What every otolaryngologist should know about hearing aids.

The otolaryngologist does not have to fit hearing aids, but he does have to know with a broad encompassing view what is being done by the hearing aid dispenser and the audiologist in regards to hearing aid fitting and selection. The acquisition of a hearing aid is part of the general care for the hard of hearing. In this particular case, the otolaryngologist should always be the "Captain of the Ship." With him, as paramedical advisors and assistors, are the audiologist and the hearing aid dispenser. The ultimate responsibility of the members of this team to see that the patient is properly fitted and cared for is with the otolaryngologist. When problems exist with improper diagnosis or care, the medical-legal responsibility falls on the shoulders of the otolaryngologist. Having an audiologist work with the otolaryngologist is most desirable for the measurement and recommendations for the hearing aid. The new FDA regulations require an otolaryngologic examination prior to fitting hearing aids, except for personal and religious reasons. Children under 18 years of age require both a medical and audiologic examination. To simplify conversation with other members of this team, one should have some basic concepts clarified: 1) The nature of a hearing aid. 2) The concepts and nomenclature used in and for probably 90% of all descriptions regarding hearing aids. 3) Types of aids. 4) Coupling methods which involve ear molds, tubes, vents, and inserts. 5) Types of fittings, whether cross, bi-cross, monaural, etc. 6) Distortion. 7) Measurements. 8) Problems in fitting of hearing aids. It is reasonable to assume that adequate background in these simple basic concepts regarding hearing aids will permit the otolaryngologist to supervise and understand the nature of some of the complaints made by patients. It is totally desirable that a patient be seen by an otolaryngologist prior to being fit with a hearing aid. This can be accomplished by education of the public by the otolaryngologist.

Earmold configuration: relation to speech discrimination scores.

Choice of the earmold for a particular individual is perhaps the most subjective of all decisions made by clinicians in hearing aid fitting. The four earmold designs used in this study were standard-long, standard-short, belled-vented, and cavernous. Conslusions were: 1) performance differences in earmolds of contrasting design can be assessed by discrimination scores with monosyllabic word lists of equal difficulty; 2) among the physical measures taken of the earmold-receiver systems, frequency-response overall range (HAIC) ranked the devices in agreement with group responses to a word identification task; and 3) these data offer a basis for endorsement of the standard-long and cavernous-short earmold types over the other two with their superiority evident in each of the discrimination categories of excellent, good, and poor.

Frequency responses of hearing aids and their effects on the speech perception of hearing-impaired subjects.

Eight hearing-impaired subjects were tested with a binaural master hearing aid. This aid has "on-the-head" miniature transducers and has an adjustable frequency response. Five frequency responses were used, two of them were defined by their response in a 2-cm3 coupler: 1) uniform coupler gain (UCG), and 2) 6 dB per rise (6 dB). The other responses were defined in terms of functional gain (difference between unaided and aided thresholds): 3) uniform functional gain (UFG); 4 uniform hearing level (UHL); and 5) a simulation of a commercial hearing aid (AS). A significant difference between coupler and functional gain was seen. Discrimination was tested with a special closed-set word list which includes fifty monosyllabic words with a high percentage of voiceless phonemes. Discrimination scores were consistently better with the UHL response. The lowest scores were obtained with the AS response. The average difference in scores between these two responses was 18.4%. Further testing replicated these results and also compared the effects of a different type of word list phonetically balanced (PB); with these lists, the above-mentioned difference in scores was smaller in quiet (5.9%) but larger in noise (20.9%).

Review of recent research on the selection of frequency-gain characteristics for hearing aids.

Following the Harvard master hearing aid study in 1947 there was little research on linear amplification. Recently, however, there have been a number of studies designed to determine the relationship between the frequency-gain characteristic of a hearing aid and speech intelligibility for persons with sensorineural hearing loss. These studies have demonstrated that a frequency-gain characteristic that rises at a rate of 6 dB/octave, as suggested by the Harvard study, is not optimal. They have also demonstrated that high-frequency emphasis of 10-40 dB above 500-1000 Hz is beneficial. Most importantly, they have demonstrated that hearing aids as they are presently being fit do not provide maximum speech intelligibility. Percent word correct scores obtained with the best frequency-gain characteristics tested in various studies have been found to be 9 to 19 percentage points higher than scores obtained with commercial aids owned by subjects. This increase in scores is equivalent to an increase in signal-to-noise ratio of 10 to 20 dB. This is a significant increase which could allow impaired listeners to communicate in many situations where they presently cannot. These results demonstrate the need for further research on linear amplification aimed at developing practical suggestions for fitting hearing aids.

Uses and abuses of hearing aids.

The view is expressed that many hearing-impaired individuals are not deriving maximum benefit from amplification or are not using amplification at all because of failure of professionals to keep in mind certain uses and abuses. Some of the specific uses are for minimal and profound hearing losses, adaptation with special earmold modifications, chronic or recurrent conductive losses, part-time use, and binaural listening. Some specific abuses include: unrealistic expectations, overlooking the role of motivation, pressuring persons to try/wear amplification, overamplification, Y cord, inappropriate binaural fittings, and failure to alternate a hearing aid between ears in symmetrical hearing losses.

A multiple electrode cochlear implant.

The University of Melbourne Departments of Otolaryngology and Electrical Engineering (UMDOLEE) receiving and stimulating component of a multiple-electrode cochlear implant hearing prosthesis produces constant stimulation. It has a stimulating pulse shape that minimizes the production of toxic substances and loss of metal from the electrodes, and this is achieved with a biphasic rectangular waveform where the first phase is negative with respect to ground. The duration of each stimulus phase in 180 msec, which is long enough to allow low levels of current stimulation, and short enough to permit rates of 1000 pulses/second to be achieved. In order to be consistent with our present understanding of the perception of pitch, the device permits the independent stimulation of a number of electrodes. Furthermore, to electrically isolate the stimulus to small areas, there is the capacity to vary the current and set the threshold independently at individual electrodes. The phase and amplitude of the pulses to neighbouring electrodes with also be varied to assist in localizing the current flow. The pattern to stimulation to individual or groups of electrodes can also be altered to enable studies to be carried out to determine ways of conveying frequency and intensity information over a more normal dynamic range.

Frequency shaping and multiband compression in hearing aids.

Compression and noncompression amplification were compared for a range of conditions. The noncompression conditions included flat-frequency response and "LDL frequency response," with and without peak clipping. The compression conditions included a single-band compression system and two combinations of a two-channel compression system. The LDL frequency response was obtained by finding the LDL for each subject using one-third octave bands of noise and then determining that frequency response which would amplify each one-third octave band of speech to just below the LDL for that band. A low-frequency roll off below 300 Hz was used to reduce upward spread of masking. Four hearing-impaired persons served as subjects. Four replications of the Nonsense Syllable Test were administered in quiet and in noise for each experimental condition. The highest scores were obtained, on the average, for the condition of noncompression, no peak clipping, with the LDL frequency response. There were, however, large individual differences in relative performance on different conditions, indicating the importance of individualized determination of optimum amplification characteristics.

Amplification for hearing-impaired children: basic considerations.

The importance of the selection of proper amplification for the hearing impaired child is discussed including goals of amplification, specific methods of choosing amplification, and test procedures including speech audiometry. Evaluation controversies discussed include: monaural versus binaural amplification; body worn versus post auricular hearing aids; maximum output; and special hearing aid modifications.

Communication systems for deaf people: a review of possibilities.

This article reviews the possibilities for communication in deaf people. The various types of deafness are categorised and their associated problems briefly discussed. Communication aids are then described in greater detail in terms of the three possible modes of transmission and reception: speech, the written word and coded signals.

Sensory substitution and the design of an artificial ear.

This paper is concerned with attempts at sensory substitution and in particular with devices that have been designed to substitute for hearing by using the skin as an alternative channel of communication. A review of the literature suggests that the failure or limitations of tactile substitution systems are due, not to the inadequacy of the skin's perceptual processing capacity, but to inappropriate displays, ineffective training methods, or insensitive testing techniques. Specifically, displays have been artificial in that they have typically failed to preserve the information relevant to the modality for which they are supposed to substitute. Furthermore, certain false assumptions and misconceptions have been manifest in testing techniques which have not taken into account the way in which perceptual processes normally develop and operate. The result has been that some important evidence has been ignored or has gone unnoticed and that some promising devices have been prematurely abandoned. In the final section of the review, some suggestions are made concerning the design, application, and evaluation of an artificial ear.

[Simulator for individual auditory training of hard-of-hearing persons]. / Trenazher dlia individual'noi slukhovoi trenirovki lits s tugoukhost'iu.

A device-trainer intended for individual exercises with patients suffering from an intensively pronounced hearing defect is described. The device permits it to reproduce sound signals amplifying them up to 130 dB in the mono-binaural and also in the stereophonic modes and provides for a wide bandwidth. The originals can be presented by using the auditory and vibro-tactile reception.