Mechanism for Voluntary Cancellation of the Vestibulo-ocular Reflex in Squirrel Monkeys That Is Not Related to Smooth Pursuit

The vestibulo-ocular reflex (VOR) is reduced or cancelled by a smooth pursuit eye movement programmed to match the velocity of the moving target whenever there is an attempt made to follow a moving visual target by combining a smooth pursuit eye movement with a head movement generated in the direction of target movement. The objective of this study is to determine if there is a second mechanism that can cancel the VOR. The experiments in this study involved four squirrel monkeys that were prepared for chronic recording of eye movements. The monkeys were seated on a vestibular turntable with restrained heads. Their eye movements were recorded using magnetic search coil technique. Results showed that there is a cancellation of the vestibulo-ocular reflex generated by the sudden turntable jerks. There is also a cancellation of the vestibulo-ocular reflex produced by the unpredictable head movements.