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Hi David: This sounds like a case in which, for unclear reasons, the intersubject variance is less than intrasubject variance. Thus despite possibly small parameter effects they are consistent across subjects. I suggest looking at the variance images in the random effects data (ResMS.img files). Using imcalc with a function of sqrt(i1) will give you standard deviation. Also look at these images for some fixed effects data. Plot the "time series" (actually subject series) for some voxels using the RanFX analysis in the area of activation. Presumably you'll see consistent effect sizes across subjects. Darren Quoting "Kareken, David A." <[log in to unmask]>: > Hi all, > > I wonder if someone has insights into the following discrepancy between > a random (RFX) and fixed effect (FFX) result in fMRI. The essential > problem is that there is a much stronger RANDOM effects result in > selected areas in which not one single subject shows activation in their > single-subject, fixed effect analysis. There is huge "activation" > spanning the lateral ventricles, and an uncinate focus (all < 0.001), > but NONE of the single subject FFX analyses show anything like this at < > 0.01. > > I would certainly expect much stronger FFX signals than RFX signals, but > have never seen the opposite-- and wouldn't expect any. > > Some quick details are: > n= 7 subects (yes, I know, quite small, but not a final sample). > Blocked design. > FFX analyses with corrections for serial correlation. > The FFX results are a somewhat complicated interaction consisting of > conditions > > 1/1 1/2 1/1 1/2 2/1 2/2 2/1 2/2 > > where the number to left of the ''/" is a drug condition (drug v > placebo) and the number to the right of '/' is a task (1 or 2). > > The contrast images analyzed consist of the drug x task interaction: 1 > -1 -1 1 -1 1 1 -1. > > Thanks for any help, > David K > > David A. Kareken, Ph.D., ABPP/ABCN > Board Certified Neuropsychologist > Associate Professor & Director of Neuropsychology > Department of Neurology (RI-1773) > Indiana University School of Medicine > Indianapolis, IN 46202 > Tel: 317 274-7327 > Fax: 317 274-1337 > > >