Thanks Steve! I'll proceed along that line then.
Best regards
Cornelius
On Sat, Sep 4, 2010 at 10:58 AM, Stephen Smith <[log in to unmask]> wrote:
> Hi
> On 3 Sep 2010, at 17:07, Cornelius Werner wrote:
>
> Hello list,
>
> I've been following the discussion on conjunction analyses for a while, but
> here is something I am stuck with.
> We conducted a 3x2-factorial design with six conditions A1, A2, B1, B2, C1
> and C2. Our hypothesis is that there are common activations in a certain
> anatomical ROI due to A2>A1 AND B2>B1, but NOT C2>C1. If we constructed a
> linear contrast with
>
> A1 A2 B1 B2 C1 C2
> -1 1 -1 1 0 0
>
> this would simply pick up voxels responsive to any of -A1, -B1, A2 or B2,
> right? Plotting betas to show the desired pattern would probably qualify as
> "circular analysis", wouldn't it?
> So, is there any way of showing (-A1 +A2) AND (-B1 +B2) NOT (-C1 +C2)? Right
> now, I would go for a "conjunction overlay" approach by creating a mask from
> (-A1 +A2) and masking the other two contrasts with it, and see if anything
> survives within that mask. Are there any suggestions with more elegance than
> that?
>
> yes that sounds reasonable - though of course keep in mind wrt the "NOT"
> that failure to show significance (in C2-C1) is not statistically the same
> as saying that there was no activation (because you haven't defined an
> alternate hypothesis, but just done a null hypothesis test).
> Cheers.
>
>
>
> Best regards and thanks for any help
> Cornelius Werner
>
>
> ---------------------------------------------------------------------------
> Stephen M. Smith, Professor of Biomedical Engineering
> Associate Director, Oxford University FMRIB Centre
>
> FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
> +44 (0) 1865 222726 (fax 222717)
> [log in to unmask] http://www.fmrib.ox.ac.uk/~steve
> ---------------------------------------------------------------------------
>
>
--
Dr. med. Cornelius J. Werner
Department of Neurology
RWTH Aachen University
Pauwelsstr. 30
52074 Aachen
Germany
Institute of Neuroscience and Medicine
MR Physics - INM4
Research Centre Juelich
52425 Juelich
Germany
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