Sensory deprivation lasting only 15 minutes is enough to trigger hallucinations in healthy members of the public, according to a new study published in the Journal of Nervous and Mental Disease.
The researchers were interested in resurrecting the somewhat uncontrolled research done in the 50s and 60s where participants were dunked into dark, silent, body temperature float tanks where they subsequently reported various unusual perceptions.
In this study the researchers screening a large number of healthy participants using a questionnaire that asks about hallucinatory experiences in everyday life. On the basis of this, they recruited two groups: one of ‘high’ hallucinators and another of ‘low’ hallucinators.
They then put the participants, one by one, in a dark anechoic chamber which shields all incoming sounds and deadens any noise made by the participant. The room had a ‘panic button’ to stop the experiment but apparently no-one needed to use it.
They asked participants to sit in the chamber for 15 minutes and then, immediately after, used a standard assessment to see whether they’d had an unusual experiences.
After a twenty minute break, they were asked again about perceptual distortions to see if there were any difference when normal sensation was restored.
Hallucinations, paranoid thoughts and low mood were reported more often after sensory deprivation for both groups but, interestingly, people already who had a tendency to have hallucinations in everyday life had a much greater level of perceptual distortion after leaving the chamber than the others.
This study complements research published in 2004 that found that visual hallucinations could be induced in healthy participants just by getting them to wear a blindfold for 96 hours.
However, my attention was grabbed by the researchers use of a ‘panic button’. The effect of having a panic button in sensory deprivation experiments was specifically studied in 1964 by psychologists Martin Orne and Karl Scheibe. They also asked about hallucinations and compared two groups of people.
One group was met by researchers in white coats, given a medical examination and told to press a ‘panic button’ if they wanted out. The other was met by researchers in causal clothes, weren’t given medical checks, and told to knock on the window if they wanted the experiment to stop.
The actual sensory deprivation part was the same, but the group with the panic button reported many more hallucinations, likely owing to ‘demand characteristics’, or, in other words, their expectations of what might happen.
We also know that an increase in anxiety also increases the likelihood of hallucinations, and having a ‘panic button’ during an experiment, I suspect, is likely put most people a little more on edge.
So we can’t be sure that the effect was purely due to sensory deprivation, but it does chime with various other studies showing that when we reduce our normal sensations, the brain has a tendency to ‘fill in’ with hallucinations.
Link to PubMed entry for sensory deprivation study.