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Hi Cyril, Thanks for the wisdom. That is what I thought, but it is nice to know that is the case. If I may, I have one more questions: Do you know of any references that address the issue of spacial smoothing for irregular volumes (not necessarily an "imaging" reference). I have tried to find this, but have had difficulty. Thank you once again very much for your time and thoughts. Regards, Shaqunada ----- Original Message ---- From: cyril pernet <[log in to unmask]> To: Shaquanda Jones <[log in to unmask]>; SPM <[log in to unmask]> Sent: Monday, November 5, 2007 6:20:58 AM Subject: Re: [SPM] Is it appropriate to smooth like this? Hi Shaquanda > I have heard that when you have a highly non-isotropic scan volume that it is appropriate to use a non-isotropic smoothing kernel. Is this true? > well I don't know if one can say it is true or not, but spatial smoothing will render your data data more normally distributed which is always good when you want to do some stats .. anyway I have no mathematical/statistical explanations here but the usual thing to do is to smooth 1 to 1.5 times the voxel size for individual data or about 3 times for group analyses, i.e. if you normalize at 2x2x2 for a group analysis, then a 6x6x6 FWHM (or higher) will do - now say you want to do some individual analyses then for e.g. a non-isotropic 3x3x5 voxel size, a 4.5x4.5x7.5 FWHM should be ok .. hope this helps cyril __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com