Asymmetries between convergence and divergence reveal tonic vergence is dependent upon phasic vergence function

Journal of Vision
Ian M Erkelens, William R Bobier

Abstract

Horizontal vergence eye movements are controlled by two processes, phasic and slow-tonic. Slow-tonic responses are hypothesized to be stimulated by the faster, pulse-step neural output of the phasic system. This suggests that the general behavior of each system should be similar; however, this relationship has yet to be investigated directly. We characterize the relationship between phasic and tonic vergence by quantifying directional asymmetries in the response properties of each mechanism to the same disparity amplitudes. Four subjects viewed symmetric steps in disparity dichoptically at 40 cm while eye movements were recorded with infrared oculography. First- and second-order phasic and slow-tonic convergence response properties increased linearly with disparity demand (p < 0.01), whereas divergence responses did not (p > 0.05). Phasic divergence responses were slower than convergence (p = 0.012) and were associated with a higher frequency of saccades (p < 0.001). The average rate of slow-tonic change was correlated to the average peak velocity of phasic vergence at the same vergence demand in both directions, r = 0.78, p < 0.0001. Clear directional asymmetries were observed in phasic and tonic vergence responses. The respon...Continue Reading

Citations

Sep 20, 2018·Journal of Neurophysiology·Joseph L Demer, Robert A Clark
Aug 12, 2020·Investigative Ophthalmology & Visual Science·Ian M Erkelens, William R Bobier
Dec 19, 2020·Scientific Reports·Lindsey M Ward, Zoï Kapoula

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