Dear SPM experts,
I am writing to seek a small favour, your opinion on the following.
The question is about orthogonality of contrasts when looking a group
by task interaction effects in a second level analysis.
Suppose that you have a simple ANOVA with two columns one for a
control group and one for a patients group
Contrast images here represent signal changes of a task minus baseline
comparison (say reading miinus fixation)
My recollection is that the two contrasts
1 -1 the group x task interaction effects
and
1 1 the main effect of activation across the two groups
are orthogonal and therefore the nominal significance in the first SPM
( the 1 -1 ) should be the square
for the voxels that are also significant for the 1 1 contrast
(voxel identified by inclusive masking)
Is this correct?
I would much appreciate your comment on this, as the various answers
I got so far were not clear.
Best wishes
Laura Danelli
--
Laura Danelli - PhD student
Dipartimento di Psicologia - Universitą di Milano-Bicocca
Room 3126 - Building U6
Piazza dell'Ateneo Nuovo 1
20126, Milano, Italy
Tel: +39 02 64483776
Fax: +39 02 64483706
E-mail: [log in to unmask]
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