In my current data set, I have some subjects with pretty severe dropout in the ventral striatum, while other subjects have no dropout. Since group-level analyses in SPM only include voxels that ALL subjects have, I end up with a lot less voxels in the ventral striatum for my group-level contrasts. So, when I extract ROI data from my SPM.mat file for a group-level contrast, Marsbar only seems to be averaging activity in voxels that all subjects have (from what I can tell).
Is there any way to average activity in an ROI on a subject by subject basis in MarsBar? In other words, rather than averaging activity only in voxels that ALL subjects have, can I get the average activity for all the voxels each subject has?
My ultimate goal is to take all the voxels a subject has in the ventral striatum and then average the activity together. I tried creating an ROI for each subject with all the voxels they had in the ventral striatum, and then extracting the data using Marsbar. However, that approach yielded the exact same result as using a ROI for the whole ventral striatum and extracting the data.
Thanks so much for any help!