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Dear SPM list, I'm planning on running an experiment with conditions A and B in two different sessions pre and post manipulation. My task would proceed as follow, Participants will run one session (pre manipulation) with 50% A trials and 50% B trials. While in the scanner we will perform a manipulation on them (approx 5 min). And inmediately we will run a second session similar to the first one. My hypothesis is that Pre A = Pre B, and Post A != Post B, which should translate in a significant interaction. And that Post A > Pre A. Are this statiscally valid contrasts, assuming that Post A and Pre A occur in different sessions? I've been advised to not compare trials across sessions though in this case there is no other way possible. Cheers and thanks in advance, Luis.