Hi SPM community,
Guillaume, Donald

this is a test set up question following up on previous responses.

Assume the following experiment design: block, one task, 2 sessions, 12 participants, one 
custom regressor (R) that models the changing stimulus intensity of the task.

First level Analysis:
I have the following questions: 
(1) Is there task related activity? I am setting this up as shown in the attached diagram 
with a '1' for the task and all zeros for the rest of the parameters.

(2) Does the addition of the custom regressor (R) change my activation? That's a more 
tricky question and I am not quite sure about it. Should I set that one up as a '1 1 
followed by zeros' - contrast or a '0 1 followed by zeros' - contrast?  

Alternatively, should I run 2 models, one including the custom regressor 'R' and one 
without it and I am getting two .mat files in my 1st level analysis, how do I then set up 
my model comparison in SPM? I understand that comparing nested models would be an F-
test, but how do I enter two .mat files in the contrast manager? 

(3) If I figured out the proper way at the subject (1st) level, how do I use this information  
at the second level. Presumably, this depends on the approach at the first level.

Thanks for you help and I hope this will be of interest two others.