Question about nonparametric statistical testing of coherence differences

[Adrian Bartlett]

Hi Matthew,

While It'll take me a bit to think about the single-condition case, you've
definitely got the right idea for the condition contrast. The
condition-shuffled surrogate data is in fact the null distribution for the
H0: condition 1 = condition 2. Someone please correct me if I'm mistaken.

Adrian M. Bartlett
Perception & Plasticity Laboratory (http://www.yorku.ca/khoffman)
Graduate Program in Psychology
Neuroscience Graduate Diploma Program
Centre for Vision Research
York University
Toronto, Ontario, Canada
(416)736-2100x20997
adrianmb at yorku.ca

On Mon, Nov 16, 2009 at 4:46 PM, Matthew Nelson <nelsonmj at caltech.edu>wrote:

> My question involves a situation in which one is comparing the coherence
> between two signals in two different conditions, and the coherence is
> generally high in both conditions, but we would like to say that the
> coherence is higher in one condition than the other. After some
> thought about this issue, I wonder if shuffling trials between the two
> conditions allows for a fair comparison to be made to the coherence in
> the raw data? For example, if a pair of signals has different relative
> phases in the two conditions, the overall coherence that exists in
> both conditions will be decreased by the trial shuffling. It’s also
> conceivable, though perhaps less likely, that the condition-shuffled
> data could have more coherence than either condition alone. In either
> case, the distribution of the cluster statistics of the coherence
> differences in the condition-shuffled data would certainly provide
> some sort of estimate of a null distribution of the coherence
> difference that does uses the actual data, but since the overall
> coherence values of the condition-shuffled and raw data could be so
> different, is it fair to say that this is a null distribution of the
> difference in coherence between the unshuffled conditions?
>



>
> If you have the time to respond, I’m curious to know what your
> thoughts are regarding this issue and specifically in a situation in
> which it is necessary to assess significance on one session.
> Performing the clustering and shuffling of coherence values across
> sessions obviously avoids this problem. For a test within a session, I
> wonder if it would be possible to use a bootstrapping or jackknife
> method combined with clustering to get a fair estimate of the
> variability of the cluster level statistics and perform hypothesis
> tests using that.
>
> ----------------------------------
> 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
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> http://www.ru.nl/neuroimaging/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/neuroimaging/fieldtrip.
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