I'm still struggling a little with understanding how contrasts need to be
specified in spm99... The timecourse does not always look like I expect it
to!
I have the following blocked fmri design:
control task control task control task
If a set it up as one condition and use the contrast [1] then I see areas
that are activated with respect to the control. The contrast [-1] reveals
areas that are deactivated with respect to control.
However, I'm interested in the task vs. control (activation) x time
interaction. So I specified the design as 3 conditions. I thought that I
could mask [1 1 1] (task activated wrt control) with [1 2 3] (increasing
trend over time) or [3 2 1] (decreasing trend over time). However, the [1 1
1] contrast appears to show regions that are both activated and deactivated
for task wrt control. Can anyone explain this?
thanks in advance,
Rachael
Rachael D. Seidler, PhD
University of Minnesota Dept of Neuroscience
and Brain Sciences Center (11B)
Veterans Affairs Medical Center
Minneapolis, MN 55417
Phone: 612 725-2000 x.1765
Fax: 612 725-2291
Email: [log in to unmask]
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