Dear all, In group analysis, how should I determine which value to use for the Gaussian fwhm smoothing kernel? Is there a recommended number? Thanks, Sasha
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There's no real good answer to this, either in the volume or the surface. We usually go from 5-20mm. Some considerations are:
1. Make fwhm = size of your activation. 2. More smoothing can sometimes compensate for misregistration 3. Smoothing does affect multiple comparisons.
doug
Sasha Wolosin wrote:
Dear all, In group analysis, how should I determine which value to use for the Gaussian fwhm smoothing kernel? Is there a recommended number? Thanks, Sasha
Disclaimer: The materials in this e-mail are private and may contain Protected Health Information. Please note that e-mail is not necessarily confidential or secure. Your use of e-mail constitutes your acknowledgment of these confidentiality and security limitations. If you are not the intended recipient, be advised that any unauthorized use, disclosure, copying, distribution, or the taking of any action in reliance on the contents of this information is strictly prohibited. If you have received this e-mail in error, please immediately notify the sender via telephone or return e-mail. _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
Hi Sasha,
it depends on how many subjects you have in your study (more subjects, less smoothing required), and how anatomically localized you believe your effects should be (more localized less smoothing). Note that in general you don't pay nearly as steep a price for extremely large smoothing kernels on the surface as you do in the volume, since the surface-based kernel never extends into bone/air/white matter etc. We've used a wide range of values, anwhere from 5 to 30mm fwhm.
cheers, Bruce
On Thu, 25 May 2006, Sasha Wolosin wrote:
Dear all, In group analysis, how should I determine which value to use for the Gaussian fwhm smoothing kernel? Is there a recommended number? Thanks, Sasha
Disclaimer: The materials in this e-mail are private and may contain Protected Health Information. Please note that e-mail is not necessarily confidential or secure. Your use of e-mail constitutes your acknowledgment of these confidentiality and security limitations. If you are not the intended recipient, be advised that any unauthorized use, disclosure, copying, distribution, or the taking of any action in reliance on the contents of this information is strictly prohibited. If you have received this e-mail in error, please immediately notify the sender via telephone or return e-mail. _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
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Bruce Fischl -
Doug Greve -
Sasha Wolosin