[pymvpa] Cross-participant MVPA and controlling for traits of no interest

Cameron Craddock cameron.craddock at vt.edu
Tue Jul 12 18:50:31 UTC 2011

Hello John,

I have given this alot of thought in the past, and there are a few things
that might be worth trying:

1. When you say that the behavioral trait is not the same "type" as the
features, do you mean that it is not ordinal? If it is ordinal, then I don't
see any problem with adding it as a feature. Indeed this is how a lot of
data fusion algorithms work. You should be careful that the variance of the
behavioral score matches the variance of the other features. I.E. you should
z-score it as well as the features. This will ensure that the resulting
feature weights are comparable.

2. You could regress out the behavior score from your feature space. Fit a
glm to each voxel with the behavioral score as the regressor of interest,
and then perform the MVPA analysis on the residuals.

3. You could perform a MVPA regression to the behavioral score, perform a
feature selection to find the features most predictive of the behavioral
score, and then remove those features from the for the A vs. B

4. How predictive is the behavioral trait of the group membership? Can you
just threshold the behavioral score to ascertain group membership? If so
then you could perform a MVPA regression to the behavioral score, apply a
threshold to the prediction output, and see if this performs better to
classify group membership than a classifier trained using class membership
as the labels. I think that this is a pretty interesting idea.

Just a few thoughts.


Hi Jo -

Thanks for your response. The features are structural data, so yes, they are
voxel values.
It just so happens that a behavioral trait is also predictive of whether or
not participants are in Group A or Group B. Since the behavioral trait is
not of the same "type" as the features, it seems incorrect to simply add it
to the feature space. Still, though, I would like to "control" for the
predictability of that trait in the MVPA.
Does that make more sense?

R. Cameron Craddock, PhD
Postdoctoral Fellow
Virginia Tech Carilion Research Institute
Roanoke VA

cameron.craddock at vt.edu

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.alioth.debian.org/pipermail/pkg-exppsy-pymvpa/attachments/20110712/635711a3/attachment.html>

More information about the Pkg-ExpPsy-PyMVPA mailing list