Dear SPMers,
I have run an fMRI parametric working memory task. Now I have some questions regarding the parametric analysis.
The task:
4 conditions of working memory load (participants have to maintain 1/2/3/4 items)
1 baseline condition (during which participants view a fixation cross)
My questions:
1. Modeling the parametric response:
On the first level I have modeled the 4 load conditions as 1 condition with a parametric modulation (entering a vector with 1,2,3,4 according to the onset times of the 4 conditions)
As a result I get a design with:
First row: onset times
Second row: parametric modulation
(please correct me if I’m wrong)
Does the t-contrast 1 1 return the parametric contrast (the load-dependent working memory network)? If not: what would the appropriate contrast be?
2. Would it be reasonable to include the baseline in this design?
3. Alternatively I used a different first-level analysis:
I entered 5 conditions: baseline / load1 / load2 / load3 / load4 and their onsets
No parametric modulation.
Then entered the t-contrast:
-6 (baseline) 0 (load1) 1 (load2) 2 (load3) 3 (load4)
Would this approach display the load-dependent working memory network?
If it does: which approach (1 or 3) should be preferred?
Thanks in advance & kind regards,
Ben
_________________________
Dr. rer. nat. Benjamin Becker
Dipl.-Psych.
NEMO Research Group
Department of Psychiatry
University of Bonn
Sigmund-Freud-Str. 25
53105 Bonn
Germany
Tel.: +49 (0)228 287 11151
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