INITIAL COMPONENT CONTROL IN DISPARITY VERGENCE - A MODEL-BASED STUDY

The dual-mode theory for the control of disparity-vergence eye movemen ts states that two components control the response to a step change in disparity, The initial component uses a motor preprogram to drive the eyes to an approximate final position, This initial component is foll owed by activation of a late component operating under visual feedback control that reduces residual disparity to within fusional limits, A quantitative model based on a pulse-step controller, similar to that p ostulated for saccadic eye movements, has been developed to represent the initial component, This model, an adaptation of one developed by Z ee et al, [1], provides accurate simulations of isolated initial compo nent movements and Is compatible with the known underlying neurophysio logy and existing neurophysiological data, The model has been employed to investigate the difference in dynamics between convergent and dive rgent movements, Results indicate that the pulse-control component act ive in convergence is reduced or absent from the control signals of di vergence movements, This suggests somewhat different control structure s of convergence versus divergence, and is consistent with other direc tional asymmetries seen in horizontal vergence.