Thanks so much, Helmut. Most appreciated!
Warm regards,
Jeff
On Aug 17, 2015, at 9:56 AM, H. Nebl <[log in to unmask]> wrote:
> Dear Jeff,
>
> The order of the columns was changed with one of the SPM updates, but the principle for setting up contrasts is still the same,
>
> for the main effect time go with
> [zeros(1,2) 1 -1 0 .5 -.5 0 .5 -.5 0 zeros(1,44)
> zeros(1,2) 0 1 -1 0 .5 -.5 0 .5 -.5 zeros(1,44)]
>
> and for the interaction group x time
> [zeros(1,2) zeros(1,3) 1 -1 0 -1 1 0 zeros(1,44)
> zeros(1,2) zeros(1,3) 0 1 -1 0 -1 1 zeros(1,44)]
>
> (please double-check yourself). For main effect group you should create an average s8wp1 file for your different subjects = (image from time point 1 + time point 2 + time point 3)/3 and forward this into a two-sample t-test to test for differences between group 1 and 2 to have the correct error term for that contrast. Donald McLaren has written quite a lot on that issue on the list.
>
> To make sure you're looking at the same selection of voxels in the two-sample t-test I'd go with the mask.nii obtained from the Flexible factorial and specify this as an explicit mask for the two-sample t-test instead of the threshold masking \ absolute threshold.
>
> Best
>
> Helmut
|