Psychologists who work with functional magnetic resonance imaging
(fMRI) often wish to make statements about the functional brain
behavior of a group of subjects. In order to do this, it is necessary
to create a so-called "group map," which combines the activation of
the individual subject brains in a (statistically) sensible fashion.
Creating these maps involves defining a test statistic at each voxel
of the brain that takes into account the level of activity displayed
by every subject at that voxel, and thresholding to reveal areas of
group activation. In this talk I show how, using some simple (and
some not so simple) techniques for combining information already in
use in the statistics literature, it is possible to generate group
maps of the brain from the fMRI data of individuals. I also describe
a "leave one out" approach for assessing the sensitivity of combining
techniques to the effects of individual subjects. Finally, I will
argue that the desiderata for a good combining technique in fMRI can
be different from those that are generally assumed in other data
analysis contexts.