Hello! I am working on a task were every EV has at least one run with an empty EV. For example, I have four runs, and EV1 occurs only in runs 1 and 2, and EV2 occurs only in runs 3 and 4. This may not be an ideal experiment design, but alas here we are.
So, in the first-level analysis, I’m using the Empty (all zeros) option for an EV. When doing so I get the following error:
"Warning: at least one EV is (close to) a linear combination of the others. You probably need to alter your design.
(Design matrix is rank deficient - ratio of min:max eigenvalues in SVD of matrix is 0)
Contrasts involving these combinations will be set to zero."
The Feat user guide notes I may get that error. However, this appears to be problematic for combining across all runs for a given EV. Using Feat I am combining across all runs but every contrast in my higher-level model is all zeros. I’ve tried adding the lower-level .feat directories, and also just adding the cope images directly. Same result.
I would appreciate any advice on how to address this issue as I can’t find much on message boards. I’m using FSL 6.0. Please let me know if you need any other information. Thank you!
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