Divergence dynamic modification as a function of initial position.

The ability to change or adapt is critical in the survival of a species. Research has shown that the dynamics of disparity vergence eye movements, the inward (convergence) or outward (divergence) turning of the eyes, are malleable and depend to some extent on the amplitude of preceding stimuli. Divergence eye movements are dependent on initial stimulus position where responses that occur closer to the subject are faster compared to responses that occur farther from the subject. The purpose of this study was to investigate if the modification of divergence eye movements was also a function of initial stimulus position. An experimental trial consisted of three phases: baseline, modification, and recovery. The baseline and recovery phases used only 4 degrees test stimuli. The modification phase consisted of a 4 degrees test randomly intermixed with an 8 degrees step presented in a 1:5 ratio. Two experiments were conducted, one with an initial vergence angle of 8 degrees (far) and the other with an initial position of 20 degrees or 18 degrees (near). Two subjects participated. The dynamic characteristics of the responses to test stimuli were quantified by measuring the magnitude of the peak velocity. Preliminary results suggest the amount of change in peak velocity was greater when the stimuli were closer to the subject. Data suggest that the peak velocity of divergence observed during baseline conditions maybe correlated to the ability to change the dynamics of the disparity vergence system.