Dear SPMers,

I've got some questions about parametric modulations.
We conducted a study in which participants heard two types of sentences (lets name them c1 and c2) and had to categorized them.
When we built these sentences (during a pretest), we obtained a characteristic (such as degree of familiarity) and we would like to see the effect of this characteristic on activations.
My first idea was to set it as a parametric modulation supposing a linear increase of activations as this characteristic increase (1st order, right ?).
However, I wonder if this parametric modulation is considered as a regressor of non-interest in the design ?
Does it mean that if I set the contrast c1 vs c2 from the design I set the PM, it will mean that the resulting activations will be without the effect of PM ?

Regards,

Alexandre