[log in to unmask] wrote:
> Dear Will,
> Thanks so much for the detail! Very helpful.
> Suppose I just want to do a conjunction analysis for the two
> conditions first, I can either use full factorial design or two
> sample design, correct?
Yes, that's right.
May I select paired two sample design, as the
> two conditions are perfomed for the same group subjects?
Actually, that's a good point. If your effects are all-within subject
then you should also include subject effects for your 3-way conjunction.
To do this have a look at p.254 (section 31,3,1) of the SPM manual (you
will have 1 factor with 3 levels, and enter the data subject by
subject - the conditions vector for each subject will be [1 2 3], you
won't need any global normalisation - this is only for PET)
> If I want to see if there is a interaction among tasks(A,B,C) *
> hands(uncross,crossed)* compatibility(compatible, incompatible)? what
> I should do? Thanks!
A 3-way interaction at the 2nd level !
Perhaps the easiest way is, for each subject, create the two-way
interaction contrast - the interaction between hands and compatibility.
This will be 1 -1 -1 1 over the uncross,crossed,compatible,incompatible
columns of your first level design.
Then you have one con image per subject per task.
At the second level create a one-way ANOVA with 3 levels (using full
factorial as before). You don't need subject effects in your 2nd level
design here because the data you are taking up are differences (ie.
subject effects already removed). This will create
a design matrix with 3 columns A, B, C.
To test for an interaction among your two-way interactions ie. a
3-way interaction, use the F-contrast [1 -1 0; 0 1 -1].
> Regards, Chunhong
William D. Penny
Wellcome Trust Centre for Neuroimaging
University College London
12 Queen Square
London WC1N 3BG
Tel: 020 7833 7475
FAX: 020 7813 1420
Email: [log in to unmask]