Intrabeat relationship of postrotatory nystagmus in normal subjects.

Intrabeat relationships between duration, amplitude and velocity of the slow phase of nystagmus and between amplitudes of the fast and slow phase of nystagmus were analysed from postrotatory responses in 10 normal subjects, using linear regression analysis. For 5 subjects, the tests were repeated five times. Highly significant correlation was found between velocity and amplitude of the slow phase in 9 of 10 subjects, whereas in one subject it was less significant. All subjects exhibited a significant correlation between velocity and duration of the slow phases. These intrabeat relationships were repeatable and representative for each individual. Highly significant correlation was found between amplitudes of the slow and fast phases of nystagmus in all subjects. No interindividual differences in these variables could be observed. The results indicate that the end-point of the slow phase of vestibular nystagmus in darkness is controlled by positional and durational corollary circuitries. The positional signal in displacement circuitry is probably derived by integration of the velocity signals from the labyrinths. The durational circuitry is presumably more dominant at high nystagmus velocities in order to permit sufficient time for fixation.