"I had been reading about the color indigo, how it had been introduced into the spectrum by [Isaac] Newton rather late, and it seemed no two people quite agreed as to what indigo was, and I thought I would like to have an experience of indigo. And I built up a sort of pharmacological launchpad with amphetamines and LSD, and a little cannabis on top of that, and when I was really stoned I said, 'I want to see indigo now.' And as if thrown by a paintbrush, a huge pear-shaped blob of the purest indigo appeared on the wall.

"Again it had this luminous, numinous quality; I leaped toward it in a sort of ecstasy. I thought, 'This is the color of heaven.' ... I thought maybe this is not a color which actually exists on the Earth, or maybe it used to exist or no longer exists. All this went through my mind in 4 or 5 seconds, and then the blob disappeared, giving me a strong sense of loss and heartbrokenness, and I was haunted a little bit when I came down, wondering whether indigo did exist in the real world.

"I would turn over little stones. I once went to a museum to look at azurite, a copper mineral which is maybe the nearest [to] indigo, but that was disappointing. I did in fact have that experience again, but when I had it the second time, it was not with a drug, it was with music — and I think music can take one to the heights in a way comparable with drugs."

Oliver Sacks à propos de son livre Hallucinations, Knopf, 2012 dans l'émission Fresh Air de Terry Gross du 6 novembre 2012, sur NPR