Hello,
I am attempting to determine effective smoothing on my SPM contrast images in order to apply appropriate clustering thresholds. In the results panel, when I load a contrast, I notice that at the bottom, my original FWHM smoothing kernal applied is shown in the xyz direction, and is preceded by what I assume is that kernal with effective smoothing applied. e.g. In my data a 6mm smoothing kernal was applied in the xyz direction, and my results show roughly a FWHM kernal of 12 applied in the xyz direction, my understanding is that this is with effective smoothing incorporated. I attempted to use a function in AFNI to confirm the smoothing in the xyz direction(known as 3dFWHMx), however it gave me very different outputs than that 12mm in the xyz direction, in fact it gave a reduced smoothing(8 6 4 ). This may be an issue of trying to apply a function from one software to data of another(indeed a I had to convert the SPM images into tlrc space). I'm wondering, what tool within SPM do SPM users commonly use to determine their appropriate cluster thresholds to set to survive correction for multiple comparisons? I appreciate any help, thank you!
Sam DeWitt
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