Dear FSL List,
I have been running fsl on a delayed response task using an epoch which is
the length of every trial and subsequently adding a parametric modulator of
load (3,4,5 or 6). I have two groups and im using a very simple [1 -1] [-1
1] contrast. I usually run feat first since, it is fairly simple to do so
and create the design matrix, and then using the same design.mat and
design.con files I run randomise using the 4D concatenated
cope1/filtered_func_data.nii.gz file. The script I use in randomise is this:
randomise -i cope1.feat/filtered_func_data.nii.gz -o
ADHD_CON_vs_CON_PM_67_exc_cov -d design.mat -t design.con -v 6 -T -V -n 100
I use a variance smoothing of 6 since that is the smoothing I used on the
first level analyses I did for this dataset and I'm using -T for TFCE. I ran
randomise only for a 100 permutations in order to save some time and get
preliminary results.
My problem is that I keep getting different results in feat than the results
I get in randomise. When I say different results that means that usually
feat is more 'sensitive' since I do get activation using it but then I lose
it when I run randomise for exacty the same design matrix. I find this very
odd since randomise is supposed to be quite robust and the results
replicable. Even more so, some people would argue that with TFCE I should
obtain at least similar activation patterns than those found in feat using
the arbitrarily selected threshold of z=2.3 for the cluster based analysis.
Id be very happy if you could help me understand this.
Thank you very much for your help.
Best wishes.
--
Andres
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