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In this fascinating TED-Talk, neurologist and author Oliver Sacks discusses Charles Bonnett syndrome, a strange condition where visually impaired people experience lucid hallucinations.

Our good friend Paul Devereux has written on this topic previously, in Darklore Volume 1 and Fortean Times, and you can find a version of his article at Brainwaving.com. It’s a personal story involving a friend of Paul’s that suffered from Charles Bonnet syndrome, which got him thinking about the ‘reality’ of our perceptions:

The Charles Bonnet Syndrome is merely an observation, not an explanation, so what exactly causes these hallucinations? On that subject the medical literature becomes less helpful, and it is clear, even admitted, that no one really knows. I could buy the idea that patches of light in the central visual region could be related to pathological conditions in the macula, and could cause people and writing to apparently disappear intermittently, but faces at the window, and people dressed in various costumes walking toward churches or driving vehicles or holding street parties seem more of a push. This was especially the case for me in that I was also aware that people claiming to encounter spirits, whether psychic mediums or ordinary individuals in spontaneous cases, tend to report seeing them in their peripheral vision rather than directly, “head on”. I could not help but wonder with these macular degeneration visions whether we were dealing with hallucinations or spirits or some subtle level of perception between them both.

Although the actual mechanics are currently unknown, the basic official theory explaining the visions associated with visual impairment like macular degeneration is that the brain, on receiving incomplete visual data through the eyes, “fills in” the missing elements as best it can – a kind of “best fit” process. In fact, there is evidence that it is only the input of a constant visual stream through our eyes that prevents the brain making up its own imagery in any case. This has been demonstrated in sensory deprivation experiments in which subjects who are placed in total blackout conditions for long periods experience hallucinatory imagery to lighten their darkness. All of us experience this in another form and to a lesser degree when we dream.

If this explanation is true, then a whole host of other implications are raised. If animated figures in costumes, shades of the dead, processions leading to physically real churches, whole landscapes and entire, complex scenes can be rendered in intricate detail by the brain struggling to “fill in” gaps in sensory data, what then is “reality”? Could what we take to be concrete materiality be a kind of hallucination sustained by cultural conditioning, and are paranormal phenomena simply glitches in that illusion? Are the different, spirit-based worldviews held by tribal societies simply other forms of hallucination no less “real” than our own? Is the Hindu doctrine of apparent reality being but the “Veil of Maya”, of illusion, correct?

Whatever the answers are to such questions, one thing is certain – we do not see with our eyes alone.

An interesting point made by Oliver Sacks is that around 10% of visually impaired people have these hallucinations, but only about 1% report it to their doctor, as they fear being labeled “crazy”. It’s a similar predicament to people who have near-death experiences and other seemingly paranormal interactions, and suggests that there is somewhat of a deleterious effect to the growing rationalism of the modern world. In fact, we are strange creatures who regularly see and experience strange things – we shouldn’t “believe” them as a matter of fact, but we should at least acknowledge more often that they are a built-in part of our perceptual range.

Dr. Sacks’ latest book, Hallucinations, which obviously touches on this topic, will be released later this year and can be pre-ordered via the given link.

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