Motion regressors - temporal derivatives

Dear Dr. Yan,

first of all, thank you for the wonderful tools you have created, which provide a great service to our community.

I wanted to verify, regarding motion regressors in the nuisance covariates regression: to the best of my understanding, the 12-regressors and 24-regressor models are supposed to include the motion regressors and their temporal derivatives (their value at each time-point minus their value in the previous time-point). However, from the DPARSFA_run.m code, it seems that what is actually used is the value at the current time-point and the value at the previous time-point, instead of their difference.

for example: CovariablesDef.CovMat = [Q1, [zeros(1,size(Q1,2));Q1(1:end-1,:)]];

Is this a mistake? or are the two methods equivalent?

Thank you for your help,


Michael Peer

Hi Michael,

This comes from Dr. Friston's original paper: Friston, K.J., Williams, S., Howard, R., Frackowiak, R.S., Turner, R., 1996. Movement-related effects in fMRI time-series. Magn Reson Med 35, 346-355. You can have a read.

Actually, in regression, the two ways can get the same results.