Laboratory of Sensorimotor Research, National Eye Institute, National Institutes of Health, DHHS, Bethesda, Maryland 20892-4435, USA
Address for correspondence: Dr. Lance M. Optican, Bldg. 49, Room 2A50, Laboratory of Sensorimotor Research, National Eye Institute, NIH, Bethesda, MD 20892-4435. Voice: 301-496-9375; fax: 301-402-0511. LanceOptican{at}nih.gov
Visually guided movements require the brain to perform a sensorimotor
transformation. The key to understanding this transformation
is to understand the different roles of the superior colliculus
(SC) and cerebellum (CB). The SC has a three-layered structure.
Cells in the top layer have visual, but not motor, responses.
However, cells in the deeper layers have both visual and motor
responses. Thus, for a long time it was thought that the SC
encoded both the retinal location of a sensory stimulus and
the desired change in eye movement needed to acquire it. However,
copious evidence has accumulated that shows that the SC encodes
only the retinal location of a visual target, and not the movement
needed to foveate it. Thus, the information needed to make accurate
movements must come from another part of the brain, which is
proposed to be the cerebellum. Here it is shown how the cerebellum
could perform the sensorimotor transformation.
