Hi all,

When reviewing 2nd-level results in CONN, my understanding is that you can extract individual connectivity values by opening the results in "Results Explorer" and then selecting "Import Values" > "Other clusters of interest or ROIs (select mask/ROI file)", and then importing these values. Assuming this is correct, how is this different from opening the SPM.mat file representing the same contrast and extracting first-level eigenvariates using a mask? Will these result in the same values or different ones, and if so, how are they different?

Thanks!

Hi Alexandra,

They are very similar but not identical, I believe the main difference is that SPM extracts the 1st eigenvariate from the selected voxels (1st- component from a Singular Value Decomposition of the data, i.e. a weighted combination of the values across all voxels, weighted so that the resulting variable explains the maximum variance possible across all voxels) while CONN extracts simply the average across the selected voxels. That said, if the region is relatively small and/or homogeneous, the 1st-eigenvariate is in practice very similar to the average, while the region is large or non-homogeneous these two approaches will differ more clearly. 

Best
Alfonso
Originally posted by Alexandra Muratore: