Nathan,
>
> To Whom it May Concern,
>
> I have a question regarding the use of contrasts when generating
> subtraction images. Basically, we have mutiple subjects with
> different conditions. Here is the question:
>
> - Say for subject 1 we have two scans: A,B
> - In SPM's selection window I select the order: A=1, B=2 (A-B)
> - Then I select two contrasts, the first contrast being "1 -1"
> and the second being "-1 1"
> - Then does contrast 1 correspond to:
>
> 1. pixels significantly higher in condition A vs. B
> 2. pixels significantly lower in condition A vs. B
> 3. pixels significantly higher in condition B vs. A
> 4. pixels significantly lower in condition B vs. A
If you mean "the voxels above threshold for contrast 1 correspond to:"
then the answer is both 1 and 4 (also 2 and 3 equivalently
correspond to the voxels above threshold for contrast 2).
Sincerely,
Eric
Eric Zarahn
Columbia University
>
> Thank you very much for your time, and I look forward to hearing
> from you soon.
>
> Nathan White
> College of Medicine
> Department of Anesthesiology
> University of California, Irvine.
>
> =====
> Nathan S. White
> [log in to unmask]
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