Hi FSL experts,
I am trying to run a PPI analysis using an "A minus B" approach. I am following instructions as per http://fsl.fmrib.ox.ac.uk/fsl/fslwiki/PPIFAQ.
I have two conditions in the task, and I created an EV text file that codes condition A as 1 and condition B as -1.
My EVs are:
1 - Cond A - Cond B
2 - Physio time course of seed
3- PPI interaction
4 - Cond A + Cond B
However, when I generate the glm in Feat GUI, I am getting the warning:
"Problem with processing the model: 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 1.3329e-08). Contrasts involving these combinations will be set to zero."
Should I be concerned about this warning? Is there an issue with the model set-up, or could this have something to do with the EV (stimuli) themselves?
Thank you,
Michelle
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