[VoxBo] buggy makeGmatrix utility?

[Daniel Kimberg]

Brad said this:
> It seems like the covariates are okay in the .preG file, but have
> changed in the .G file. (I'm only doing this by visual inspection
> because the x-axes of the two files are scaled differentlly, and I'm
> not sure what corresponds to steps of 1 TR in the .preG.) Is this
> diagnostic of something?

The .preG is usually at a higher temporal resolution than your data, and then it's downsampled to the resolution of your data and saved as the G matrix.  So a few things can happen.  If the HRF has stuff going on at frequencies that are too high, that'll be lost, and in some cases you can get weird looking aliasing effects.  It's also possible the sampling rate of the HRF rate is somehow getting lost, although if I recall correctly you usually have to punch that in yourself.

dan