Hi,hengyi,
I think the baseline beta you should use here is the session regressor weight(SPM removes the mean signal within a session by using a session regressor which is just 1s in the scans for this session and zeros elsewhere),then divide the task beta value by the baseline beta value.
What do you mean about define a contrast by 'task-baseline', that will give you a T_map not betas.
>hi, Stephen,
>
>Thanks for your comments.
>
>If my experiment was a simple block design, only included one session that was consisted of one baseline condition and one task condition, and my contrast was defined as the task-baseline. Thus the grand mean scaling should equal the local mean value, right? Then can i say that beta value represent the percent signal change associated with the task in my paper?
>
>
>hengyi
>----------------------------
Zhang Peng
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2005-03-29
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