Dear everyone,
Well, it should depend on the purpose. If it is really "only" about finding voxels whose time course correlates with pupil diameter then you would want to go with a regressor downsampled to the number of volumes. A condition regressor or a parametric modulator thereof (or a convolution of the pupil diameter regressor with the canonical HRF) makes sense only if you are interested in the neural correlates.
> So which is the correct way, and why?
It really depends on the particular aims, so they are not correct or incorrect as such.
Best regards
Helmut
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