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T.L. Alvarez, J.L. Semmlow, A. Daftari, C. Pedrono; Divergence Eye Movements Are Dependent on Initial Stimulus Conditions . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2925.
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Controversy exists among investigations reporting differences between convergence and divergence in terms of each system’s dynamic and temporal characteristics. Here we report that the dynamics of divergence movements not only differ from convergence movement, but depend on the initial vergence position. The Dual Mode Theory states that vergence movements are composed of an transient feedforward component and a sustaining feedback component. This study investigates which component is responsible for the difference in dynamics obversed in the divergence responses. Four subjects were given four degree disparity step changes for convergence and divergence at different initial stimulus positions. Convergence eye movements did not exhibit strong differences in movement dynamics. Conversely, the velocity of divergence eye movements beginning close to the subject was approximately twice that of responses beginning at far. The responses to near stimuli also exhibited shorter temporal properties compared to responses further from the subject. An independent component analysis revealed that the tranient component varies as a function of stimulus position for divergence movements, Figure 1. Hence, while convergence responses are fairly similar irrespective of the initial position, divergence dynamic and temporal properties are dependent on the initial stimulus position. Furthermore, it appears that the transient component of the divergence movement is responsible for this change in neural control.
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