The Effect of Blockage of All Six Semicircular Canal Ducts on Nystagmus Produced by Dynamic Linear Acceleration in the Cat

Abstract

Seven cats were given rotary tests about an earth-vertical axis and also about an earth-horizontal axis. They were tested with the sagittal head plane in the plane of rotation as well as with the horizontal head plane in the plane of rotation. Recordings of eye movements were made during the tests. Following surgical transection and blocking of all six semicircular ts canal ducthe cats were tested again. It was found postoperatively that horizontal and vertical nystagmus in response to angular acceleration about an earth-vertical axis were abolished. Nystagmus during constant velocity rotation about an earth-horizontal axis remained, however, although the slow phase eye velocity and frequency of the nystagmus were reduced. From these and other data it is suggested that although continuity of the semicircular canal ducts is necessary for the nystagmus in response to angular accelerations about a vertical axis, it is only contributory (and not necessary) for the nystagmus during constant velocity rotation about an earth-horizontal axis. These findings and conclusions are discussed in the context of existing data and theory.