The cat's vestibulo-ocular reflex.

1. The conscious cat's vestibulo-ocular reflex (v.o.r.) has been studied using the electro-oculogram to measure eye movements. A servomotor was used to rotate the head horizontally while the body remained stationary. 2. The frequency content of natural head movements in the cat has been determined by Fourier analysis. The fastest and most kinked head movement profiles contain frequency components of significant power extending up to 7-10 Hz. 3. The transfer function of the v.o.r. slow-phase response was measured in the frequency range 0.2-7 Hz. At 1 Hz the average gain is 0.94 with a phase lead of 3 deg. At 7 Hz the gain has only fallen to 0.81 and the phase lag is 10 deg. This indicates that the v.o.r. can compensate to a considerable degree for the high-frequency components of natural head movements. 4. Rotation of the body around a stationary head in the absence of vision does not produce a measurable neck-ocular reflex. 5. The presence or absence of fast phases has no effect on the phase lead of the v.o.r. slow-phase response at 0.2 Hz. 6. V.o.r. fast phases never occur more frequently than 4/sec. 7. Fast phases do not function merely to recentre the eyes once a slow phase has driven them to extreme orbital eccentricities. Instead, fast phases occur early on and serve to offset gaze in the same direction as the head movement.