Neural Foundations of Vision 
In addition to its purely visual functions, the M 
stream provides signals that drive eye movements 
of pursuit, the slow^, smooth eye movements with 
which primates stabilize on the retina the image 
of a moving visual target. In collaboration with 
Stephen Lisberger (University of California, San 
Francisco) , we have studied several aspects of the 
relationship between visual and visuomotor pro- 
cesses. In a series of neurophysiological studies, 
we have explored the responses of MT neurons to 
the dynamic motion profiles used to characterize 
pursuit, and have documented the suitability of 
the motion-related signals in these neurons for 
the task of initiating pursuit. In psychophysical 
work, we have begun to explore the kinds of vi- 
sual signals that pass into the oculomotor system 
by examining the relationship between the de- 
tectability of particular visual patterns and the 
pursuit eye movements they elicit. 
Our overall ambition for these studies is to 
"turn the sensory-motor corner" and relate the 
particulars of visual processing to the higher 
mechanisms that produce voluntary motor com- 
mands. To this end, we are developing computa- 
tional models designed to explain the signal 
transformations that take place at a series of stages 
between the initial registration of the visual 
image and the formulation of the final oculomo- 
tor command. 
To analyze development, we study the vision 
of monkeys reared either with an artificial stra- 
bismus (deviation of one eye) or anisometropia 
(difference in the refractive state of the two 
eyes). Both of these manipulations lead to con- 
ditions resembling human amblyopia, a com- 
mon visual deficit of central nervous system ori- 
gin. In behavioral experiments, we learn how 
experimental amblyopia affects perceptually 
defined mechanisms that support visual sensi- 
tivity to form, contrast, and position. Neuro- 
physiological studies in the same animals then 
reveal alterations in cortical neuron properties 
that seem to be related to the psychophysically 
measured visual defects. 
Using this strategy, we seek to uncover the rela- 
tionship between the neural changes that under- 
lie amblyopia and the perceptual consequences 
of the disorder. We are currently pursuing the 
idea that the relatively mild type of amblyopia 
typically produced by anisometropia (having un- 
symmetric parts) involves a deficit in the P sys- 
tem, while the more complex syndrome that of- 
ten follows strabismus also involves important 
deficits in the M system. 
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