Dear SPM:
I want to set up an fmri design which will basically just allow me to
remove a variety of covariates of no interest. Once these covariates
are removed from the data I will use the data in another way. Karl
answered a previous question about how to remove the covariates using
spm_regions. This question is one step before that.
What I want to know is how do I set up a design matrix so there are
basically no covariates of interest? spm97 allowed one to do this by
answering 0 to the covariates of interest question. I don't know how
to do this in spm99.
The following did not seem to work
I set up a design as follows.
There are 200 scans in the session taken at a TR of 3.
So # of trials or conditions= 1
SOA of trial 1 = 200
Onset of trial 1 = 0
Length of trial 1 = 200.
not stochastic, fixed onset.
I then enter a number of covariates which end up being my covariates
of no interest.
The resulting design matrix has all 0's as it's first column,
followed by the covariates [of no interest] followed by a mean vector
of all 1's.
I then looked at a series of F contrasts-
The first column of the design (all 0's) is not uniquely estimable so
I can't define a contrast as just 1. Likewise choosing columns for
the reduced design of either 1 or 2:112 doesn't give the right answer.
Any ideas?
darren
Darren R. Gitelman, M.D.
-------------------------------------------------------------------------
Cognitive Neurology and Alzheimer's Disease Center
E-mail: [log in to unmask] WWW: http://www.brain.nwu.edu
Voice: (312) 908-9023 Fax: (312) 908-8789
Northwestern Univ., 320 E. Superior St., Searle 11-470, Chicago, IL 60611
-------------------------------------------------------------------------
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
|