[color=#000000]Hi Alexandra,[/color]
[color=#000000]They are very similar but not identical, I believe the main difference is that SPM extracts the [b]1st eigenvariate[/b] 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 [b]average[/b] 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. [/color]
[color=#000000]Best[/color]
[color=#000000]Alfonso[/color]
[i]Originally posted by Alexandra Muratore:[/i][quote]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![/quote]
[color=#000000]They are very similar but not identical, I believe the main difference is that SPM extracts the [b]1st eigenvariate[/b] 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 [b]average[/b] 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. [/color]
[color=#000000]Best[/color]
[color=#000000]Alfonso[/color]
[i]Originally posted by Alexandra Muratore:[/i][quote]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![/quote]