Hi,
I have a question regarding interaction terms in FEAT. I'm analyzing an experiment in which subjects were presented with 3 types of faces preceded by 2 types of primes (primes were presented for 16ms about 150ms before the face; all combinations of faces and primes were used). I've set-up a model that includes EVs for each face and each prime type, as well as the interaction terms (so 11 EVs: 2 primes, 3 faces, 6 prime*face interaction terms). Testing for main effects of primes and faces is no problem, but I'm still thinking about what contrasts to include to fully test for a prime*face interaction. Testing beta's for each interaction term against 0 will find areas that show 'special' activation to a specific combination of prime and face (non-additive effects of being a particular face presented with a particular prime). I was wondering about two things: 1) Would an F-test across these 6 individual contrasts adequately test whether there is ANY prime*face interaction? And 2) Would it make sense to compare beta's for these interaction terms (e.g. a 1-1 contrast for Face1Prime1 Face1Prime2) or would those results be meaningless?
Thanks!
Renske
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