Deprive the mind of sensory stimuli, and what does the mind do? It starts to hallucinate. It invents perceptions amid the emptiness, filling in the void with make-believe. This is known as Charles Bonnet syndrome, and it affects approximately 10 percent of who go blind:
It took almost 50 years, but slowly, slowly David Stewart went blind.
A former long-time executive at the Corporation for Public Broadcasting in Washington, D.C., Stewart has a hereditary disease, retinitis pigmentosa, which affects the rods and cones in his eyes. In his 20s, his vision narrowed. By the time he hit 80, he was almost totally blind.
But then he discovered that sometimes blindness comes with a bonus.
One day while listening to a book on tape — 1776 by David McCullough — he heard how American sailors helped George Washington sneak cannons and horses across the Hudson River to escape the British.
As Stewart mused about those sailors, very strangely, one of them appeared in his head — not a dreamy fantasy, but a vivid, highly detailed, very real-like hallucination.
“He had on a cap, a blue cap with a polished black beak and he had a pipe in his mouth.” The sailor gazed right at Stewart. Then he winked. Stewart was amazed.
Stewart was, at this point, very blind. He had lost his memory for color — for blues, yellows and reds — and he lived in a black and white world. But when his sailor arrived, “There it was!” he exclaimed. “The first color I had seen for a considerable amount of time!”
Fascinating stuff. But I think psychological phenomena like Charles Bonnet syndrome shed light on the larger purpose of consciousness. Nicolas Humphrey said it well in his recent Seed essay:
I want to suggest the role of phenomenal consciousness may not be to enable us to do something we could not do otherwise, but rather to encourage us to do something we would not do otherwise: to make us take an interest in things that otherwise would not interest us, or to mind things we otherwise would not mind, or to set ourselves goals we otherwise would not set.
In other words, consciousness is like a salesman for sensation. As a result, even when there are no visual sensations to sell – the retina no longer captures photons – our conscious mind can’t help but invent its own perceptions. It needs to be interested in things, even if there is nothing out there to be interested in.