By a combination of “separation of the visual field” and “ the overlapping method”, the author has studied the optokinetic nystagmus induced by foveal vision and peripheral vision as well as the optokinetic nystagmus in artificial hemianopsy. Optokinetic response was recorded by DC-ENG in five healthy adults, to whom constant speed stimulation (10-120°/sec.) was administered using a projection-type optokinetic stimulator. Results obtained are as follows.
(1) The nystagmus induced by foveal stimulation begins with a slow phase, whereas that induced by peripheral field stimulation begins with a quick phase.
(2) With foveal vision the slow phase velocity of nystagmus, at low stimulus speeds, is equal to the speed of the target. At higher speeds the slow phase velocity falls below that of the target speed. With peripheral vision, the slow phase velocity is often slower than the speed of the target even in the slow speed range.
(3) Peripheral vision supports foveal vision subsidiarily, and this supporting effect is more evident in the high speed range of optokinetic nystagmus.
(4) Temporal and nasal hemianopsies have the same properties against optokinetic stimulation.
(5) There is no essential difference between the optokinetic nystagmus induced by nasotemporal and temporonasal stimulations.
(6) When foveal vision is reserved, there is no remarkable difference between the optokinetic nystagmus in hemianopsy induced by foveopetal and foveofugal stimulations.
(7) In the case of hemianopsy whose foveal vision is involved, the nystagmus during foveofugal stimulation is very fine and irregular, in contrast to the nystagmus during foveopetal stimulation which is well induced almost comparable to the normal eye.
(8) Foveal vision is very important for formation of the slow phase of optokinetic nystagmus.
(9) Foveopetal movement of an image in the peripheral retina is very important for formation of the quick phase, and is stronger than foveofugal movement in the peripheral retina as a stimulus to attract the eye.
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