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On Thursday, it was extremely satisfying to discover the answer to a question I have heard posed repetitively throughout my life. When a tree falls in the forest, we said, it sets off vibrations. There is no sound unless a nervous system is there to perceive those vibrations and thus those sounds. However, although I am able to understand this concept, and its relationship to vision, this realization has forced me to question other ideas that I have previously taken for granted.

For example, I wondered about people who hear voices or have visual hallucinations. Although “hearing voices” and “seeing things” have been generally thought of as signals of mental illness, could incorporating our understanding of the tree in the forest shed light on these types of situations?

If an individual’s nervous system hears or sees something, are other individuals really able to be certain that nothing made a noise or presented an image?
If an individual hears a noise or sees an image, then hasn’t a noise been made or an image been shown? In the New York Times this week I read that one survey concluded that 39 percent of healthy volunteers said they have heard their own thoughts out loud in the past. If an individual’s nervous system perceives a sound or image, then isn’t it valid? Are other individuals really able to question the validity of a peer’s perception?