Dear FSL experts,
I'm running randomise, as last step in a dual regression, on (resting/task) state of 2 groups that have done different tasks (e.g. rest and task) on two separate days. I have made contrasts of images for each participant e.g. between the two scans using fslmaths, so randomise now should be a very straightforward design on the 3rd level. I've set up randomise as follows:
EVs:
[1 0; 1 0; 0 1; 0 1...]
etc. i.e. two separate EVs that indicate which group a participant is in (the files are e.g. resting on day 1 for each participant)
Contrasts:
[1 1; -1 -1; 1 -1; -1 1]
i.e. both groups together activation/ deactivation and the differences between the groups in both directions
The confusing thing is that for the comparisons between the two groups, randomise does 100 permutations per seed. But for the two groups combined (i.e contrasts [1 1], [-1 -1]), it says "1 permutations required" and only does 1. As a result, the corrp statistical image is empty for this contrast. Even more confusingly - i've tried to run randomise on many possible combinations of task (difference) x day - this happens for most, but not all combinations. Even though looking at the design matrices, they are set up in exactly the same way for each design. There are no error messages in log files (i.e. the ".e" files corresponding to the ".o" files that describe the permutations).
I'd be very grateful for any pointers
Jacquie
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