[Eeglablist] How to access non-parametric statistics (cluster method Oostenveld and Maris)

[Mikołaj Magnuski]

Dear Felix,

I had a similar problem previously and could not find the cluster
statistics data anywhere in EEGlab structures (perhaps I was
not looking carefully enough - Makoto, is FieldTrip output saved
anywhere in the workspace when doing cluster statistics from
EEGlab?).

When doing cluster statistics EEGlab uses another toolbox -
FieldTrip. If you are unable to dig up the output of this procedure
anywhere in EEGlab I suggest you should perform it in FieldTrip
directly. It's a little bit harder than EEGlab because you don't have
a GUI in FieldTrip, but all the functions are described very well and
some really helpful tutorials are present on the FieldTrip web page
(the page is here: http://fieldtrip.fcdonders.nl/).
There is a function called eeglab2fieldtrip that can transform your
EEG structure from EEGlab to FieldTrip style. All the following
steps can be done according to:
http://fieldtrip.fcdonders.nl/tutorial/cluster_permutation_freq

I have some functions that could help you along the way
(or even automatise the whole procedure), you can con-
tact me if you decide to do cluster statistics directly in
FieldTrip.
Nevertheless, the FieldTrip output should be present somewhere
in the workspace or at least be possible to catch in a script (if not
it is still possible to modify one of the EEGlab functions to return or
eval in your base workspace the information about cluster statistics).

Mikolaj

Pozdrawiam,
Mikołaj Magnuski


2013/6/19 Felix Ball <Felix.Ball at hu-berlin.de>

> Dear list,
>
> Thank you in advance for your help. I currently try to use the STUDY
> function and especially the non-parametric test (Maris and Oostenveld
> cluster statistic). I have an experiment with two conditions and n
> subjects. What I want to know is at which time points and at which
> electrodes the two conditions differ from each other. The difference
> between conditions is investigated on the grand average level.
> I read about a method introduced by Maris and Oostenveld and it seems to
> be perfect for my needs and it is already implemented in EEGLab. What I get
> with EEGLab (see matlab code) is a plot (see figure C1vsC2) with different
> time intervals marked in grey for each electrode. These grey shaded areas
> are, as far as I understood, significant differences between conditions.
> Furthermore, they are in a time range where I expected to find a
> significant difference between conditions. Now I have 2 questions:
>
> 1) I want to access the statistics that are the basis of this plot. Does
> someone know where I can find them or do I have bugs in my code, preventing
> me from accessing the stats variables? I was not able to find any variable
> in my workspace resembling the results shown in figure C1vsC2.
>
> 2) The result I expected (after reading the Maris and Oostenveld paper),
> slightly differs from the result I receive. I expected only one cluster of
> neighbor electrodes and one continuous time interval to be shaded in grey
> in the plot. This cluster- time interval combination would be the maximum
> effect between conditions. However, looking at figure C1vsC2, I see that
> neighbor electrodes have a grey shaded areas, but these areas are not
> necessarily continuous and are not equal for all electrodes. If I just look
> at one electrode, e.g. FC3 (see appendix), I see that the time range is
> sometimes interrupted. How do I know when conditions start and stop to be
> significantly different, if there is not only one time interval of
> significant difference? I need to know the time range because I want to
> pick the mean amplitude (in the time range) for a regression analysis.
>
> Thank you for your help and kind regards. felix
>
>
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