We have a single group design with two time points. We have used three
approaches to test activation related to the difference between time 1 and 2.
In approach 1, we created two contrast images for each subject at the 1st
level and calculated the difference image using the 'ImCalc' function. We
then took this 'difference' image to the 2nd level and used the One sample t
test option to investigate the group results. In approach 2, we created one
model for each subject at the 1st level, which included the data from both
times 1 and 2. We then created a contrast image that reflected the
difference between time 1 and 2. We then took this 'difference' image to the
2nd level and used the One sample t test option to investigate the group
results. In approach 3, we created two contrast images for each subject at
the 1st level and then took this 'difference' image to the 2nd level and
used the One sample t test option to investigate the group results. We found
that approaches 1 and 2 produced similar results, but that these results
were very different compared to approach 3. Ideas? Is one approach more
'correct' than another? Thanks.
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