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<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US">Dear
fieldtrip-list,</span></p>
<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US"> </span></p>
<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US">I am
currently trying to figure out a how to solve a specific problem
related to
cluster permutation statistics. I am quite often in a situation
where I want to
test a specific effect against zero.</span></p>
<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US"> </span></p>
<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US">In case of
within subject effects, I can create null-hypothesis data for
each participant
by performing the same kind of analysis with the factor of
interest being
permuted across trials. For each subject, I can then pass both
datasets, the dataset
created on the actual labels as well as the dataset created on
permuted labels,
to the ‘ft_timelockstatistics’ or the ‘ft_freqstatistics’
function in order to
identify significant effects on the group level.</span></p>
<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US"> </span></p>
<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US">For correlation
analysis, there is the possibility to test between-subject
correlations against
zero using the ’ft_statfun_correlationT’ option in
cfg.statistics. The ‘ft_timelockstatistics’
for example then takes care of correlating the data with the
measure of
interest and also performs the cluster-based permutation test.</span></p>
<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US"> </span></p>
<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US">My problem
now is that I don’t know how to perform such a test against zero
on a group
level when not working with correlations but, for example, with
regression coefficients.
</span></p>
<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US"> </span></p>
<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US">In theory,
I know how to create a H0-distribution of sum-t or
number-of-points statistics obtained
from clusters identified in permuted data and I also know how to
correct the clusters
in the real data accordingly. With “in theory” in mean that I
know how to do it
in time or in time-frequency space. The part that I don’t
understand is how
clustering is done additionally in space, that is across
channels.</span></p>
<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US"> </span></p>
<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US">It would be
very helpful if someone could provide a minimum example of
matlab code or refer
me to the respective file or code-sequence in the fieldtrip code
that specifically
deals with identifying clusters in channel-by-time and/or
channel-by-frequency-by-time
data. Apart from the specific problem of testing a given
group-level statistic
against zero, this would of course also help me a lot to
understand better how
clustering in space behaves. </span></p>
<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US"> </span></p>
<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US">Thanks in advance
and best regards</span></p>
<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US"> </span></p>
<p class="MsoNormal"><span style="mso-ansi-language:EN-US"
lang="EN-US">Stefan</span></p>
<p>
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