Hearing and Hearing Aids-a Layman's Notions "

Consideration of hearing logically starts with the structure and function of the several parts of the human ear. The auditory portion of the brain, crucial though it is, must be taken for granted here. A chart of thresholds for different tones, the audiogram, not merely indicates normal or defective hearing of pure tones but provides important clues as to the nature and cause of a specific hearing loss. Tests sampling reactions to the more complex sound patterns used in speech are presumably more realistic yet more difficult to construct and interpret. Merely hearing the bursts of sound energy is not enough; the user must be able to understand and react meaningfully. An inappropriate response caused by an innocent misunderstanding can lead to ridicule or chaos. The hearing aid must amplify the sounds so they seem comfortably loud to the user but must not deliver an excessive maximum power output lest initially loud environmental noises become painfully loud to the user. Fidelity of amplification, though now substantially sacrificed to allow a dramatic degree of miniaturization, has an important effect on clarity of understanding of complex speech signals. One may suggest, too, that listening through a distorted system with poor transient response in serious background noise may cost the user both mental and physical fatigue. Initial physical tests of hearing aids as a screening measure, prescription of the most appropriate aid for an individual, and careful auditory training of the user (including instruction in. reading of lips and other facial gestures) are important steps in auditory rehabilitation.