Dear all,
I'm playing around with modeling the 'true' hemodynamic response for
individual subjects (after stroke), using FIR. This works fine for main
effects, when I give the correct weights to my time bins. However, I'm not
sure how to model contrasts subtracting one condition from another. Should I
simply give the negative weights to the condition I am subtracting?
Say, I have 10 time bins, which I can give a certain weight to resemble the
hrf that I have measured with a different method:
0.25 0.4 0.6 0.8 0.9 0.85 0.7 0.5 0.2 -0.1 (I'm just making up the numbers)
And my conditions are A and B, in an FIR model with 10 time bins. Would my
t-contrast subtracting B from A be:
0.25 0.4 0.6 0.8 0.9 0.85 0.7 0.5 0.2 -0.1 -0.25 -0.4 -0.6 -0.8 -0.9 -0.85
-0.7 -0.5 -0.2 0.1
?
This way, the contrast adds up to zero, as it should, but it still seems odd
to me - it seems to entail a very specific hypothesis about how voxels
'respond' to condition B ...
Any comments, or references to helpful FIR work, are welcome!
thanks,
Dirk
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Dr. Dirk-Bart den Ouden, Northwestern University
Aphasia & Neurolinguistics Research Laboratory
Dept. of Communication Sciences & Disorders
2240 Campus Drive, Evanston IL 60208-3066
Phone (lab): 1-847-467-7591
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