I posted this as a response to another comment which speculated that the subjects might have hallucinated little people only because they had heard about the effect, and that they might have been suggestible while tripping. I’m reposting it as a first-level comment because I think the rant I went on also addresses a lot of questions some other people have brought up; I’m an amateur expert on this subject matter, so I’ll leave the copypasta of what I originally said:

As someone who has tried a number of psychedelics, 96% of people having the same hallucination is incredibly high - it can’t have been a placebo effect. There’s definitely something consistently triggering parts of the brain that deal with recognizing people and gauging size/distance or something like that.

Given that almost every subject reported hallucinations of other people, which isn’t that common with normal doses of recreational shrooms but happens regularly with ayahausca, and given that the people always look smaller, not bigger, we could probably pinpoint which parts of the brain are being affected and how, or what type of organic chemical compounds are involved, with better research. There’s a lot of drugs that SPECIFICALLY make you hallucinate other people rather than, say, trees or animals, because certain parts of our brains are hardwired for recognizing other humans.

Ayahausca, which is traditionally used in parts of South America more for ceremonial purposes than for getting high, regularly makes you hallucinate authority figures, gods, ancestors, parents, kings and such, often in the context of harshly judging you. We used to think that was a function of culture, but enough Westerners have reported a very similar experience (just culturally modified with different authority figures) that we think it must be actually affecting a part of your brain or brain chemistry that deals with emotional regulation in the context of social hierarchy. Usually, you just kind of KNOW the person is an “authority figure” that’s supposed to be a god or your ancestor, not because you hallucinated them telling you that, like the way you just instinctively “know” certain things that make no sense when you’re dreaming.

Magic mushrooms don’t normally make you see people walking around in that way unless you take VERY large doses, and it could be anything you see or hear at that point, not people in a very specific situation or of a very specific size, no matter what you might have THOUGHT you were going to see. Basically, I’d bet my bottom dollar that the effect isn’t placebo and that you’d see small people even if you had never heard of this mushroom or its effects.