Olga Prilipko wrote:
> 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?
1 -1 -1 1
> 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?
Assuming it was the same order as above, but then you had the same 4
columns for session 2, it would be
1 1 -1 -1 -1 -1 1 1
First 4 entries are the difference in speed in a session, the first
session. Then one tests to see if there's a difference between sessions
in this difference.
> Thank you very much!
> Olga Prilipko
William D. Penny
Wellcome Trust Centre for Neuroimaging
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