over, what may be called the "annoyance factor" of sounds is greater at higher frequencies. A person who has for years suffered a progressive loss of high-frequency hearing is therefore likely to find his first experience with a hearing aid somewhat dismaying. If it will enable him to comprehend speech, he will also rediscover the squeaks and clatter previously screened from him by his own diminished hearing. Almost any one inured to the semisilence of hearing loss may require some time to become readapted to loud sounds. Sensitive individuals may need several months or more to become accustomed to fuller hearing. Eventually most users of hearing aids come to overlook the inevitable noises for the sake of hearing speech with ease. There are several tests that an individual can use to assist him in deciding whether he is getting the most help from his hearing aid. An inexact but very practical method for finding out how it behaves is to make an articulation test. An articulation test is based upon the idea that the primary purpose of a hearing aid is the communication of speech. It is simply a refined method for talking to a subject and determining how much of the speech he can understand. Because understanding is involved, ordinary words common to everyone's daily life must be used. An attempt is made to choose words that represent a good sample of the sounds that make up speech. A set of such word lists, the PB or "phonetically balanced" word lists, has been developed at the PsychoAcoustic Laboratory of Harvard University. Two of these PB word lists are given in Table 1. One list suffices for a single test, but smaller parts of a single list will not be adequate, because all the speech sounds will not be tested in their proper ratio. To avoid the effects of memory, the words should be copied on cards so that they can be presented in random order. A person who is trying out a hearing aid should get a friend to make this test with him. He should not face the reader, in order that lip reading will not affect the result. The most favorable position is for the reader to be diagonally at one side from the listener so that his face is just removed from the listener's direct line of sight. Interposition of any large obstacle between the reader and the microphone of the listener's instrument should be avoided in the test. The presentation of the words should be done carefully. To present them naturally, they should be spoken in a sentence in a normal conversational tone. The sentence must be chosen so that the test words cannot be inferred from the rest of the sentence. A carrier sentence commonly used is "You will say * * * now. This sentence has the advantage that the "a" sound in "say" is a high-level sound and can be used by the speaker for checking on his voice level. The sentence should be spoken at ordinary conversational level. It is unlikely that the person making the test will get 100 percent of the words correctly. Even under ideal communication conditions (with two persons in the same quiet room, but not facing each other) the random word articulation scores are usually 95 percent. Apparently, individuals with normal hearing actually judge the remaining 5 percent of the words in ordinary conversation by familiarity, context, or lip reading. By noticing the particular speech sounds that are missed by the listener in writing down the word list, and comparing them with the chart in figure 2, it is possible to get some idea of the particular way in which the hearing aid fails to compensate for hearing loss. Perhaps the simplest way for determining whether a hearing aid has a resonance is to listen to footsteps or a typewriter and notice whether a particular note seems to be favored. If there is access to a piano, the resonance can be found by having someone play through the keyboard range several times with a uniform touch. If the hearing aid gain is uneven, certain notes will sound markedly louder or softer than the rest. Experimentation shows that peaks can be detected in this way if they are greater than 20 decibels in magnitude. In general, the presence of competing noise is a critical test of the performance of hearing aids. Problems with overload and resonance become strikingly evident when noise is present to be mixed with the speech. You should try your prospective hearing aid under noisy conditions as well as in the quiet. Occasionally you may find a hearing aid that picks up hum from power systems and fluorescent lights. Even though you may have no fluorescent lights in your house, they often are used in restaurants and stores. This form of pickup is strongly directional; if you suspect it is giving trouble, you can try turning the hearing aid. Usually, with hum pickup, you can find a position in which the hum is at a minimum. Most modern hearing aids are designed to avoid this trouble. In many hearing aids, especially those designed for higher amplification, the ability to pick up a stray magnetic field is used as a virtue; a special pickup coil is connected so that it may be switched into the amplifier as a substitute for the microphone, and it may be used in place of the microphone to pick up the signal from a telephone receiver. Since it works only on the magnetic field of the receiver, it cuts down markedly on the room noise reaching the hearing aid. Many high-gain hearing aids contain this feature, and you may want to try it. 5. Guidance in Choosing a Hearing Aid The first step in overcoming loss of hearing is to determine whether the condition responsible for the loss can be remedied or at least checked in its progress by medical treatment. Some causes of conductive loss can be remedied by surgery. The nature of the hearing loss should be found in order to know whether the loss can be compensated by a hearing aid. For the answers to these questions a physician, preferably an ear specialist, should be consulted. If medical examination indicates that a hearing aid will be helpful, the next problem is the selection of the instrument. Numerous makes are on the market, offering a wide variety of choices. Most manufacturers offer two or more models. Some dealers undertake to provide assistance in the selection of a particular model (from among their own instruments) by methods more or less similar to those outlined in the previous section. A person shopping for a hearing aid may find it helpful to take with him a person with normal hearing so that, as he tries out different instruments, he may listen to words spoken by the same person. The prospective user should if possible try out one or more hearing aids in his own ordinary surroundings. Some companies provide a trial plan, occasionally charging a nominal rental that may be applied to the price of the instrument if it is purchased. Hearing aids are designed to be worn as inconspicuously as possible. For people with mild and moderate losses, instruments may be made so small that they can be worn on the head in some way. They are sometimes concealed in the frames of spectacles, with only a plastic tube leading from the earphone to the earmold. (This may make it inconvenient to wipe the lenses because it becomes necessary to detach the hearing aid from the ear.) Over-the-ear hearing aids are very commonly used, and have the advantage of being inconspicuous, without being bound to the eyeglasses. For mild losses, a small hearing aid can be built directly into an earmold. These head-worn aids have certain acoustical advantages. There is no clothing noise produced. The instrument is not muffled by clothing, and the listener can rotate his head to receive the best sound, just as he could if he were not wearing a hearing aid. Some compromises in sound quality must be made because of the small size of these types of hearing aids. The use of plastic tubing to conduct sound to the ear produces an irregular frequency response characteristic. However, the good points of head-worn hearing aids make them worth consideration by many people. If the hearing loss is severe, a body-worn hearing aid is necessary. The better sound quality that is possible because of the external earphone and larger size often makes them desirable for other degrees of loss, also. Elderly persons find them easier to operate than a head-worn aid. When comparing a body-type aid with a head type, the body instrument should be placed in the pocket or under the clothing, just as it will be in actual use. Some persons are made self-conscious by the visibility of their hearing aids. However, some users report that the hearing aid is helpful even when it is not turned on. Conscientious speakers tend to be more careful of their diction when reminded that a communication problem exists. In any case, when a person is observed to take part in a conversation with ease, few persons continue to be aware of how the process is achieved, just as many of us are not sure of which of our friends wear eye glasses. If you wish to obtain the best possible hearing, make your selection on the basis of performance and not merely on cosmetic appeal. However, do consider that the hearing aid is worn continuously for a long time, and consider how comfortable it feels. A convenient pocket-sized pamphlet "Choosing a Hearing Aid" has been published by the Children's Bureau, U. S. Department of Health, Education and Welfare. It is listed as Children's Bureau Folder No. 55-1965 and can be purchased from the Superintendent of Documents, U. S. Government Printing Office, Washington, D. C. 20402. The price is 15 cents (stamps not accepted). You may find it useful to carry with you as a pocket memorandum. After the hearing aid is selected, there is often the problem of indoctrination and of learning to make the best use of the hearing aid. This problem may be severe if the user has waited so long before purchasing a hearing aid that he has begun to forget what voices and noises really sound like and how noisy the world. is. Also he may have waited until he is too old to learn readily how to adapt himself to a new device. The quality of speech heard through a hearing aid may differ from that to which he has become accustomed. The transition may be considerably helped by wearing the instrument for only an hour or two each day at first and by some systematic "auditory training" or practice in listening. To assist the hard of hearing in some of these problems a number of "hearing centers" have been established throughout the country. Most of them are nonprofit civic enterprises under the auspices of local universities or hospitals; frequently a nominal fee for their services is charged to those who can pay it. These centers provide a variety of services, including in many cases advice on the selection of hearing aids. Practically all of them give hearing tests. Many offer otological examination by an ear specialist, and the majority provide other forms of assistance such as auditory training, lip reading, speech training, and vocational counseling. The hearing centers that offer demonstrations of hearing aids give prospective users an opportunity to try the types they have. Manufacturers are invited to submit instruments representing their current models, and although not all manufacturers are represented a wide variety of makes is usually available. This program has been assisted by a number of manufacturers and dealers who have supplied hearing aids voluntarily to the hearing centers. Partly because hearing centers cannot provide samples of all makes of hearing aids, they cannot be sure of guiding a person to the hearing aid best suited for him, but can give him a general idea of the compensation provided by hearing aids of various types. The centers do not sell hearing aids; an individual goes to commercial sources of supply to purchase his own instrument. The Professional Services Board of the American Boards of Examiners in Speech Pathology and Audiology registers clinical facilities which meet minimum professional standards in this field. A list of registered clinical facilities, as well as the criteria used in their evaluation, may be obtained by writing to the American Boards of Examiners in Speech Pathology and Audiology, 9030 Old Georgetown Road, Washington, D. C. 20014. For convenience, a partial list of clinical services is contained in appendix II. 6. Care of a Hearing Aid A hearing aid is somewhat different from other devices that a person uses in his daily life, and a small amount of special care in handling it may pay substantial dividends in increased usefulness and better performance. The sensitive element in some amplifiers is injured by exposure to high temperatures, and will be ruined permanently by temperatures above 120°F. Such temperatures may be produced locally if the aid is left lying in the sun, in a closed parked car, or too near a radiator. In several instruments these components are made of special high-temperature materials. However, batteries also deteriorate more rapidly at elevated temperatures. For such reasons, it is well to protect aids from extremes of temperature. The electrolyte in the batteries is either a moderately strong acid or a strong alkali and may cause damage if the battery cases leak. This is likely to happen when the battery is run down. For this reason, it is advisable to separate the battery from the instrument when it is not being worn, especially if the battery is mounted in the amplifier case. Since the battery case is consumed in the chemical process that produces electricity in the battery, usually it is not practical to recharge the batteries. Although this is suggested sometimes as an economy measure, the probability of leakage or bursting is greatly increased because the case material is not renewed by recharging. There are some cells on the market designed for recharging. They are true storage batteries and are usually somewhat more expensive on initial purchase than dry-cell batteries. Rechargeable nickel-cadmium cells are available in sizes that fit ordinary dry-cell mountings. Their life per discharge is approximately one-third that of a drycell but they are rechargeable for a large number of cycles. The Bureau acknowledged "the assistance and suggestions provided by the National Research Council's Committee on Hearing, the Volta Bureau, the American Hearing Society, the Audiology and Speech Correction Center at Walter Reed Hospital, and many interested individuals" in the Preface to Circular 516. Again, we are indebted to our many friends, among whom we should like to mention: the American Speech and Hearing Association, the Alexander Graham Bell Association for the Deaf, the National Association of Hearing and Speech Agencies (formerly the American Hearing Society), and the Committee on Hearing and Bioacoustics of the National Academy of Sciences. 7. Appendix I The committee on Conservation of Hearing of the American Academy of Ophthalmology and Otolaryngology recommends the division of the handicap of hearing into classes or grades, according to the accompanying table. The over-all handicap of impaired hearing is best estimated in terms of ability to hear everyday speech well enough to understand it, but for statistical purposes the more precise measurements of pure-tone audiometry are preferable. Each class shown in table 2 is defined in terms of the average hearing threshold level for three audiometric frequencies that are important for the understanding of speech. Editor's Note: The symbol ISO stands for the threshold standards set by the International Standards Organization. These correspond to somewhat more acute hearing as a norm than do the standards of normal threshold of hearing previously current in the United States. For audiometers standardized against the older U.S. standards (often abbreviated ASA for the American Standards Association), the corresponding hearing loss levels are approximately 10 dB less at frequencies of 500, 1000, and 2000 Hz. An example of this situation is as follows: A person whose hearing threshold averaged for the frequencies 500, 1000, and 2000 Hz is 50 db (ASA) would have the same degree of hearing loss as a person whose hearing loss was 60 dB (ISO). To translate the categories listed in this table for the audiograms obtained with instruments adjusted to the older ASA standards, subtract 10 dB from each of the category boundaries. (The standards have changed; the diagnosis has not.) Ultimately, it is expected that audiometers will be referred to the ISO norms, but at present the changeover is not near completion. *Whenever the average for the poorer ear is 25 dB or more greater than that of the better ear in this frequency range, 5 dB are added to the average for the better ear. This adjusted average determines the degree and class of handicap. For example, if a person's average hearing threshold level for 500, 1000, and 2000 Hz is 37 dB in one ear and 62 dB or more in the other his adjusted average hearing threshold level is 42 dB and his handicap is Class C instead of Class B. Appendix II. Hearing Centers The following list of hearing centers has been compiled from a current list supplied by the National Association of Hearing and Speech Agencies, supplemented by our own correspondence. This list is of necessity incomplete, but it is included as an aid to the reader. The American Speech and Hearing Association publishes a list of more than 900 sources of speech and hearing clinical services in a "Guide to Clinical Services in Speech Pathology and Audiology." A copy of this Guide may be obtained by writing to the American Speech and Hearing Association, 9030 Old Georgetown Road, Washington, D. C. 20014. Other lists of facilities may be obtained from the Volta Bureau, 1537 35th Street, N.W., Washington, D. C. 20007, The National Society for Crippled Children and Adults, 2023 West Ogden Avenue, Chicago, Illinois 60612, and the National Association of Hearing and Speech Agencies, 919 18th Street, N.W., Washington, D. C. 20006. The Veterans Administration maintains, at present, a testing program for use in purchase of hearing aids. The tests cover a relatively limited range of instruments. However, if an instrument you are considering for selection happens to be included in the VA program, you may be able to make use of its annual report. The 1970 issue is priced $2.50, available from the Superintendent of Documents, U.S. Government Printing Office. It is titled "Hearing Aid Performance Measurement Data and Hearing Aid Selection Procedures, Contract Year 1970." ALABAMA Speech and Hearing Clinic Auburn University Medical College of Alabama 1919 7th Avenue, S. Birmingham, Alabama 35233 Speech and Hearing Department Speech and Audiology Department Speech and Hearing Clinic 306 Oak Street Montevallo, Alabama 35115 Central Alabama Rehabilitation Center Northeast Alabama Rehabilitation Center Muscle Shoals City, Alabama 35662 Alabama Institute for Deaf & Blind 205 East South Street Talladega, Alabama 35160 |