Dear users,

I have an fMRI event-related design with 6 conditions = 5 conditions of interest + a baseline condition and an interstimulus interval, varied from 0.5 sec. to 1.5 sec. I want to model my design using the HRF.

My question is: what are the differences in case I model the baseline condition in my design, and if I don't model the baseline condition in my design?

As I understood,

1) if I do model my baseline condition, then my contrast will be (for example condition1>baseline) defined in spm as [1 -1]. In this case the baseline is different from zero.

2) if I do not model the baseline condition in the design, then this is set to zero and my contrast should be (e.g. condition1) [1 0].

As I saw, the results of the main effect of condition1 do not differ between the two designs. Is all this correct? Should I see/expect differences, and if yes, why?

Thank you!

Best,

Ramona