How Much Of What You See Is A Hallucination?

For most people it’s not much, but nobody’s immune, and Dr. Elizabeth Cox details several ways it can happen:

The Amazingly Deceptive Circus

One day, Rosalie had an interesting experience. Sitting alone at home, suddenly she was interrupted by a circus troupe entering the room, with elaborate scenes of animals, children, costumes, and swirling fabrics that appeared suddenly and felt as real as normal vision.

One thing that added an extra layer of interest is that she was completely blind.

This one’s called Charles Bonnet syndrome: people with severe vision loss or blindness can experience vivid, detailed visual hallucinations despite having normal cognition and knowing the images are not real. These episodes can last minutes or recur over many years, and researchers still do not know why they start, stop, or affect only some people.

Notably, Charles Bonnet develops only in people who had normal vision before losing it, suggesting the brain uses stored visual memories to compensate for the lack of new visual input.

Which makes sense, because for most people, when the brain receives little or no input from a sense, it may generate its own perceptions, making the brain’s usual “fill in the gaps” process (by which technically we are all hallucinating for several hours per day in total, just in fractions of a second a time, and also by which the brain additionally fills in the gap created by the blind spot where the optic nerve leaves the retina) much more obvious.

It is worth noting that fMRI studies show that hallucinations activate the same sensory brain regions used for real perception, and not the areas involved in imagination.

There are a lot of ways hallucinations can come about: sensory deprivation, epilepsy, narcolepsy, schizophrenia, and certain recreational or therapeutic drugs can all trigger hallucinations, and hallucinations are not only visual, for example people with impaired hearing may hallucinate voices, music, or even complex sounds such as an entire marching band.

For more on all of this plus how some drugs (such as LSD and psilocybin) do it, enjoy:

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Want to learn more?

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Take care!