Dear all,

I have some basic questions about a factorial analysis I have done with SPM8. I have little experience in dealing with Factorial Design, so please

forgive me if my question looks so naive. And thank you all in advance.

I have two groups of patients, 'Real' and 'Sham', according to the treatments they received. Each subject had a fMRI scanning before and after the

treatment. So, I did a 2*2 factorial design, factor I: Real(two levels) and factor II: Sham(two levels). I have attached a picture of the design matrix

and a picture of the SPM contrast manager which included 8 contrasts defined by default and the 9th contrast which was defined by myself.

My questions are:

1. Why there were different intensities of the four cells in the design matrix and what did that mean?

2. I didn't quite understand the difference between t-contrasts and f-contrasts.

I saw they were both constructed with 1 and -1, but SPM applied different kinds of figures to illustrate them.

Besides, I couldn't understand the definition of some contrast.

Such as 003{F}: 1 -1 1 -1 Main effect of sham, it was different from 002{F}: 1 1 -1 -1 Main effect of real.

The same question happened to the 006{T} and 007{T}.

3. Since I intended to find the difference between 'Real_2 - Real_1' and 'sham_2 - sham_1', I defined 009{T}:-1 1 1 -1, What would be the

difference if I defined a F-contrast with the same vector [-1 1 1 -1]?

Hope I have described my questions properly.

Best wishes!