The Visual System:
   exemplifies the brain's array of subsystems.   There is a pathway to the superoptic nucleus of the Hypothalamus that controls daily rhythms of such behaviors as sleeping and feeding (A).   There is a pathway to the pretectum in the midbrain which controls pupillary responses to light (B).   A pathway travels to the superior colliculus in the midbrain which controls head orienting to objects (C).   Another pathway leads to the Pineal Gland (D), controlling the long-term cicadian rhythms of the body.  

   Additionally, a pathway to the accessory optic nucleus (E) is present, which moves the eyes in compensation for head movements.   There is, of course, a pathway to the Visual cortex (F) that controls pattern perception, depth perception, color vision, and the tracking of moving objects.   And finally a pathway leads to the Frontal cortex (G) which controls voluntary eye movements.

      A great deal of human memory is devoted to vision. 

The  Visual  Subsystems

Visual System	Function
(A) Superoptic Nucleus (of the Hypothalamus)	Controls daily rhythms (sleep, eating, etc.) in response to day-night cycles.
(B) Pretectum	Produces changes in pupil size in response to light intensity changes.
(C) Superior  Colliculus	Head orienting, particularly to objects in the peripheral visual fields.
(D) Pineal  Body	Long-term Cicadian Rhythms.
(E) Accessory  Optic  Nucleus	Moves eyes to compensate for head movements.
(F) Occipital  Lobe	Color Vision.
(G) Frontal  Lobe Eye Fields	Voluntary Eye Movements.