Hi,
Can anyone tell me (or direct me to a good reference on) how SPM2
builds a design matrix in an fMRI experiment where there are two or
more continuous parameters assigned to a single condition? It seems
to create 2 (identically named) columns in the design matrix, the
first of which represents the first of the parameters, but it is not
clear to me what the second column is. It's not just the second
parameter... is it the interaction of the two parameters? How does
one go about entering two parameters for a single condition as
independent terms in the GLM model? Would one ever add the same
condition a second time and assign one parameter to each condition?
For example, in our experiment the subject separately gives two
ratings ("score1" and "score2") in response to stimuli, and we would
like to examine the parametric effects of each on brain activation in
a single model.
SPM.Sess(1).U(1).name = {'stimulusperiod'};
SPM.Sess(1).U(1).ons = stimulusons;
SPM.Sess(1).U(1).dur = stimulusdur;
SPM.Sess(1).U(1).P(1).name = 'score1';
SPM.Sess(1).U(1).P(1).P = score1data;
SPM.Sess(1).U(1).P(1).h = 1;
SPM.Sess(1).U(1).P(2).name = 'score2';
SPM.Sess(1).U(1).P(2).P = score2data;
SPM.Sess(1).U(1).P(2).h = 1;
SPM.Sess(1).U(2).name = {'ratingperiod'};
SPM.Sess(1).U(2).ons = ratingons;
SPM.Sess(1).U(2).dur = ratingdur;
etc.
SPM = spm_fmri_spm_ui(SPM);
SPM = spm_spm(SPM);
Thanks in advance.
Best, Andrew
Andrew J. Gerber, MD, PhD
Columbia University/NYSPI
Division of Child and Adolescent Psychiatry
Email: [log in to unmask]
Phone: (212) 543-5104; Fax: (212) 543-0522
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