Is it possible to block out reality completely? Is it possible for an individual to block out all reality and see objects, colors and hear voices and sounds that are non-existent non-stop?
Yes, it is. Seeing objects, colors, hearing voices and sounds are electrical impulses translated by our sensorial organs and sent to the brain. There are cases of blind people which can "see" (feel?) a whole load of abstract images, and are actually bothered by it.

A person could have no sensing organs and still have electrical impulses by means of artificial brain stimulus, or due to a neurological damage; tinnitus comes to mind (no pun intended).


  When TMS [transcranial magnetic stimulation] is applied with a single pulse to motor or sensory cortex, it is possible to evoke a motor or sensory response. When the sensory cortex is visual cortex, the response is a phosphene.4 Phosphenes are the sensation of light in the absence of visual stimulation.