Rhode Island Medical News recently published an April fools article where the author joked about negative hallucinations, where someone didn‚Äôt see things that were really there, seemingly unaware that such hallucinations are in fact possible.
The article, which you can read online as a pdf, has various humorous references to jumping traffics lights or ignoring family members. But when I’m talking about the genuine version I don’t mean lapses of attention, blind spots, inattentional blindness or other momentary failure-to-notice effects. I’m talking about not seeing specific barn door obvious objects in your field of vision when you are concentrating on the area.
These are genuinely called negative hallucinations in the scientific literature although, as far as I know, they only occur in one specific context – after hypnosis.
In fact, the induction of a negative hallucination forms part of the Stanford Hypnotic Susceptibility Scale (Form C) although these sort of ‘anti-hallucinations’ are only experienced by the most hypnotisable of people – as are most ‘cognitive’ suggestions that effect the experience of your own mind (rather than changes in the sensation of control of movement, which most people can experience something of).
There is a small literature on ‘negative hallucinations’ with several studies examining changes in electrical activity from the brain (‘evoked potentials’) as the hallucination becomes active.
It’s still not clear how negative hallucinations work exactly. Almost all studies have found changes to attention, our ability to selectively process perceptual information, although the data is inconsistent largely owing to the small number of studies – a constant bugbear of hypnosis research.