We are trying to conduct a 2X2 factorial design at the first level of an fMRI study, but are having some difficulty. We are analyzing a memory task where the participant memorizes a list of words, and is then presented a new list where he or she must recall whether the words on that list are either new (not on the first list) or old (from the first list).
We are currently setting up the first level analysis with two factors: word type and correctness. Each factor has two levels: old and new for word type, and correct and incorrect for correctness.
When we run the analysis we end up with a matrix with only one contrast, the average activation. Is there something we are doing wrong that is causing us not to get the other contrasts? The SPM5 manual has an example of using a factorial design at the first level, but the directions are vague. Maybe someone can give us more case specific directions as to how to run the analysis.