Now this, for me, is a common situation. I work in old-age homes, largely.
I see a lot of elderly people who are hearing impaired or visually impaired.
About 10 percent of the hearing impaired people get musical hallucinations.
And about 10 percent of the visually impaired people get visual hallucinations.
You don't have to be completely blind, only sufficiently impaired.
Now with the original description in the 18th century, Charles Bonnet did not have them.
His grandfather had these hallucinations. His grandfather was a magistrate, an elderly man.
He'd had cataract surgery. His vision was pretty poor. And in 1759, he described to his grandson various things he was seeing.
The first thing he said was he saw a handkerchief in midair. It was a large blue handkerchief with four orange circles.
And he knew it was a hallucination. You don't have handkerchiefs in midair. And then he saw a big wheel in midair.
But sometimes he wasn't sure whether he was hallucinating or not, because the hallucinations would fit in the context of the visions.
So on one occasion, when his granddaughters were visiting them, he said, "And who are these handsome young men with you?"
And they said, "Alas, Grandpapa, there are no handsome young men." And then the handsome young men disappeared.
It's typical of these hallucinations that they may come in a flash and disappear in a flash.
They don't usually fade in and out. They are rather sudden, and they change suddenly.
Charles Lullin, the grandfather, saw hundreds of different figures, different landscapes of all sorts.
On one occasion, he saw a man in a bathrobe smoking a pipe, and realized it was himself.
That was the only figure he recognized. On one occasion when he was walking in the streets of Paris, he saw -- this was real -- a scaffolding.
But when he got back home, he saw a miniature of the scaffolding six inches high, on his study table.
This repetition of perception is sometimes called palinopsia.