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Dear SPM Users, I am doing a simple block design experiment where I am have two conditions faces and houses. Both face and house stimuli will parametrically vary in luminance. I would like to use the first order polynomial basis function to see whether there are any areas which are modulated by changes in luminance of faces, but not houses. My main question is how to define the contrast? From what I understand my GLM looks like this: Y = Faces*beta1 + (Faces*Time)*beta2 + Houses*beta3 (Houses*Time)*beta4 + mean*beta5 + error Would it be correct if I defined my contrast as [0 1 0 -1 ] and used a t-test? How can I decide if I need to use a higher order basis function and which order to use? Thank you, Marsha Meytlis Ph.D. student