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Stefanie Lis,

Central Institute of Mental Health

Department of Psychosomatic Medicine and Psychotherapy,

Medical Faculty Mannheim, University of Heidelberg,

Head of research unit 'Experimental Psychology'

J 5

D-68159 Mannheim

Germany

phone: +49-621-1703-4424

fax: +49-621-1703-4405

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Von: SPM (Statistical Parametric Mapping) im Auftrag von Enzo Tagliazucchi
Gesendet: Mo 26.03.2012 07:52
An: [log in to unmask]
Betreff: Re: [SPM] smoothing

Hi,

essentially this depends on the anatomical size of the expected effect. Using a 8 mm FWHM kernel will make difficult to detect small activations smaller than the FWHM since the response can be effectively killed by the blurring. On the other hand if you use very small FWHM your data may not be smooth enough to fulfill the assumptions required by random gaussian field theory when you correct for multiple comparisons. The standard FWHM is most likely to reflect a balance between these two extremes.

Bw,
Enzo