What Are Hallucinations?

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Lanmaoa asiatica lacks psilocybin and ibotenic acid, yet it causes a hallucination of fantasy tiny people.

Lilliputian hallucinations appear across cultures and centuries with consistent, relatively similar features.

Brains construct perception through prediction, not pure sensory data, per neuroscience research.

Shared hallucinations challenge our assumption that collective experiences constitute verifiable reality.

For most people, the world around them appears certain and obvious beyond any doubt. We have sensory receptors that perceive information from the external world. However, the brain's perception of reality is not as simple as we think. The objects and events we face daily, even though they appear very real to us, might not be real at all. This time, not only philosophers but also neuroscientists are in consensus on this complexity. Modern neuroscience suggests that the brain uses sensory signals to make predictions about external information that favor our survival rather than fitting with reality. We can give many examples of errors in visual, auditory, and other sensory systems.

Lisa Feldman Barrett provides a compelling example at the opening of her book, Seven and a Half Lessons About the Brain. She says that a soldier in the civil wars of southern Africa, while doing drills in the forest, suddenly spots what appears to be a line of camouflaged fighters armed with AK-47s. His heart pounding, he raises his rifle and flips off the safety, until a comrade grabs his arm and says, "Don't shoot, it's just a boy." He looks again and sees a ten-year-old herding cows with a stick, not a rifle. The writer tells this story to show how predictive processing works: The soldier's brain had built a strong prior perception from past combat........

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