Hallucinating the void

Rhode Island Medical News recently published an April fools article where the author joked about negative hallucinations, where someone didn’t 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.

Link to April fools article PubMed entry.
pdf of full-text
Link to Google Scholar search of negative hallucination studies.
Link to PubMed search of negative hallucination studies.

3 Comments

  1. Daniel J. Simons
    Posted May 25, 2010 at 2:41 am | Permalink

    Always fun when parodies become reality. That’s similar in some respects to the Onion piece on gorillas becoming aware of their own mortality followed a week later by actual research on chimps acting as if they understood the death of other chimps.
    I think you have slightly mischaracterized inattentional blindness in your description, though. In cases of inattentional blindness, people are missing the proverbial barn door right where they are looking. In fact, Daniel Memmert has shown that people can miss the “gorilla” even when looking right at it. The key difference between inattentional blindness and the sort of negative hallucination you describe (that I had never heard of before) is that in inattentional blindness, your not looking for the barn door. Instead, attention is focused on something else in the same part of the display. In fact, Neisser’s earlier work was designed to show that people would miss something right where they were looking.
    Maybe negative hallucinations are like an induced or suggested form of inattentional blindness in which attention is diverted by suggestion rather than due to the need to focus on some other task.

  2. Posted May 25, 2010 at 6:58 am | Permalink

    This is interesting. I had never heard of inattentional blindness. Any idea why such a thing would be used, other than for fun?
    Hypnosis has some good uses per personal improvement, I have to wonder if there is something to this.

  3. Posted May 25, 2010 at 5:11 pm | Permalink

    My understanding is that through hypnosis, and by other methods, one can suppress activity in certain areas of the brain. For example if the suggestion is made that the subject cannot read then the part of their brain that processes written letters is some how made inactive. There are a few hypnosis studies that had subjects turn synthesia on and off.


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