[Mne_analysis] Issue with tfce
Fleur GAUDFERNAU
fleur.gaudfernau at pasteur.fr
Mon Apr 27 10:18:21 EDT 2020
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Hello,
I am actually wondering if something might be wrong with the way the tfce is performed.
Almost all values in my array are negative, and I get only positive t values. I get exactly the same result when performing a test with tfce on X and on -X. Which means that the sign of the t values is wrong (for some of them at least), unless I'm missing something.
(I'm using 2-tailed cluster permutation test with tfce = dict(start=0., step=0.5)).
Kind regards,
Fleur
________________________________
De : mne_analysis-bounces at nmr.mgh.harvard.edu <mne_analysis-bounces at nmr.mgh.harvard.edu> de la part de Dan McCloy <dan at mccloy.info>
Envoyé : vendredi 24 avril 2020 16:01
À : Discussion and support forum for the users of MNE Software
Objet : Re: [Mne_analysis] Issue with tfce
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Hi Fleur,
Quoting from Smith & Nichols 2009 (https://doi.org/10.1016/j.neuroimage.2008.03.061):
"By default, voxels that were originally negative will be given zero TFCE score. However, if it is desired to apply the enhancement to both negative and positive values, the original image can be simply negated, passed through the enhancement, re-negated and combined (via addition) with the positive enhancement."
As far as I know, MNE-Python's implementation does *not* do this for you automatically.
-- dan
Daniel McCloy
https://dan.mccloy.info
Research Scientist
Institute for Learning and Brain Sciences
University of Washington
‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Friday, April 24, 2020 7:48 AM, Fleur GAUDFERNAU <fleur.gaudfernau at pasteur.fr> wrote:
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Dear mne community,
I'm doing 1 sample permutation cluster t-tests (two tailed) between 2 conditions.
Most of the values in my array data (difference between conditions) are negative, hence I'm expecting negative T values (which is what I get when I'm not using tfce). However, when using tfce, the test returns only positive T values. Is there a way to overcome this issue?
Thanks in advance,
Fleur
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