An analysis of asymmetries in cat vertical eye movements generated by sinusoidal pitch.

Asymmetries in the fast and slow components of nystagmus in the cat vertical vestibulo-ocular reflex (VVOR) were analyzed. Sinusoidal pitch stimuli were used in two experimental conditions, one with the animals on their sides and the other with the animals upright. The half-periods of upward and downward slow component position were generally not of equal duration in the on-side condition. Such was not the case for upright pitch where the slow component was symmetric. In addition, the number of fast components in the two directions was not equal with downward-directed predominating regardless of pitch condition. These two results led to the conclusions that gravity plays an essential role in the normal VVOR and fast component asymmetries may be inherent in the reflex.