this is just the kind of newbie question that might go unanswered (:*}),
so even though I am a newbie myself, I will try to help. Any of you
gurus, please correct my mistakes.
Kerrie
>From: Ryan Dobbs <[log in to unmask]>
>Reply-To: Ryan Dobbs <[log in to unmask]>
>To: [log in to unmask]
>Subject: [SPM] wfu_pickatlas & FWE
>Date: Fri, 4 Aug 2006 16:37:13 +0100
>
>Yesterday I was informed not to use FWE when using wfu_pickatlas becasue
>it already performs a SVC. However, I had a couple questions for
>clarification:
>
>1. Can someone explain the rationale behind not using FWE and SVC. I'm
>pretty sure I understand why, but my boss said "that's how we've always
>done it," and is giving me a hard time about the info I was given.
FWE corrects the p-values for situations where large numbers of comparisons
are
made, as is the case when every voxel in a large image volume is tested for
significance. In the case where you are sampling a subregion, the number of
comparisons are fewer (by orders of magnitude) and the correction applied by
FWE is overly strict. the SVC (small volume correction) is a correction to
estimates
that can be applied in the case of sampling subregions, and is more
appropriate to
the WFU Pickatlas situation.
For a better explanation of why you need to make corrections in the first
place,
you'll need to do some reading . Try the book chapters on the SPM web
site.
>
>2. If i don't use FWE with wfu_pickatlas, do i choose none @ .001?
>
I believe this is correct, any comments from others?
>3. How do I create a mask using wfu_pickatlas? I've just been doing it
>manually, and no one here seems to be able to help me. I want one for
>[frontal - 9_44_45_46_47], 21_22_39, 44_45_47, 9_46, 9_44_45_46_47, etc.
>I was told to use the toolbox to create one, but I have no idea what i'm
>doing. Is this explained in the user's guide?
>
Lots of this is explained in the users guide, but basically you select
regions (that may
be predefined in the pickatlas) to include in the mask that you are
building, and this
mask is then used to sample the image. You can concatenate multiple regions
easily.
I am more interested in creating my own custom atlases/masks, and I noted in
the
manual that all atlases are created from ANA7.5 image formats, so
conceivabling a
segmentation program could be used to created very specialized masks, which
would
be incorporated into a custom atlas.
Hope this helps.
>Thanks
>Ryan
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