@M: Thanks for the quick & helpful answer! But I'm not sure about two further issues:
1. Yes - the fixation periods should serve as a baseline. Would it be useful to incorporate some "empty trials" just showing the fixation cross with the same length as the experimental trials?
2. Must the randomly inserted jitter periods start with the new image acquisition (according to the TR, that means do I have to sync the start of the jitter periods with the cycle of the TR)?
Thanks in advance & kind regards
ben
Hi B,
We've used MTS and DMTS procedures for a few experiments and what you
propose sounds fine. Although the upper limit of the fixation period seems
pretty lengthy by my standards, it too is fine. You could probably be fine
with a 500-6000 range, unless this period will serve as some sort of
baseline.
Cheers,
M
===============================================
Michael Schlund, Ph.D.,
Assistant Professor of Psychiatry, Johns Hopkins University, School of
Medicine.
Faculty, Kennedy Krieger Institute, Department of Behavioral Psychology;
Director, Neurobehavioral Imaging Laboratory.
Research Scientist, Department of Behavior Analysis, University of North
Texas.
Adjunct Assistant Professor of Psychiatry, University of Pittsburgh,
School of Medicine.
> Dear SPMers,
>
> I want to program a delayed-matching-to sample (dmts) task for an
> event-related fMRI study. I want to jitter the onsets of the single task
> trials. Each dmts trial lasts 7000ms. To temporally jitter between trials
> I am planning to randomly insert fixation periods lasting between
> 500-7500ms (in 500ms steps) between the dmts trials. The TR of the
> MRI-sequence I want to use is 2500ms.
>
> My questions:
>
> 1. Is it valid to simply insert the fixation periods between the trials or
> do I have to consider the TR of the sequence? Or is the jittering only
> valid when I insert the fixation periods when the acquisition of the new
> image starts?
>
> 2. Are the the jitter periods of an appropriate lengths?
>
> Thanks in advance & kind regards
> Ben
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