Cognitive Scientist
I am retired, but still doing research. Recently
I started collaborating with Howard Poizner, who works on Motor Control
Deficits in Parkinson's Disease. My interest in theory and modeling
complements his experimental approach in a
constructive way.
For example, the work that Elizabeth Torres and I have done has led to
a mathematical model that accounts for many aspects of normal 3D
reaching and grasping movements of a seven degree of freedom arm
model. Since some of these movements are disrupted in PD it
will be informative to see what components of the model have to be
altered to account for the behavior observed in PD. In particular it
would be interesting to see if the normal pattern of coarticulation of
translation and rotation is disrupted in PD. The model accounts for
this coarticulation by combining rotation and translation information
in a single cost function which is minimized. If it were disrupted this
might be accounted for by a failure to be able to integrate different
sources of sensory information. This model can also be used to
investigate many other factors that effect motor behavior.
In addition I am working on a number of demonstration models designed
to illustrate the effects of disruption of various basal ganglia
functions on motor behavior. One of these models is concerned with the
effects of the correlated firing in BG output that accompanies PD. It
could be the source of some PD symptoms. I am training a neural network
to move a simple arm model to targets specified by an uncorrelated
input format. When I add correlation to this input I expect to see
errors in the arm movements. It would be interesting to compare these
errors with those made in PD. In any event the model will clearly
illustrate that correlated inputs to a system that doesn't generally
receive them can disrupt movement. I hope to be able to construct a
whole series of models of this sort. The one I already did on
the different effects of visual target location and initial arm posture
errors on arm paths, although oversimplified, has been suggestive.
One of the most important aspects of our collaboration is our
continuing discussions about what role the BG plays on brain function.
These have been particularly stimulating and I have become very
interested in what the BG really does, something that is not at all
obvious.

