The cerebellum is the part of the brain which coordinates movement and balance (i.e. fine motor skills and coordination). There are 3 areas of the cerebellum that can be underdeveloped in CH cats and the amount of underdevelopment relates to their severity level.
The cerebellum “coordinates movement and balance. The cerebellum received sensory information about the position of the joints and the length of the muscles, as well as input from the auditory (hearing) and visual systems. It also monitors motor commands issued by the cerebrum. Information from the cerebrum passes first to the pons and from there to the cerebellum. The cerebellum integrates this information as it carries out coordination and error checking during motor and perceptual functions. Hand-eye coordination is an example of cerebellar control; if the cerebellum is damaged, the eyes can follow a moving object, but they will not stop at the same place as the object.” – “Biology” 8th Edition by Campbell & Reece