Dear all,
I would like to do a dual-regression analysis on resting state data, but am unsure about the best way to define my contrast matrix.
The study has 15 subjects. Each came in on two seperate days, one where they performed a learning task, and one where they performed a control task. On each day, they had a resting state scan before and after the task. So I have 60 resting state scans, 4 per subject.
I am interested in possible changes in the resting state networks induced by the learning task (not the control task), so I would like to look at the interaction between time (pre and post resting session) and condition (experimental task versus control task).
However, I am usure about the way I should define my design and contrasts.
My design matrix looks like this (without scientific notation for easier reading):
The columns are subject, condition (0 is control, 1 is experimental), time (0 is pre, 1 is post), counterbalancing(0 is control first)
/NumWaves 4
/NumPoints 60
/PPheights 15 1 1 1 1
/Matrix
1 0 0 0
1 0 1 0
1 1 0 0
1 1 1 0
2 0 0 1
2 0 1 1
2 1 0 1
2 1 1 1
3 0 0 0
3 0 1 0
3 1 0 0
3 1 1 0
4 0 0 1
4 0 1 1
4 1 0 1
4 1 1 1
5 0 0 1
5 0 1 1
5 1 0 1
5 1 1 1
6 0 0 1
6 0 1 1
6 1 0 1
6 1 1 1
7 0 0 0
7 0 1 0
7 1 0 0
7 1 1 0
8 0 0 0
8 0 1 0
8 1 0 0
8 1 1 0
9 0 0 1
9 0 1 1
9 1 0 1
9 1 1 1
10 0 0 1
10 0 1 1
10 1 0 1
10 1 1 1
11 0 0 0
11 0 1 0
11 1 0 0
11 1 1 0
12 0 0 0
12 0 1 0
12 1 0 0
12 1 1 0
13 0 0 0
13 0 1 0
13 1 0 0
13 1 1 0
14 0 0 1
14 0 1 1
14 1 0 1
14 1 1 1
15 0 0 0
15 0 1 0
15 1 0 0
15 1 1 0
On the basis of this structure I haven't managed to readily define sensible contrasts.
Because of the 'long' format of the design matrix, I can't seem to be able to contrast between the levels of the variables.
Initially I thought to add columns to my design matrix (a column per level of each variable), but that renders the design matrix rank deficient (right?).
On the basis of the above design matrix, would it be correct to say (for example)
Main effect of time: t = [0 0 1 0]
Interaction (post_experimental - pre_experimental) - (post_control - pre_control): t = [0 1 1 0] ??
It would be great if anyone could tell me if I've defined my design matrix correctly, and how I should define the contrasts.
Any help would be very much appreciated!
Elise
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