The acceleration method is used for OKN stimulation. OKN stimulus is gradually increased at an acceleration velocity of 1°/sec². When the appearance of OKN is optimal for the test subject, the light is suddenly turned off. Usually the best range to elicit OKN in humans is 70-80°/sec.
The subsequent OKAN is then recorded by electronystagmography in a completely dark room. Recordings are made for approximately 2 minutes after the light is turned off. The present study evaluated the significance of clinically diagnosing the inversive phenomenon of human OKAN. In normal OKAN, OKAN-I (OKAN in the Ipsilateral Direction) appears in the same direction as the OKN stimulation. In a few cases, OKAN-C (OKAN in the Contralateral Direction)appears in the opposite direction of the initial OKN stimulus. When such reaction is seen bilaterally, this is the inversive phenomenon of OKAN. This phenomenon is never seen in normal subjects. The inversive phenomenon in OKAN is thought to be due to bilateral suppression of OKAN-I and the appearance of OKAN-C immediately after OKN stimulation.
Among 5542 cases in which the OKAN test was performed over a 7 year period, the inversive phenomenon was seen in 258 cases (4.7%). These inversive cases may be classified into 4 major groups. The first group includes cases of unilateral peripheral vestibular disturbance (49 cases), the second, those of bilateral peripheral vestibular disturbance (51 cases), the third, those of cerebrovascular disturbance in the vertebro-basilar artery distribution (103 cases), and the fourth group, others (55 cases).
In clinical experiments, bilateral OKAN-I was suppressed after unilateral anesthesia of the inner ear, followed by the early appearance of bilateral OKAN-C. So in unilateral peripheral vestibular disturbance, vestibular compensation by the vestibulo-cerebellum acts intensively to augment OKAN-C. The intensive expression of such vestibular compensation is thought to represent the inversive phenomenon of the OKAN. According to these results, vestibular compensation from the vestibulo-cerebellum appears to act symmetrically on the right and left velocity storage integrators.

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