Quantitative analysis of salamander horizontal head nystagmus.

The horizontal optokinetic head nystagmus of salamanders (Salamandra salamandra) was investigated at various constant and sinusoidally modulated velocities. With constant velocities the best compensation (head velocity/stimulus velocity) measured was 0.6 at a stimulus velocity of 3 deg/s. With slow stimuli up to 5 deg/s, small oscillations in the slow phase of the nystagmus occurred. The nystagmus started with a delay of 1.1 s after onset of stimulus with an acceleration period of up to 6 s. After the stimulus terminated, the head was decelerated within (on average) 5 s, indicating a weak velocity storage element. The nystagmus frequency, the acceleration time, and the deceleration time were in correlation with the head velocity during the slow phase. With sinusoidal stimuli, nonlinearities were displayed: the gain was amplitude-dependent, and distortions of the sinusoidal head movements occurred with higher frequencies.