Hi everyone,
I am doing a study involving 17 subjects performing two tasks A and B at two
different difficulty levels Fast (F) and Slow (S). Four scans were done with
the subjects performing tasks A and B at difficulty level F (x 2 times):
{AF1,AF2,BF1,BF2 (4 EVs)}
and at level S (x 2times): {AS1,AS2,BS1,BS2 (4 EVs)}.
From my understanding of the FSL procedure I have to do a Fixed Effect
analysis across sessions first to summate the tasks to generate 4 different EVs:
A(F){summation of AF1 and AF2},
B(F){summation of BF1 and BF2},
A(S){summation of AS1 and AS2} and
B(S){summation of BS1 and BS2}.
Additionally since I want to compare the difference within subject
performing the same task at two different paces I did the following
mid-level contrasts using fixed effect to generate two contrast images:
A(F) vs A(S)
B(F) vs B(S)
Thus far I had no problems. I then wanted to do a one-sample t-test across
17 subjects to find out which significant regions are activated during each
individual tasks.
I tried to perform a mixed effect analysis using FLAME 1 using individual
COPE files as my input. While I got a statistical output with A(F), B(F),
A(S), B(S) across 17 subjects I did not get a statistical output (only image
output) when my input files were the contrast files {A(F) vs A(S)} or {B(F)
vs B(S)}. This was not the case when I used Fixed Effect for the higher
level analysis as I got a statistical cluster output for all inputs. I had
done the same analysis with SPM before and it worked with the GLM analysis
there.
My questions for you are:
1) can I use contrast COPE files like I generated in the mid-level as my
input for higher level analysis?
2) if I can why does the FLAME analysis not work for these images and only
Fixed effect analysis works?
3) is there a better way of doing this analysis given that I want to see
the differences within subject and then do a one-sample t-test across
subjects to generate my final result?
Any help will be greatly appreciated.
Thanks
Suman
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