Thank you for the response! I read the paper and I understand that the integration of motion parameters as covariates might not be beneficial when the motion parameters are correlated to the task paradigm. This definately makes sense to me.
However, in practice. SPM does contain an orthogonalization step. So if the design matrix is orthogonalized, this effects will be diminished right? Are the confound-regressors not orthogonalized? When does orthogonalization become a problem? I thought I read that the only problem about orthogonalization can occur when the regressors are not linearly independent anymore. But then the regressors might still be correlated... Can somebody comment on this?
Thank you!
Debby
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