Dear colleagues,
I have a question about my event-related design. For the first time,
I am using an implicit baseline, where I do not model the cross-hairs
(in the beginning and end of the session and between events). I have
two conditions and two runs. I am using the HRF and the two derivatives.
When I set up the model, everything looks fine. When I look at the
design matrix after estimating the model, however, I notice that the
regressors are non-zero where they should be zero. For example, no
presentations of condition FIRST are made after the first half of the
first session. However, the regressor for the rest of the session for
this task is non-zero. This is seen as slight white shading for
regressors #1 for the second half of the first session (circled area
on the attached picture).
Can anybody explain this? Does it have anything to do with the fact
that I am using an implicit baseline and do not model parts of the
sessions? This has never happened to me before.
Thank you very much,
Martin
Martin Zalesak, M.Sc.
PhD Candidate in Medical Engineering
Harvard-MIT Division of Health Sciences and Technology
Admissions Building, Rm. # 347
McLean Hospital
115 Mill St.
Belmont, MA 02478
Phone: (617) 855-2229
Fax: (617) 855-2895
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