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I would like to know if some of you had a similar problem or dilemma. I am computing a correlation map out of a linear model at each voxel. I always thought smoothing images first and getting correlation map is a more or less correct procedure. However, my student computed the correlation out of unsmoothed images and smoothed correlation map later. The smoothed correlation map looks better ! I thought about this a while and I have to conclude that smoothing correlation map is not a bad idea actually. Smoothing is a process of degrading information. So the question is where to degrade information. Do we want to degrade information in the original image or correlation. If we compute correlation out of smoothed images, it is like computing correlation out of something that is already degraded. So smoothing correlation seems to make more sense. But then you worry about random field theory assumptions if you are a random field guy. :) Moo. -- Moo Chung [log in to unmask] http://www.stat.wisc.edu/~mchung Associate Professor Department of Biostatistics & Medical Informatics Waisman Laboratory for Brain Imaging and Behavior University of Wisconsin-Madison