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Hello everyone, I am interested in learning how to model the within-subjects effect of time on a two-stimulus presentation. Each participant viewed two stimuli (CS+, CS-) for a total of ten trials (5 per stimuli). In my first-level FEAT, I have created 2 original EVs and added the temporal derivates to investigate the main effect of stimulus type. Thus, the contrasts: 1 -1 (CS+ > CS-) -1 1 (CS+ < CS-) 1 0 (CS+ > rest) -1 0 (CS+ < rest) 0 1 (rest > CS-) 0 -1 (rest < CS-) We also belive the signal strength in our ROI may be greatly affected by repeated stimulus exposure. For some participants, the signal may habituate, in others it may sensitize. Do I need to create 5 original EVs to represent the 5 trials of stimulus exposure, and then create contrasts that model each potential "shape" of the within-subjects' time effect? I belive I would model a linear signal habituation as: 2 1 0 -1 -2 (and a sensitization model would be the opposite). For a cubic effect, would I model: 2 1 -6 1 2 The interaction of the main effects of stimulus and time are also of interest, as we predict CS- to remain constant over time and CS+ to change. Are all interaction effects analyzed if I select the "interaction" basic shape of an addition EV? Thank you so much for your help, Deane