed the EEG on 39 sensors. If you had observed the data
on a single sensor only (and a single time point), then the data would have
been scalar (i.e., expressible as a single number for every experimental
condition).<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
lang=EN-US style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
lang=EN-US style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span lang=EN-US
style='font-size:12.0pt'>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?<font color=blue><span style='color:blue'><o:p></o:p></span></font></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
lang=EN-US style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
lang=EN-US style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'>This
is not possible with clusterrandanalysis. However, this is possible with one of
the new statistics functions in Fieldtrip that will replace both
clusterrandanalysis and sourcestatistics. The function of interest for you is
timelockstatistics, and you should have a look at the help information for the
lower-level function statistics_montecarlo (which is called by
timelockstatistics). However, provided that you use more than 500 draws from
the permutation distribution, don’t expect major changes in the output.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span lang=EN-US
style='font-size:12.0pt'><br>
<br>
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: <br>
<br>
clusrand from clusranderfcpFICvsFCorig.mat has two fields with incorrect
dimensions that give errors when plotted: <br>
stats: [151x1x301 double] <br>
raweffect: [151x1x301 double]<br>
<br>
while they should be <br>
stats: [151x301 double]<br>
raweffect: [151x301 double]<br>
<br>
<font color=blue><span style='color:blue'><o:p></o:p></span></font></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
lang=EN-US style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
lang=EN-US style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'>Yes,
this is an inconvenient format for plotting. I will change it.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span lang=EN-US
style='font-size:12.0pt'><br>
and a problem with plotting (once the little error corrected): I attach the
figure that I plotted by following the instructions in the tutorial. </span>I
am using Matlab 7 and FieldTrip version 20060731. Can you help me with this?<font
color=blue><span style='color:blue'><o:p></o:p></span></font></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
lang=EN-US style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'>My
hunch is that these strange plotting results are a due to inappropriate limits of
the color axis. You should use the same limits for all plots in a series. Also,
choose the color limits symmetric around zero. By-the-way, I was surprised to
see a time axis in your plots. I thought you only had a spatial dimension.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
lang=EN-US style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
lang=EN-US style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
lang=EN-US style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'>Good
luck,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
lang=EN-US style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Bookman Old Style"><span
lang=EN-US style='font-size:12.0pt;font-family:"Bookman Old Style";color:blue'>Eric
Maris<o:p></o:p></span></font></p>
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