Vestibulo‐ocular and optokinetic reactions to rotation and their interaction in the rabbit

1. Compensatory eye movements due to sinusoidal yaw movements on a torsion swing were measured in alert rabbits. A range of combinations of frequencies (0·048–1·8 Hz) and amplitudes (1–25°) were used. Gain (cumulative slow phase eye movement amplitude/swing amplitude) and phase (eye position vs. swing position — 180°) were calculated from averaged records. 2. Eyes were either closed (canal-ocular reactions only), open in earth-fixed visual surroundings (natural interaction of vestibular and optokinetic reactions), or looking at platform-fixed surroundings, which rotated with the animal (conflict situation). In some rabbits, the same stimulus programme was applied a month after bilateral destruction of the labyrinths (optokinetic reactions only). 3. For canal-ocular reactions, no true threshold was found. Yet the system showed a small but systematic non-linearity which is tentatively explained by an acceleration-dependence of gain. For the higher frequencies (0·40–1·8 Hz) used, gain was 0·55–0·75, with a decrease at the lower frequencies, down to 0·16–0·33 at 0·048 Hz. The response showed a phase-lead of about 45° at 0·048 Hz and was nearly in phase at 1–1·8 Hz. The long time constant of the cupula-endolymph system was estimated at about 3·3 sec. 4. With earth-fixed visual surroundings a temperature-independent gain (range 0·55–0·82) with negligible phase error was found for the entire stimulus range tested. This natural combination of canal-ocular and optokinetic systems appears to function very efficiently, with mutual correction of the defects of the systems apart. 5. With platform-fixed visual surroundings the canal-ocular system was severely inhibited and its non-linearities were markedly enhanced by the optokinetic system, especially when the torsion swing moved slowly. 6. The general shape of input—output relations of optokinetic reactions after labyrinthectomy were similar to those found earlier in normal animals, but gain was subnormal for the entire stimulus range tested.