Dear SPMers,

I would very much appreciate your help on how to correctly specify the  
contrasts to test for an interaction.

1) If I were to analyze a 2x2 factorial experiment data with A factor:  
speed of presentation and B: novelty of stimulus, I would have 4  
regressors for A1B1 A1B2 A2B1 and A2B2. What would be the correct way  
of testing for a speed x novelty interaction in this case?
2) If I wanted to test for a speed x session interaction (if the  
experiment has 2 sessions) what would be the procedure for that?

Thank you very much!

Olga Prilipko