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.
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.
We do this with dreams. Lucid dreaming allows us to modify what we experience.
This is the stock in trade of stage hypnotists. They induce a false or partially false reality in which the subject experiences non-real people, objects and sensations. Self-hypnosis is possible.
This happens with hallucinogens, e.g. peyote.