I am not a doctor.
That said: shared hallucinations are a rare form of a shared psychiatric disorder or, to use the older, more romantic name, folie a deux. Usually shared disorders take the form of a shared delusion; that is a belief without external justification. An extremely well-known instance was the case of Bo and Peep, the founders of the “Heaven’s Gate” UFO movement which eventually ended in a mass suicide.
Such phenomena most often occur between a dominant personality, often someone who is schizophrenic, and a partner who is a subordinate in the relationship.
Although much rarer, shared hallucinations are well-documented. Sometimes a person may be deluded that they remember having had the same “vision” or other experience as another person, but it is well-established that two people can have the same hallucination at the same time.
Or perhaps we should say “more-or-less the same hallucination”. Mass religious visions make an interesting source for study. People who were at Fatima, Portugal on the day that the sun “danced in the sky” are said to have later given widely divergent descriptions of what St. Mary was supposed to look like, although they were able to take their cue as to where she was by observing the children who were said to be in a religious ecstasy. (People who are disposed to believe in the Fatima visions can, of course, argue that the experience of the children was genuine, but that some of the onlookers were merely victims of the power of suggestion).
Shared hallucinations arise when people are under unusual stresses, such as the influence of certain drugs. The general opinion seems to be that the phenomenon is similar to shared delusions; one person generally takes on a dominant role, and convinces the other person that they are seeing the same thing–although their descriptions of what they saw may differ widely in details later.
When I was about seven–this was in the early 60s–there was a tense drama played out over many days as rescue workers searched for possible survivors of a coal mine disaster in the eastern United States. It was thought that three men might have survived, and that two of them would be together.
It was my family’s habit to listen to the news on the radio at dinner time, and I remember hearing updates on the story night after night. The two men who had been trapped together were eventually rescued. And they told a hair-raising story about something which had happened to them during their confinement which has stayed with me ever since.
One day they saw that there was a door in the wall of the shaft where they were trapped. Somehow they had never noticed that before. It opened, and the other miner–the one who was never rescued, walked past them and went through it. There was a stairway inside, and the two men were agreed that it led to a mine building with which they were familiar. The door shut behind them, and they damaged their hands as they clawed at the wall trying to open it again.
Yes: one miner had noticed the door before the other, and had described what he was seeing.
It seems to me that a great many shared delusions are of a more mundane and benign nature.
After the novelist James T. Farrell died in 1978, a movie critic (it was Siskel or Ebert; I’m sorry, but I don’t remember which) wrote an article in which he told about how he and Studs Terkel had once shown a British writer around Chicago. When Terkel told her that he had gotten his name from Farrell’s character Studs Lonigan, the woman had said that the one thing she wanted to see before leaving Chicago was the park bench where Studs Lonigan and Lucy Scanlan kissed for the first time. Farrell tended to be exact in his description of real places, and after a search, they found it.
I though this was a charming story: here all three of these people knew perfectly well that Lucy and Studs were fictitious characters, but they went on a kind of pilgrimage to find the park bench anyway.
I still found the story charming after I read the Studs Lonigan Trilogy and learned two things. First, Lucy and Studs kissed for the first time at the Lonigan house. Second, nowhere in any of the three novels do the two of them sit together on a park bench. Yet three very people familiar with the novels were apparently able to convince themselves that they remembered reading this after one of them described it.
Similarly, around 1979 a reporter for The St. Louis Post-Dispatch wrote a column in which she said she had met a man who asked pretty much everyone he met if they had read a novel which began “Winter came late that year.” He said that lots of people said it sounded familiar, but nobody could tell him what the book was.
Searching for the book became a kind of protracted treasure hunt in and around St. Louis for a period of months, but no one ever found a book with that opening line. My guess is that there never was one, and the phrase seems so plausible as an opening line that many people convinced themselves that they remembered it when they didn’t. I’ve suspected that it may even be that the columnist made up the story about meeting a young man who wanted to find the book.
And then there was Charles Fort’s story about the couple who complained to the management that the floor of their hotel room was missing…
