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A Robust, Normal Ocular Motor System Model with Latent/Manifest Latent Nystagmus and Dual‐Mode Fast Phases
Author(s) -
JACOBS JONATHAN B.,
DELL'OSSO LOUIS F.
Publication year - 2002
Publication title -
annals of the new york academy of sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.712
H-Index - 248
eISSN - 1749-6632
pISSN - 0077-8923
DOI - 10.1111/j.1749-6632.2002.tb02895.x
Subject(s) - clinical neurophysiology , medicine , library science , psychology , neuroscience , computer science , electroencephalography
The fast phases of LMLN may either cause the target image to fall within (foveating) or outside (defoveating) the foveal area. We verified that both types are generated by the same mechanism as voluntary saccades and propose a hypothetical, dual-mode mechanism (computer model) for LMLN that utilizes normal ocular motor control functions. Fixation data were recorded from subjects with LMLN using both infrared and mag netic search coil oculography and used as templates for our simulations. Fast-phase amplitude vs. both peak velocity and duration of simulated saccades were equivalent to those of saccades in normal subjects. Based on our LMLN data, we constructed a hypothetical model in which the slow-phase velocity acted to trigger the change between foveating and defoveating LMLN fast phases. Foveating fast phases were generated during lower slow-phase velocities whereas, defoveating fast phases occurred during higher slow-phase velocities. The bidirectional model simulated Alexander's law behavior under all viewing and fixation conditions. Our ocular-motor model accurately simulates LMLN-patient ocular motility data and provides a hypothetical explanation for the conditions that re sult in both foveating and defoveating fast phases. As is the case for normal physiological saccades, position error determined saccadic am plitudes for foveating fast phases. However, final slow-phase velocity determined amplitudes of defoveating fast phases. In addition, we sug-