That’s how people are training computers to see, too: through visual experience. How the neural network is seeing, then, may be more revealing than what it sees. Which is, of course, what Google engineers set out to explore in the first place.

“We actually ‘see’ things that aren’t there all the time,” said Jeffrey Guss, a psychiatrist at NYU who has studied how treatments involving psilocybin, the psychoactive agent found in some mushrooms, may help cancer patients. “Our visual cortex—not our eyes—are programmed to look for recognizable patterns … to see something in the information that our eyes provide. There are dozens of psychology experiments that show we often see what we expect to see, what we're told we are going to see, rather than what is actually there."

Another way to think about hallucinating is as a kind of connective tissue between what we see and what our brain expects. The fact that hallucinations themselves are, at times, surprising to the person experiencing them, doesn’t change the fact that they can represent the brain’s attempt to grasp for meaning. That doesn’t, however, mean that the images or shapes that appear are meaningful in and of themselves. “While visual hallucinations are sometimes a part of psychedelic experiences, we don’t really consider them terribly important in the big picture of how we use them or think about them,” Guss said. “We’re much more drawn to the ways that they alter meaning and provide a unique experience of the self-than the visuals, which are usually seen as entertaining and interesting, but not with that much intrinsic meaning.”

Although hallucinations are often associated with drug culture, people routinely have bizarre visual experiences even when they aren’t under the influence. In his book, Hallucinations, the late neurologist Oliver Sacks argued they are far more common experience than many people realize. “In other cultures, hallucinations have been regarded as gifts from the gods or the Muses, but in modern times they seem to carry an ominous significance in the public (and also the medical) mind, as portents of severe mental or neurological disorders,” he wrote in The New York Times in 2012. “Having hallucinations is a fearful secret for many people—millions of people—never to be mentioned, hardly to be acknowledged to oneself, and yet far from uncommon.”

In a 2009 TED talk, Sacks recalled his conversation with a 95-year-old woman who was blind but worried she was losing her mind when she began seeing bizarre things.

So I said, "What sort of things?" And she said, "People in Eastern dress, in drapes, walking up and down stairs. A man who turns towards me and smiles. But he has huge teeth on one side of his mouth. Animals too. I see a white building. It's snowing, a soft snow. I see this horse with a harness, dragging the snow away. Then, one night, the scene changes. I see cats and dogs walking towards me. They come to a certain point and then stop. Then it changes again. I see a lot of children. They are walking up and down stairs. They wear bright colors, rose and blue, like Eastern dress.” Sometimes, she said, before the people come on, she may hallucinate pink and blue squares on the floor, which seem to go up to the ceiling. I said, "Is this like a dream?" And she said, "No, it's not like a dream. It's like a movie." She said, "It's got color. It's got motion. But it's completely silent, like a silent movie." And she said that it's a rather boring movie. She said, "All these people with Eastern dress, walking up and down, very repetitive, very limited."

In human brains, bizarre image perception is associated with issues in the eyes, in the brain, and other conditions: migraines, fever, and seizures, for example. In computer brains, such imagery suggests that artificial brains are more human than they may seem. “The fact that humans report that Google’s Inceptionism looks to them like what they see when they hallucinate on LSD or other drugs suggests that the machinery ‘under the hood’ in our brains is similar in some way to deep neural networks,” said Jeff Clune, an assistant professor of computer science at the University of Wyoming.