CONVERGENCE AND DIVERGENCE EXHIBIT DIFFERENT RESPONSE CHARACTERISTICSTO SYMMETRICAL STIMULI

The dynamic characteristics of horizontal convergence and divergence e ye movement responses to symmetric stimuli were examined. Binocular ey e movements were recorded in five, visually normal adult subjects usin g the infrared reflection technique for symmetric convergent and diver gent blur-free, disparity-only, step stimuli of 2, 4, 8, 12, and 16 de g. The main sequence as well as other temporal parameters including la tency, time-to-peak velocity, time constant, and total duration were a nalyzed. A number of fundamental differences in the response character istics were found between convergence and divergence. First, the slope of the peak velocity vs amplitude curve was approximately twice as hi gh for convergence than divergence. The results are consistent with ne urophysiological findings in monkeys and most findings in humans. Seco nd, the initial fast component for convergence exhibited a larger ampl itude than for divergence. This may reflect differences in central neu ral gain far convergence and divergence. And, third, all temporally re lated components were shorter for convergence than divergence. These f indings provide an overall framework for vergence control and suggest fundamental differences in neural processing delays and neural control ler pathways for convergence and divergence. (C) 1997 Elsevier Science Ltd.