Dear Alex,
> Thank for you help. I have done what you suggested, and now, I'm stuck at the
> contrast stage.
>
> > and use F-contrasts to test for mean effect and differences in the
> > epoch-related responses.
>
>
> I have four conditions and the design matrix now has 8 columns, 2 for each
> condition. I'm not used to looking at F maps. Usually, if I was comparing
> t-maps, I would enter a contrast 1 -1 0 0 if I wanted to compare condition A
> with B. Do I now enter:
> 1 1 -1 -1 0 0 0 0
> or do I look at the individual activations
> 1 1 0 0 0 0 0 0 and
> 0 0 1 1 0 0 0 0
> and then use making to look at commonalities/differences?
First use the F-contrasts computed by default in the results section -
contrast manger, under F-contrasts. These will give you the condition
specific F-contrasts. For example the responses due to condition 1
should look like:
1 0 0 0 0 0 0 0
0 1 0 0 0 0 0 0
To look for the differences between condition 1 and 2 use something like:
1 0 -1 0 0 0 0 0
0 1 0 -1 0 0 0 0
If you have used 'mean and decay' than you can also try the
conventional T-contrasts looking for differential respones in terms of
mean or decay. For the 'mean' it is simply:
1 0 -1 0 0 0 0 0
An F-contrast can be though of as a collection of T-contrasts, that you
wish to test jointly.
I hope this helps - Karl
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