Book T of C
Chap T of C
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In discussing visual perception we argued that hallucinations demonstrate the constructed nature of perception. Auditory perception is also an event constructed in the brain. Sound, like all integrated experience, must be synthesized (put together) by neural mechanisms. As with vision, the synthetic process does not always mirror the sensory information coming into the nervous system. Auditory hallucinations occur when the brain areas responsible for hearing music generate spontaneous activity. Older people who are going deaf in both ears sometimes hear musical hallucinations so vivid and realistic that they think it is coming from the environment.
A 75-year-old man came to the Boston Veterans Administration Outpatient Clinic on March 15, 1973, with a complaint of "hearing music in both ears." For 10 to 12 years the patient had experienced progressive bilateral hearing loss accompanied by sounds of hissing and buzzing. Three months before the outpatient visit he had noted the onset of hearing a soprano or baritone voice or a tenor and baritone voice singing familiar hymns and melodies. Many of the hymns he had previously sung in a church choir. In most instances the music was sung without words but occasionally he would hear part of the text that enabled him to remember forgotten verses. On rare occasions the melody was produced by an instrument, such as a cornet or clarinet.
The music usually began early in the morning and continued throughout the day with the same melody repeating itself innumerable times. The only control the patient had over the hallucinations was his ability to change the tunes by singing aloud or thinking about another melody. Sometimes the experience was so annoying that he would try to suppress it by playing a radio at extreme volume. At other times he enjoyed the musical hallucinations and actually sang along with them. (Ross, Jossman, Bell, Sabin, and Geschwind, 1975)
What do auditory hallucinations illustrate about the nature of auditory perception?
This phenomenon is evidently caused by spointaneous activity in auditory processing areas of the brain. A form of restlessness called disuse supersensitivity occurs when nerve cells are cut off from normal stimulation. In a lab animal such as a rat, disuse supersensitivity can be demonstrated by cutting around an island of cortex to isolate it from other brain tissue (but preserving the blood supply). Initially the isolated slab of cortex is silent, but soon it becomes irritable. It starts generating nerve impulses by itself. Perhaps something similar happens when old people go deaf in both ears. Normal sensory inputs from the environment are cut off, so the auditory cortex grows irritable and starts stimulating itself. The result is hallucinated sound.
Ross, Jossman, Bell, Sabin, and Geschwind found a second patient with the same problem: a "charming 83-year-old English woman" who three months earlier "noted the sudden onset of music in her right ear of such clarity and fidelity that she initially thought her radio was on...." Initially the music included choir hymns, but by the time she was discharged from the hospital, the musical hallucinations had changed to a "rock and roll variety."
What are examples of similar hallucinations involving other senses besides audition?
Similar activity, spontaneously generated, can occur in visual cortex. Charles Bonnet syndrome is named after a patient who saw hallucinations after losing sight in part of his visual field. Sometimes patients who lose vision in only part of the visual field will see hallucinations only in that area (Grady, 1993). Albertson (1984) noted that blind people frequently "see things" but usually do not discuss it for fear of being labeled insane.
The phenomenon of phantom limbs is similar. Phantom limbs are amputated limbs that feel like they are still present. This is a hallucination involving the kinesthetic sense (the sense of body parts and position). Tissue in the brain represented the body part is still present after the arm or leg is gone. The result is a hallucinated limb.
Sensory hallucinations can be elaborate and realistic. V. S. Ramachandra studied phantom sensations and their relationship to brain physiology. He told about one patient with a realistic phantom hand. When Ramachandra offered the man a cup of coffee, he "felt" it in his phantom hand. When Ramachandra pulled the cup away, the man complained that he felt it rip out of his hand (Shreeve, 1993). To read about cases of phantom limbs, see <http://www.macalester.edu/~psych/whathap/UBNRP/Phantom/casestudies.html>.
What is the point of all these examples?
These cases should remind us: one does not "hear" the sensory flow from the ears or "see" the nerve inputs from the eyes, or even "feel" the arm or leg in direct fashion. Rather, the brain uses sensory information to construct a sensory world. If the construction does not correspond to events in the outside world, we call it an illusion or hallucination. If the construction is accurate, we call it normal perception. But even normal perception is a construction in the brain.
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