I'm not positive, but I believe that my suggestion should match this two-step procedure. If you specify the mask as the first step of viewing the results, and then just threshold at p(FWE)=0.05, you should get volume-corrected results in one step.
In versions of SPM prior to 8 (I think) this wasn't an option, because you could only mask with other contrasts. But you can now select an image to reduce your search volume from the beginning.
-Mike
> -----Original Message-----
> From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]]
> On Behalf Of MRI More
> Sent: Thursday, September 01, 2016 9:41 AM
> To: [log in to unmask]
> Subject: Re: [SPM] initial threshold for small volume correction
>
> In case you want to perform SVC on peak level you should go this way:
> (1) Select your contrast, enter any threshold, be it corrected or uncorrected,
> this is irrelevant
> (2) Define your small volume
> (3) Look at the updated FWEp at the bottom up the results table, this is the
> critical T (or F) value for .05 FWE on peak level for the small volume
> (4) Re-load the contrast, choose "none" for "p value adjustment to control",
> enter the T (or F) value from (3)
> (5) Define your small volume like you did in (2)
>
> If you don't do so, then the SPM is not thresholded properly, as it would still
> reflect e.g. .001 uncorrected on peak level or any other value that you might
> have entered during (1). As a consequence, depending on whether the
> corresponding T (or F) value is smaller or larger than the one reflecting .05
> FWE for the small volume, you either miss voxels that would actually be sig.,
> or you include voxels that are in fact non-sig. Accordingly, the k in the table
> would be incorrect, and the table might be incomplete, as peaks being non-
> sig. based on the threshold from (1) but sig. based on the threshold in (4)
> would not show up.
>
> > btw, I found many articles did not describe the initial threshold they used in
> svc
> I wouldn't be surprised if many of the SVC were conducted incorrectly = with
> an incorrect threshold. In addition, if people really had a-priori regions they
> should in fact start with the SVC and only then look at the whole-brain results
> for the rest of the brain. However, in all of the papers I remember it's the
> opposite, that is after failing to detect sig. effects on whole-brain level (or
> finding some in a subset of "a-priori" regions only) they turn to SVC. This
> doesn't make sense; if I had several a-priori regions and assuming I want to
> rely on SVC then I would want to combine those into a single mask and then
> look at all of them based on the SVC threshold.
>
> Hope this helps
>
> Helmut
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