Dear all,
we have an fmri study where we include three independent parametric
modulators. We have the following two questions:
1. Do we have to include them all at the same model or can we run three
different analyses for each one of them, since they are independent from
each other? If both approaches are permissible, what would be the advantage
of each one?
2. If we include the three parametric modulators in the same model, can we
subtract their effect? What would it mean, for example, to define a contrast
of 1 -1 -1 for the three modulators? Would it mean that for a given voxel
we estimate the parametric effect of one modulator minus the effect of the
other two?
Thanks for any help
Giovanna, Dimitrios, Michael, Aron
Cognitive Neuroscience Section
NIH/NINDS
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