mwaskom/moss

Issues relating to Design Matrix

mwaskom opened this issue · 1 comments

mwaskom commented

Here are some issues I have run into and want to think more about:

  • Downsampled timeseries are shifted with respect to the hires timeseries. This is because the downsampling also shifts the predicted response forward to correspond to the middle of the TR. This makes some sense but also might be surprising. I want to rethink whether this should be done and whether it is being done in the most obvious way. Further, need to think about this in the context of an FIR model.

  • Should the default oversampling over the design matrix/hrf kernel be changed? It inherited 16x oversampling from FSL but that means it is hard to specify very short events with a given duration. I think it might make sense to change the parameterization to give a hires time bin (not relative to TR) and make the default 60 to correspond to the refresh rate of a typical monitor. Stimulus events will generally be limited by that resolution.

  • Needing to give the HRF functions a hires stimulus to get a simple predicted response is confusing outside of the context of a DesignMatrix.

  • A DesignMatrix with high-pass filtering but demean=False will have a zero mean because the filter removes a constant trend. This is confusing. Do we want to add the column means back in after filtering and then allow the presence of a constant trend be determined by demean?

mwaskom commented

Project archived; improved design matrix code is in lyman.