For clarification....

Isotropic smoothness is the state of equal x-, y- and z-FWHM smoothness.  Non-isotropic smoothness is never a problem (SPM has never assumed isotropic smoothness).

Non-stationary smoothness is spatially varying FWHM smoothness.  SPM's cluster size inference assumes stationary smoothness; dealing with nonstationarity requires the NS toolbox (directly or via the VBM toolbox).


On Thu, Jun 19, 2008 at 1:57 PM, Simone Reinders <[log in to unmask]> wrote:
Hi Austin,

Isn't the non-isotropic smoothness related to the smoothness of the
statistical inference situation, i.e. the resels?


On Mon, Jun 9, 2008 at 10:04 PM, Austin Woolard
<[log in to unmask]> wrote:
> Is it necessary to correct for non-isotropic smoothness when one has
> isotropic voxel sizes during the first-level analysis in SPM5?
> Any relevant information would be very helpful.  Thanks!

Dr. A.A.T. Simone Reinders, MSc PhD
King's College London
Institute of Psychiatry (IoP)
Box P063, De Crespigny Park
London SE5 8AF
United Kingdom

Thomas Nichols, PhD
Director, Modelling & Genetics
GlaxoSmithKline Clinical Imaging Centre

Senior Research Fellow
Oxford University FMRIB Centre