Dear Goldie,
The contrast you propose is fine, provided you set up your regressors
correctly in the design matrix.
If your first regressor is the task regressor, and the second the
control regressor, the contrast [1 -1] tests for greater activation
during task than control. The contrast [-1 1] then tests for greater
activation during control than during task.
All the best,
Floris
>Hello!
>I am working on an fMRI project where we had the subjects alternate between
>two tasks in order to ascertain whether a certain part of the brain was
>activated during one particular task. I have a rather fundamental question.
>I am new to SPM, and still trying to understand how best to approach my
>data set.
>If my test is run as
>task-control-task-control-task-control,
>is it correct to use the contrast {1 -1}? If I am correct, then this will
>show areas which are more active in task than in control. Is it true then
>that {-1 1} will show areas which are less active in task than in control,
>or, show more activity for the control than for the task in question?
>
>
--
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Floris de Lange
FC Donders Centre for cognitive neuroimaging
P.O.Box 9101
6500 HB Nijmegen, Netherlands
e-mail: [log in to unmask]
phone: (+31)-024 3610887
web: www.fcdonders.kun.nl
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