Coding of visual information by units in the cat cerebellar vermis

Extracellular records were made of the responses to precisely controlled stationary or moving visual stimuli of 174 units in the cerebellar vermis of cats anaesthetised with chloralose. Identified Purkinje cells and unidentified units responsed similarly. Responses to ON and to OFF steps of a stationary light bar had different characteristics. Some units showed changes in the form of their ON responses related to different positions of the stimulus in their large receptive fields. In some cases changes in response latency from different field positions were also noted. Some units responded only to binocular stimulation and others gave much larger responses to binocular than to monocular stimulation. In addition, some were sensitive to the relative retinal disparity of images and, of these, several were sensitive to vertical as well as to horizontal retinal disparity. Sinusoidally-moving light bars gave responses consisting of one or two bursts of impulses per cycle; the most effective frequency was about 3 Hz. These responses may represent detection of the instant of maximum velocity. The relatively precise coding of retinal disparity in spite of the large size of receptive fields and the coding of position within these large fields is discussed. A possible function for the disparity-sensitive units in the control of vergence is suggested and the relation of this control to visual depth detection and to the estimation of the absolute distance of objects from the animal is discussed.