 |
 |
Hi, I've several followup naive questions to this old post on categorical parametric modulators, which I think has been touched on other previous posts, but just to be certain... Would you ever enter each of the four task loads as separate parametric modulators (if yes, what would be the advantage of this) -- or in this case, is it no longer parametric modulation and they should be entered as stick functions as the usual separate regressors, and it's the contrast definitions that test for linear effects, for example? How would you test of quadratic effects then ([-9 -3 0 3 9]?)? In cases where the categories do not fall into an obvious scale (so rather than "task load" we're dealing with "different picture types"), but I'd like to find out which "order" on a scale they would go, is it kosher to enter several parametric modulation definitions in the same model where I vary the numbers assigned to the categories, effectively putting them in different orders on a scale? Or should they be modelled as separate regressors and use contrast definitions to test different orders on a scale? Thanks a lot in advance, g