Dear list,
We are trying to specify a subject-specific HRF as a basis function at the
individual level of analysis. The 'subject-specific HRF' is an
independently collected and averaged timecourse of signal intensity in a
cluster in the motor cortex during a separate (motor) task.
It appears that this can easily be added as an option in spm_get_bf.m, by
adding a 'user specified hrf' option for the Cov variable around Line 91,
and inserting a condition to import a user-specified vector for bf,
instead the default SPM's hrf around Line 150, which is now:
[bf p] = spm_hrf(dt);
However, I was wondering, are there any properties that a Gamma
basis function has (and that a user-specified vector may not have)
that are used at some later stage of the statistical modelling and the
benefit of which would be lost in the case of a user-specified vector?
In other words, would it be better from the point of view of statistics
to change the bf variable to match the subject-specific response, or to
change the set of parameters p to match the subject-specific parameters?
Thanks in advance for any suggestions or opinions.
Best,
-k.
_____________________________________________________________________________
Kalina Christoff Email: [log in to unmask]
Office: Rm.478; (650) 725-0797
Department of Psychology Home: (650) 497-7170
Jordan Hall, Main Quad Fax: (650) 725-5699
Stanford, CA 94305-2130 http://www-psych.stanford.edu/~kalina/
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