Hi - the natural extension for a linear trend would be:
3D + C -B -3A (so that the gaps between each jump are constant).
Cheers.
On 12 Oct 2008, at 12:45, Benny Liberg wrote:
> Dear list,
>
> In my experiment I have 1 condition of interest. Each subject did 4
> runs
> where the level of task difficulty was linearly increased in 4
> steps. In my
> 2nd level analysis I have done 4 group T-test set up like this for
> each
> individual:
>
> Condition EV1 EV2 EV3 EV4
>
> A 1 1 1 1
> B -1 0 0 1
> C 0 -1 0 1
> D 0 0 -1 1
>
> A = a+b+c
> B = -a
> C = -b
> D = -c
>
> D-A = (-c)-(a+b+c) = -a -b -2c
> C-A = (-b)-(a+b+c) = -a -2b -c
> B-A = (-a)-(a+b+c) = -2a -b -c
>
> Contrasts EV1 EV2 EV3 EV4
>
> D-A -1 -1 -2 0
> C-A -1 -2 -1 0
> B-A -2 -1 -1 0
>
> Is there any way to investigate linear effects at this level to find
> those
> voxels that show a linear increase from A->D? If yes, how is this
> contrast
> set up? Any help is much appreciated.
>
> Cheers,
> Benny
>
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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)
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