Hallucinations in silence
I have been asked about recent claims that very quiet anechoic chambers can cause hallucinations. We have an ultra-silent anechoic chamber around the corner from my office as part of the Acoustic Labs at University of Salford.
In a very quiet anechoic chamber no sound from the outside world enters you ear canals. That does not mean, however, that you hear silence. You might hear the blood gently pumping through your head, or a high-pitched hiss caused by spontaneous firings of the auditory nerve. Normally, these internal sounds are masked by external noises and so are inaudible. If you have tinnitus (ringing in the ears), then it becomes very obvious in an anechoic chamber. But none of these effects are hallucinations. In the 20+ years I’ve been at Salford I’ve never heard of anyone claiming to have suffered hallucinations.
Stories claiming that anechoic chambers cause hallucinations in 15 minutes were prompted by a study by Mason and Brady . They placed people in a completely dark and silent space for 15 minutes. Some test subjects were very susceptible to hallucinations and they saw “objects that were not there, five had hallucinations of faces, four reported a heightened sense of smell, and two felt there was an evil presence in the chamber with them.”  Mason and Brady also tested less susceptible individuals who had fewer hallucinations. However, Vaughan Bell has questioned whether the experimental method rather than the silence caused hallucinations through heightened anxiety.
I’ve never tried sitting in complete darkness in our anechoic chamber, but I have been in a flotation tank. These are silent, and pitch-black and look like a large meat safe. You float in the nude in brine at body temperature. I did this as part of research for The Sound Book (coming out in 2014). During the two hours floating in the tank, the weirdest sensation I got was the feeling that my hands and feet were detached from me because I couldn’t feel my arms or legs. That is the closest I got to a hallucination.
Hallucinations or not, visiting the anechoic chamber is strange and unnerving experience. We are hoping to open the chamber for public tours for one day during the Manchester Science festival 2013.
Have you had hallucinations in an anechoic? If yes, tell me of your experience below
 Journal of Nervous and Mental Disease, The psychotomimetic effects of short-term sensory deprivation, Mason OJ, Brady F.; 197(10):783-5