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Original Article

A Comparison Between two Types of Visually-Evoked Nystagmus in the Monkey

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Pages 30-37 | Published online: 08 Jul 2009
 

Abstract

Similarities between optokinetic nystagmus (O.K.N.) and flicker-induced nystagmus (F.I.N.) include: response buildup and occurrence during the entire period of stimulation; absence of habituation; after-nystagmus in the same direction; occasional after-after-nystagmus to the opposite side; frequency spectrum, peak frequency and existence of lower and upper frequency thresholds. Phenomena are different in that for O.K.N. the stimulus is in motion; binocular and monocular stimulation are effective; direction is determined by direction of motion; unidirectionality is absent; there is minimal influence of background illumination, posture, labyrinthine receptors, and section of crossed optic fibers. For F.I.N. the stimulus is stationary; the response is elicited only by monocular stimulation; the direction is determined by the stimulated eye; there is exclusive unidirectionality; it is abolished by background illumination, optic chiasm section and bilateral labyrinthectomy; it is strongly influenced by posture. This comparison suggests that O.K.N. and F.I.N. are separate responses and that the effective stimulus for F.I.N. may activate selectively the crossed optic fibers.

RÉSUMÉ

Les resemblances entre le nystagmus optocinétique (O.K.N.) et le nystagmus induit par la scintillation (F.I.N.) sont: réponse en accroissement et occurrence pendant la période entière de stimulation; manque d'habituation; aprèsnystagmus dans la měme direction; occasionnelle-ment après-aprèsnystagmus vers le côté opposé; spectre de fréquence, sommet de fréquence et existence de seuils de fréquence inférieur et supérieur. Les épiphénomènes sont differents puis que pour O.K.N. le stimulus est en mouvement; les stimulations monoculaires et binoculaires sont efficaces; la direction est determinée par la direction du mouvement; l'unidirectionalité est absente; Fin-fluence de l'illumination de fond, de la posture, des recepteurs labyrinthiques et de la coupe du chiasma opti-que, sont minimes. Pour F.I.N., le stimulus est station-naire; la réponse est provoquée seulement par la stimulation monoculaire; la direction est determinée par l'œil stimulé; l'unidirectionalite est totale; la réponse dispa-rait si le fond est illuminé, le chiasma est sectionné, ou s'il y a une labyrinthectomie bilatérale. La posture à une forte influence. Cette comparaison suggère que l'O.K.N. et le F.I.N. sont des réponses différentes et que le stimulus effectif pour le F.f.N. peut activer avec predominance les fibres optiques croisées.

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