Increasing evidence indicates that the oculomotor response to a near stimulus (which includes lens, pupil,, and vergence eye movements) is guided largely by neural processes driven by disparity stimulation. The traditional notion that disparity vergence is controlled by continuous feedback has been rejected by recent findings. These experiments show that disparity vergence and its associated near triad responses are controlled by at least two subcomponents which have different response behaviors and are driven by different features of the disparity stimulus. One of these components, the one responsible for controlling the fast portion of disparity vergence, shows indications of sampling and preprogramming reminiscent of saccadic behavior. Experiments proposed would isolate the two components by identifying stimulus features which selectively drive each of them. Subsequent experiments will define the basic operating mode of each component (feedback controlled or preprogrammed), and determine the critical timing parameters associated with the fast component. Even if the fast component is not preprogrammed, its behavior cannot be explained as a simple error- driven control process. Hence a final set of experiments will define the relationship between specific stimulus features and the fast component response. A primary objective of this proposal is the development of a theory of disparity vergence control. This theory will be implemented as a quantitative, computer-simulated model and evaluated in terms of the experimental findings. The research proposed is part of a long-term objective to develop a comprehensive theory of near triad control to provide a deeper and more consistent explanation of clinical and experimental behaviors.
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