Dear list
I have been testing the worked example in chapter 29 of the spm
manual, which is a great example dataset for teaching! I have
however, been unable to reproduce the parabolic parametric response of
lag shown in figure 29.18. I noticed that the coordinate for the
response in figure 29.18: [-54, 21,48] is different from the
coordinate of the global maximum in the MIP on figure 21.17 which is
[-51, -25, 46]. This indicates that the 3D plot could be from a much
earlier version of the software :-) By plotting the "Contrast
estimates and 90% C.I. one can confirm that the slope of the quadratic
regressor is negative and significant corresponding to the parabola
seen in figure 21.18.
By changing line 569 of spm_graph
from:
q = [q spm_en(P).^i];
to:
q = [q (P).^i];
I am able to reproduce a response close to the one seen in figure
29.18 the manual. The results are in the attached, zipped, PS file
(the blurry designmatrices is a mac-only feature).
I am uncertain why spm_en is needed but it seems to me that the betas
are not scaled appropriately together P (the values of the parametric
modulation).
I hope this will be useful
Best
Torben
Torben Ellegaard Lund
Associate Professor, PhD
The Danish National Research Foundation's Center of Functionally
Integrative Neuroscience (CFIN)
Aarhus University
Aarhus University Hospital
Building 10G, 5th floor, room 31
Noerrebrogade 44
8000 Aarhus C
Denmark
Phone: +4589494380
Fax: +4589494400
http://www.cfin.au.dk
[log in to unmask]
|