Thanks Jesper
I thought that susan wanted half width at half maximum = FWHM/2. I
will make sure to pass FWHM/2.355 then.
Best
Enrico
On 26 Oct 2010, at 13:08, Jesper Andersson <[log in to unmask]>
wrote:
> Dear Enrico,
>
>> I have been checking the standard preprocessing scripts (prestats)
>> and
>> noticed at line 5274 of file featlib.tcl
>>
>> set smoothsigma [ expr $fmri(smooth) / 2.355 ]
>>
>> Could you briefly explain where the 2.355 comes from?
>
> it is simply a conversion factor between FWHM and sigma, reflecting
> that the user is asked for the smoothness in FWHM whereas the script
> that does the actual smoothing expects it in sigma.
>
>> That happens before registration to standard template: does it mean
>> that if it was happening after registration to template then: set
>> smoothsigma [ expr $fmri(smooth) / 1 ] is valid?
>
> Nope.
>
> Good luck Jesper
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