Dear SPM:
I have noticed a curious issue about F contrasts which most likely
points out my ignorance of them but I have some questions.
F contrasts do not seem to be set up the same way as T-contrasts and
I don't understand the difference. For example if I had 1 subject
with 2 conditions (fmri data) a typical T-contrast to look at the
differences would be 1 -1. All contrast weights are entered on a
single line.
I've taken a look at the F contrast for all effects and it is set up
as a multiline contrast
1 0
0 1
and not as 1 1. Why is this?
So if I wanted to look at the F contrast of 2 conditions (cond 1 -
cond 2) modeled as an HRF+time deriv would I set it up as follows
1 0 0 0
0 1 0 0
0 0 -1 0
0 0 0 -1
Are T contrasts ever set up as multiline or alternatively are
F-contrasts ever set up as single lines. Could you please explain
these various alternatives and their implications.
Thanks,
Darren
Darren R. Gitelman, M.D.
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