human sonar hypothesis of auditory hallucinations

   The term human sonar is indebted to the acronym sonar, which stands for SOund NAvigation

   Ranging. The term sonar, introduced in 1963 by the Allied Submarine Detection Investigation Committee (ASDIC), denotes the echo-sounding technique developed under the Committee's auspices for the purpose of locating underwater objects with the aid of reflected ultrasonic sound waves. A similar - biological - mechanism is utilized by various species of animals, such as the bat, marmoset, mouse, oil bird, porpoise, rat, shrew, squirrel monkey, and whale. The human sonar hypothesis, put forward in 1952 by the American neurologist and psychiatrist Walter Jackson Freeman (1895-1972) and his colleague Jonathan M. Williams, suggests that "auditory hallucinations are mediated by a 'human sonar' system, tentatively embodied by the brain's amygdaloid nucleus. In the words of Freeman and Williams, "We erected the hypothesis that the amygdaloid nucleus transformed the ideational activities apparently mediated by the frontal lobe into complex temporally patterned movements of the vocal musculature and that the resulting effects were heard by the patient as voices coming from outside of himself - in other words, a form of human sonar." Conceptually, this version of the human sonar hypothesis comes close to the " subvocalization hypothesis, which suggests that " verbal auditory hallucinations can be mediated by subvocal speech produced by the larynx. The American neuroanatomist Fred H. Johnson elaborates on this hypothesis by suggesting that the sound waves involved are of a high frequency and that these may be perceived not only by the affected individual but also by others. To quote Johnson on this issue, "The sounds produced by the person who is hallucinating are sound vibrations far above the normal. They are acoustically of high-frequency waves of the upper partials of harmonics, which are an addition to the normal sound waves of the word as it is spoken aloud. These vibrations are in the ultrasonic range at times and would be inaudible to those who do not perceive hallucinations. The energy range for this type of sound wave is estimated at 100 db to 110 db, which is the level of a boiler factory. An echo evaluation of only 1/10,000 of that produced is needed for the perception of the sound. As a hypothesis one might think of these sounds as similar to those produced by a 'dog whistle,' which is above most human hearing range. Because these sounds are high frequency and very intense, they can be heard a long way as a result of the high energy... It is theorized that such vocalizations formed the evolutionary basis of communication." If we take Johnson's version of the human sonar hypothesis to its logical conclusion, this would apparently mean assuming that verbal auditory hallucinations may well be "veridical hallucinations, i.e. verbal auditory percepts caused by high-frequency sounds emanating from another person's larynx.

   References

   Freeman, W., Williams, J.M. (1952). Human sonar. The amygdaloid nucleus in relation to auditory hallucinations. Journal of Nervous and Mental Disease, 116, 456-461.

   Johnson, F.H. (1978). The anatomy of hallucinations. Chicago, IL: Nelson-Hall.