Susana,
Let p be the parameter vector of the GLM. Then:
a + b = Ap + Bp = (A + B)p = Cp = c.
Eric
Quoting Susana Santos <[log in to unmask]>:
> Dear All,
>
> I am studying the correlations between some brain regions. In
> order to do so, I am looking at the
> actual activation values in each region (for each subject) and
> then computing correlations between
> those values.
>
> I defined several contrasts and performed some additions with
> those contrasts. So, let's say I have
> the following contrasts:
>
> A = [1 0 0 0]
> B = [0 1 0 0]
>
> C = A+B
>
> So, C = [1 1 0 0]
>
> My question is the following: How is this "addition" of contrasts
> translated in terms of activation
> values? In other words: For contrast A, I observe value "a" in a
> given voxel (or ROI), for contrast B, I
> observe value "b", and for contrast C, I observe value "c". What
> is the mathematical relation
> between these 3 values? That is, what is the function f such that
> f(a,b)=c ?
>
> Thanks so much in advance for your help,
> Susana
>
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