The role of the audiologist in aural rehabilitation services on behalf of older adults with hearing impairment is expanding, just as our knowledge of hearing in aging likewise expands . In the past, audiologists generally found that they could not do as much as they desired to assist their older patients in acoustic design modifications to alleviate or prevent environmental interference in communication. This was, in part, probably a result of a lack of academic preparation in the area of environmental design. Training in that area has, in most instances, not been generally available in the majority of preparatory programs. This lack of information has restricted audiology students from learning about an important service that can improve the communicative efficiency of many older adults with impaired hearing function.
Rather than letting colleagues continue to rely on a "seat of the pants" approach to environmental design, this editorial will introduce the concepts and principles of environmental design that take into account aspects of hearing impairment in older adults, including design concepts and the physiological bases for those design considerations.
AUDITORY CHANGES IN AGING
The complexities involved in the peripheral and central nervous system (CNS) auditory components of presbycusis, along with the compounding effects of the auditory environment, can negatively influence an older adult's ability to communicate in their frequented listening environments. Many public and private listening environments play havoc with aging peripheral and CNS auditory systems. Adults who, at an earlier age, may have noted only some difficulty in specific degraded listening environments may now be experiencing frustrating difficulty. They may blame the difficulties on the speaker, when the problem might be the reverberant characteristics of the meeting room, the anechoic environment of their home, or auditory distractions. These older adults with hearing impairment might begin to avoid places where they would otherwise like to be, increasing their social isolation. Changes in both the peripheral and CNS auditory systems can occur in conjunction with advancing age. The following classic example presents a concise summary of the insidiousness of those changes:
"Unlike Dr. Oliver Wendell Holmes' New England Deacon who built the wonderful one-horse shay, the architect of the cochlea did not design it to give perfect service for 'a hundred years to a day,' or even for the traditional three-score-and-ten. Its condition in old age, however, seldom represents the effects of aging alone, but rather the accumulative, combined assaults of noise and drugs, as well as time." [2, p. 139]
Many older adults experience a gradual decline in the CNS auditory system's ability to process the acoustic complexities of speech with the speed and accuracy that they possessed in their younger years. If the slightest decline in speed and precision at the level of the brain stem and/or auditory cortex needed to process the acoustic and linguistic components of speech is noted and if that decline in speed of processing is coupled with a peripheral hearing loss in the higher frequency phonemes of speech, which is typical of older adults, then the difficulties that they can experience in hearing and understanding speech will be compounded.
Peripheral Auditory System
The peripheral auditory system's functioning declines regularly over time. A person's lifestyle, noise exposure, heredity, diet, state of cardiovascular health, and other variables can result in some degree of negative change within the cochlea, with an accompanying sensorineural hearing loss--a gradually progressive sensorineural hearing loss that typically involves the higher frequencies. Since approximately two-thirds of American English phonemes possess important high-frequency acoustic components, a hearing loss that primarily involves a decline in the higher frequencies can negatively affect speech understanding. …