Instead of using the jitter technique, you can use the stagger
technique. This is where the TR and the trial timing are not even
multiples of each other (e.g., 2 second trials and 2.1 second TR),
with the result that the data acquisition corresponds to different
points of the hemodynamic response on different trials. This has the
same effect of enhancing the hrf sampling but in a way that is
invisible to the subject and hence does not affect the psychological
processes. The citation for this technique is (although it only
describes it in passing):
Josephs, O., Turner, R., & Friston, K. J. (1997). Event-related fMRI.
Human Brain Mapping, 5, 243-248.
Cheers!
Joe
On May 11, 2007, at 2:43 AM, Federico Tubaldi wrote:
> Dear Experts,
>
> First of all exscuse me if this problem does not concern directly
> SPM infact
> I have a question about the possibility to use jitter in priming
> paradigm.
> I am interest in activation related to prime presentaion (event 1,
> duration=3 sec.) rather than activation related to task execution
> on target
> presentation (event 2). So I think to insert jitter between prime
> presentation and task execution/target presentation to improve hrf
> sampling
> related to prime presentation. But I suppose that priming effect on
> task
> execution depend on prime-target time interval (e.g., 100 ms) so
> its change
> probably modifies priming effect.
> Do you have some advice about the possibility to use jitter between
> prime
> presentation and task execution/target presentation?
> Could you suggest me some reference?
>
> Many thanks in advance.
>
> Federico.
>
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Joseph Dien
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