Independent component analysis of divergence eye movements

Vergence eye movements are the inward (convergence) or outward (divergence) turning of the eyes which allows humans to view objects in depth. Previous studies on the dynamics of convergence and divergence eye movements have produced varied, sometimes contradictory, results. Four subjects were studied and tracked four degree disparity step changes for convergence and divergence at different initial target positions. Here we report that the dynamics of divergence movements not only differ from convergence movement, but depend on the initial vergence position. Velocities of divergence eye movements in response to targets that were initially near to the subject were approximately twice that of responses to initially distant targets. Hence, while convergence responses are fairly similar irrespective of the initial position, divergence dynamic properties are dependent on the initial stimulus position. It is speculated that the differences observed in divergence may be the result of a difference in the underlying neural controller potentially a difference in the magnitude of the fusion initiating component. Preliminary data using independent component analysis (ICA) shows the divergence system contains a step and pulse where the amplitude of the pulse is dependent on the initial stimulus position.