Dynamics of the Disparity Vergence Fusion Sustain Component

Document Type

Article

Publication Date

1-1-2019

Abstract

The stereotypical vergence response to a step stimulus consists of two dynamic components: a high velocity fusion initiating component followed by a slower component that may mediate sustained fusion. The initial component has been well-studied and is thought to be controlled by an open-loop mechanism. Less is known about the slow, or fusion sustaining component except that it must be feedback controlled to achieve the positional precision of sustained fusion. Given the delays in disparity vergence control, a feedback control system is likely to exhibit oscillatory behavior. Vergence responses to 4 deg step changes in target position were recorded in eight subjects. The slow component of each response was isolated manually usinginteractive graphics and the frequency spectrum determined. The frequency spectra of all isolated slow vergence movements showed a large low frequency peak between 1.0 and 2.0 Hz and one or more higher frequency components. The higher frequency components were found to be harmonics of the low frequency oscillation. A feedback model of the slow component was developed consisting of a time delay, an integral/derivative controller and an oculomotor plant based on Robinson’s model. Model simulations showed that a direction dependent asymmetry in the derivative element was primarily responsible for the higher frequency harmonic components. Simulations also showed that the base frequencies are primarily dependent on the time delay in the feedback control system. The fact that oscillatory behavior was found in all subjects provides strong support that the slow, fusion sustaining component is mediated by a feedback system.

Identifier

85102803353 (Scopus)

Publication Title

Journal of Eye Movement Research

External Full Text Location

https://doi.org/10.16910/jemr.12.4.11

e-ISSN

19958692

First Page

1

Last Page

12

Issue

4

Volume

12

Grant

MRI CBET 1428425

Fund Ref

U.S. Department of Health and Human Services

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