Simply described, the brain contains several mechanisms
involved in vision. Consider two systems in the brain which evolved at
different times. The first that evolved is more primitive and resembles the
visual system of animals such as fish and frogs. The second to evolve is more
complex and is possessed by mammals.
The second system seems to be the one that
is responsible for our ability to perceive the world around us and the first
system is devoted mainly to controlling eye movements and orienting our attention
to sudden movements in our periphery. Patients with blind sight have damage to
the second, “mammalian” visual system (the visual cortex of the brain and some
of the nerve fibers that bring information to it from the eyes). (Carlson,
2010)
This phenomenon shows that how, after the more complex visual system is
damaged, people can use the primitive visual system of their brains to guide
hand movements towards an object even though they can’t see what they are
reaching for. Hence, visual information can control behavior without producing
a conscious sensation.
