Hello,
I was wondering whether temporal derivative regressors were orthgonalization w.r.t the original regressor in FSL. There is no mention of this in the design matrix rules:
http://fsl.fmrib.ox.ac.uk/fsl/fslwiki/FEAT/UserGuide#Appendix_B:_Design_Matrix_Rules
However, this paper from Jeanette Mumford suggests that they are:
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0126255
"Similar to SPM, FSL also allows for the modeling of temporal derivatives of regressors to account for minor timing misspecifications. FSL uses a slightly different orthgonalization strategy where the derivative is orthogonalized with respect to both the original regressor and the overall mean. As shown in [2], this approach may still be beneficial in improving the estimate for the regressor of interest, the original regressor, but not as beneficial as only orthogonalizing with respect to the original regressor, as done in SPM."
Thanks,
Ian
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