Hello,
I have a design where subjects completed 3 runs within a session. I would like to compare activation within an ROI for Run1 vs Run3. The two runs do not have the same design matrix (so not the same GLM model). However, the two runs contain cognitively similar contrasts (experimental condition 1 vs baseline, condition 2 vs baseline, etc.). I would like to compare these contrasts pairwise to see whether the effect changed from one run to another (as a result of what subjects were exposed to in the intervening Run2).
I have a couple of questions that I would appreciate your input on.
1. Broadly, is there consensus on whether the results from featquery are best plotted as PE/COPE or as percent signal changes? I see different sources recommend different things.
2. More specifically in the context of this experiment, can the two runs only be compared if I look at their percent signal changes (because this is normalized in some way)? Or is it ok to compare their PE/COPE values too? I understand that the units are arbitrary and may not be as intuitive in the latter case, but is it still valid to compare them between runs?
Thanks in advance for your input!
Malathi
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