In order to study the influence of caloric stimuli on optokinetic nystagmus, 10 normal subjects were tested by applying to them horizontal optokinetic stimulation together with the caloric stimulation. The optokinetic stimuli were given by a slit projection type stimulator. Twelve white stripes (3cm wide) were projected on the screen at equal distance, rotated with an angular acceleration of 4°/sec
2 until stimulus speed attained to 180°/sec and uniform velocity (30°/sec, 60°/sec and 120°/sec). The caloric stimuli were the same as those applied by Hallpike, i. e. each ear was irrigated with water of 30° for 40 seconds. The optokinetic nystagmus was recorded by ENG (time constant 3.0 and 0.03).
The results obtained as follows:
1) The optokinetic nystagmus was increased in total frequency, maximum eye speed of retinal nystagmus and optokinetic adaptation limit when the simultaneously applied caloric stimulation created identically directed eye motions. On the other hand, the optokinetic nystagmus was decreased when the caloric stimulation was reversed.
2) The foveal nystagmus was not increased, but decreased in eye speed of the slow phase by the caloric stimulation.
3) The retinal nystagmus was increased and decreased in frequency and eye speed of the slow phase by the caloric stimulation.
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