The Frontal Cortex

The Hallucinations of Consciousness

Posted by Jonah Lehrer on February 6, 2008
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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.

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  1. #1 Oran Kelley
    February 6, 2008

    consciousness is like a salesman for sensation

    What do you figure this means? I can’t make the image work.

    For one thing, who would consciousness be selling perception to? And a salesman essentially tries to get you to do one thing with your money rather than another. What is the currency in your imagined consciousness transaction, and what are the spending/inverstment alternatives?

    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.

    I’d point out here that there is another alternative: consciousness could pay attention to abstractions, ideals, and non-hallucinatory memories, but interestingly enough it goes beyond this in cases like you outline above.

  2. #2 Jonah
    February 6, 2008

    Good questions, all of them. I should have been more clear. I assume that consciousness is selling sensations to the self. (Don’t ask me where the self comes from. i discuss that scientific problem at length in the Virginia Woolf chapter in my book. The short answer is that the self remains an utter mystery.) I also don’t mean to suggest that the self somehow precedes consciousness. Rather, i imagine the two are completely knotted together. You can’t have one without the other. The self is the perceiver of our perceptions, but our consciousness might be what makes those perceptions worth perceiving in the first place.

    Obviously, calling these half-assed thoughts “speculations” is an understatement. But I do think Humphrey has an interestng take on what sort of questions we should be asking about the purpose of consciousness.

  3. #3 jb
    February 6, 2008

    Jonah’s entry brings to mind a meditation practice called “dark retreat” in which one stays alone in a completely dark place 24/7 for a length of time. One does have food on hand or one is brought food so it is not without smell and taste; it is also very quiet. When one is formally meditating in dark retreat one would not be moving so feeling in the body would be minimized. Wikipedia’s definition seems accurate. People only do these retreats after they have had experience in investigating the nature of mind under less extreme conditions, and with the supervision of an experienced teacher.

  4. #4 Mark P
    February 6, 2008

    This is really no surprise, since we do not see with the eye but rather with the brain. It is similar if not identical to the phantom limb sensations reported by amputees. I think there is not much mysterious about it.

  5. #5 Rachael
    February 6, 2008

    >”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”

    Reference the recent Friday discussion about the mind altering effects of marijuana!

    Does anyone know if people blind from birth have any activity in visual areas? It seems like they shouldn’t. I thought I remembered reading something about how other sensory modes take over that physical space in the brain….

  6. #6 Andrea Grant
    February 7, 2008

    But is this true only for those who were previously sighted? Do people who are born blind have visual hallucinations or does the brain just turn off that channel? I remember reading one of Oliver Sacks’ case histories about a man who was able to become sighted in his 50s after a lifetime of blindness, but no had realized his brain would have to learn how to see–to decode the information coming from the eyes.

    Does this also happen with hearing loss? I know tinnitus can be “induced” in almost anyone by putting them in a absolutely silent environment for long enough, but I’d hardly compare my tinnitus with a winking soldier!

  7. #7 Mark P
    February 7, 2008

    Andrea, there was a story on NPR this week, I think, about a man who had suffered severe hearing loss over a long period. He started “hearing” music. After surgery to improve his hearing, he could hear real music, but not with the same frequency response. As a result, music sounded tinny. However, he said that he still hears phantom music with the same fidelity he had when he was able to hear normally.

  8. #8 alternative medicine hiv
    August 17, 2011

    I really dont understand why some people feel the need to be so argumentative.