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Dear Michael, > These latter two contrasts give considerably > different SPMs compared to the ones that isolate a single effect. This > combination of results suggest to us that the [1 -1] and [-1 1] > contrasts may be more sensitive to relevant task > associated changes than a more typical contrast settings used for > event-related experiments? Does this make statistical sense, and are > there any published methodological references which document and further > describe such a phenomenon? Yes, in general the sensitivity of an event-related design to different contrasts will vary as a (complex) function of SOA, event ordering and the presence of null events. Relevant refs are: Friston, K.J., Zarahn, E., Josephs, O., Henson, R.N.A. & Dale, A. (1999) Stochastic designs in event-related fMRI. Neuroimage, 10, 607-619. Josephs, O. & Henson, R.N.A. (1999) Event-related functional magnetic resonance imaging: modelling, inference and optimization. Philosophical Transactions of the Royal Society, B, 354, 1215-1228. If you search the list archive for 'event related efficiency' or 'optimisation' there are also details of the MGH seqefficiency program and further discussion of this topic. Best wishes, Geraint -- Dr. Geraint Rees Wellcome Advanced Fellow, Lecturer, Division of Biology 139-74, Institute of Neurology, California Institute of Technology, University College London, Pasadena CA 91125 London WC1N 3BG voice 626-395-2880 020-7833-7472 fax 626-796-8876 020-7813-1420 web http://www.klab.caltech.edu/~geraint -- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%