Use of post-aural aids by National Health Service patients.

The amount of use made of post-aural aids issued through the National Health Service was investigated by monitoring the discharge rate of zinc air cells supplied to two matched groups of patients. Each group consisted of 36 subjects, the first group received an aid in the normal routine manner but without any extra counselling. The second group received both pre- and post-issue counselling. Subjective reports for the patients on use showed some degree of exaggeration, though not as much as was seen in a previous study of users of body-worn aids. Use was substantially greater with the head-worn aids than with the body-worn models previously supplied through the NHS. Use has at least doubled on average and the percentage of non-users has fallen. Counselling (as provided through the Manchester Scheme) appears to effect a significant reduction in the percentage of non-users regardless of the type of aid supplied. Use among those receiving counselling is significantly greater than in those not so being helped. Use tends to diminish with increasing age of the subjects on application for assistance. It tends to increase over the first year of use, but the rate of change is dependent on many factors. In this study, no relationship was found between hearing-aid use and hearing loss, but this may be due to the rather close clustering of hearing losses of subjects under consideration. No relationship was found between use and living circumstances (alone or with family, etc.) but this is more likely to reflect the weakness of the measurement tool than any real differences. No relationship was found between use and stated duration of hearing loss or across the sexes. The zinc air cell proved to be a very satisfactory method of assessing use, and could be used for initial assessment of use in newly issued patients to identify those making poor use of the aid who might be in need of counselling or other forms of assistance.

A modified polymer foam earplug for the hearing aid evaluation.

Functional gain was compared with 12 subjects using three earmold conditions: an E-A-R polymer foam earplug modified for use with a hearing aid, a personal custom earmold, and a best-fit receiver-type stock earmold. Functional gain was equivalent between the modified E-A-R earplug and the custom earmold conditions. The stock earmold condition resulted in a significant shunting of low-frequency amplification. The gain control of the personal hearing aids could be adjusted to the user comfort level gain setting without resulting in acoustic feedback in only the modified E-A-R earplug and custom earmold conditions. These findings are discussed relative to the hearing aid evaluation.

Study of multichannel amplitude compression and linear amplification for persons with sensorineural hearing loss.

Experiments were conducted on five listeners with sensorineural hearing impairments using two 16-channel, computer-controlled, amplitude compression systems, and four linear systems. One of the compression systems was designed to restore normal equal loudness contours, the other employed reduced high-frequency emphasis and reduced compression ratios. The linear systems differed only in their frequency-gain characteristics (orthotelephonic plus three characteristics with high-frequency emphasis that were expected to produce better results than orthotelephonic). In the main experiment, all systems were compared for each listener using nonsense CVC monosyllables and sentence materials spoken by male and female talkers and presented in quiet/anechoic and noisy/reverberant environments at the most comfortable level for each listener. The linear systems with high-frequency emphasis performed substantially better than the orthotelephonic system. Performance with compression was generally slightly worse than with linear amplification. Compression was superior to linear amplification only when speech materials with significant item-to-item level variation were used in quiet with subjects with more severe losses and when reduced input speech levels were used. To the extent that these two conditions represent real-life communication conditions, these results suggest that compression is preferable to linear amplification in a wearable hearing aid.

Earmold options for wideband hearing aids.

A summary of recent developments in earmold constructions for wideband hearing aids is presented. Earmold modification techniques, special earmolds, and temporary earmolds are discussed. The appendix contains the results from transmission line theory as applied to earmold acoustics and some sources for useful earmold supplies.

A new computerized method for hearing aid fitting based on measurements at the ear drum.

A computerized system is described for measuring a hearing aid's etymotic frequency characteristic on patients. A small-scale clinical investigation using this equipment showed that rather large differences can be found between a hearing aid's frequency characteristic as measured according to IEC 118 (using a 2 cc coupler) and the etymotic frequency characteristic as measured by probe microphone at the ear drum. The investigation shows that in practice it is difficult to optimize the etymotic frequency characteristic by modifying the hearing aid and the ear mould. Measurements of the etymotic frequency characteristic using several different hearing aids, but with the same ear mould on the same test subject showed only limited variation in the upper limiting frequency.

Use and benefit of postaural aid in sensory hearing loss.

A sample of postaural hearing aid users was followed through adaptation to use of an aid over an 18-month period subsequent to issue. Minor assistance and advice was given but no intensive hearing therapy or other instruction. A miniature timing device was installed in an aid substituted for a few days to provide a check on self-reported extent of use. On both objective and self-report measures, postaural aids receive substantially greater use than the body-worn aids in comparable previous investigations, about half the aids being used over 4 hours per day. Word-identification of free-field listening in aided and unaided conditions showed advantages of 10% or more in only 45% of those tested, yet questionnaire responses suggested reliable subjective benefits in specific listening situations. The results justify taking not only measures of speech identification improvement but also questionnaire measures and measures of time of use in field trials when evaluating overall effectiveness of aid provision.

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.

A study of private hearing aid users in London.

A pilot study of 40 hearing aid users sampled directly from private hearing aid dispensers' records is described. Some comparisons are made between this sample and (a) 37 private hearing aid users who had sought help from the RNID Hearing Aid Advisory Service, and (b) 58 NHS hearing aid clinic patients who also possessed a private hearing aid. The main objective was to discover people's reasons for buying a hearing aid rather than obtaining one free of charge from the NHS. The reasons given were found to be mainly those of range of design and choice of hearing aids in addition to some advantages in the type of service offered by private hearing aid dispensers.

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.

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.

An influence of binaural hearing aids on positioning of sound images.

An influence of binaural hearing aids on positioning of sound images produced by signals from two loudspeakers was investigated with normally hearing and hearing-impaired subjects. The image can be positioned along a horizontal line connecting the centers of the sources by adjusting the relative sound pressure levels of signals. When the listener is a symmetrical receiver, the image appears on the midline (0 degrees azimuth) for equal levels or away from the midline for unequal levels. Any asymmetry of the receiver causes a shift of the image away from the midline. In the study, the level differences, delta Ls, necessary to position sound images at 0 and +/- 12 degrees azimuths were measured. The baseline data were collected for 10 normally hearing subjects in unaided and aided conditions. In the aided conditions binaural aids were balanced (equal gains) or unbalanced (10 dB disparity in gains). The normally hearing subjects positioned the image on the midline with a group mean delta L of 0 dB in both unaided and balanced aided conditions. To position the image at +12 or -12 degrees azimuth they needed mean delta Ls that could be predicted from a theoretical equation. With unbalanced aids, a group mean delta L of +3 or -3 dB was needed for the midline image. The delta Ls for the side images also were shifted. For 12 hearing-impaired subjects with bilateral lossses, the midline delta Ls in unaided condition were within the normal range (+/- 2 dB). For two monaural hearing aid users with long experience, the midline delta Ls were greater than normal. The delta Ls for the side images were equal to or greatr than delta Ls for normally hearing subjects. In aided balanced and/or unbalanced conditions, some hearing-impaired subjects needed delta Ls for the midline image outside the normal range, and some could not position the image at the side azimuths. It was concluded that the binaural hearing aids can be a source of receiver asymmetry.

Professional and lay observers' impressions of preschoolers wearing hearing aids.

This study determined whether professional and lay observers had similar impressions of preschoolers wearing hearing aids and if the size of the aid affected ratings. Stimuli consisted of three photographic slides of nine normally-hearing and speaking male preschoolers wearing (1) a body-type hearing aid, (2) a post-auricular type aid, and (3) no aid. Slides were accompanied by taped speech samples. Stimuli were presented to 75 professional and 75 lay observers who rated the children on a semantic differential scale containing 15 adjectives. Ratings were submitted to a factor analysis revealing Factor I as achievement and Factor II as appearance. Results of MANOVAs revealed that neither professional nor lay observers discriminated against the children on appearance regardless of the presence of a hearing aid, but that both groups rated them significantly poorer on achievement when an aid was present. Lay observers' ratings showed a bias against the size of the aid, while professionals exhibited negative impressions whenever an aid was present, regardless of its size. These findings indicate that the "hearing aid effect" was present on variables of achievement even for normal-hearing preschoolers.

Multidimensional scaling of quality judgments of speech signals processed by hearing aids.

Perceptual dimensions underlying similarity ratings and preference judgments of the quality of hearing-aid-processed speech were derived via multidimensional-scaling procedures, and were correlated with 15 indices of electroacustic performance to determine those electroacoustic characteristics contributing maximally to quality judgements. Connected discourse was tape recorded through 20 conventional hearing aids and presented in a paired-comparison paradigm to ten normal listeners for similarity ratings and quality preference judgments. Analysis of the group similarity matrices revealed only one definitive perceptual dimension, low-cutoff frequency, that was common to the listeners. In a three-dimensional INDSCAL solution, this electroacoustic factor correlated--0.87 with dimension 1. Listeners strongly preferred hearing aids with relatively low low-cutoff frequencies; dimension 1 correlated--0.76 with their preferences. The quality judgments of some listeners were found via KYST analysis to exhibit a multidimensional structure, with low-cutoff frequency remaining the most salient dimension. Secondary dimensions varied across these several listeners, and included response irregularity, equivalent input noise level, high-cutoff frequency, and intermodulation distortion. Thus, the data provided evidence that, while low-cutoff frequency dominates listener judgments a multidimensional model may underlie the perceptual strategies used by some listeners to form quality judgments of hearing-aid-processed speech.

Hearing aid measurements using the revised standard: reducing variability and determining test system accuracy.

Unlike previous standards, the revised hearing aid standard, (ANSI S3.22-1976), specifies tolerance requirements for the electroacoustic characteristics of hearing aids. It is essential, therefore, that measurements of performance be made as accurately as possible. To assess the precision with which these measures can be made in a clinical environment, five hearing aids of the same model were each tested five times using Bruel and Kjaer instrumentation. When possible, data were recorded directly from the meter of the measuring amplifier as well as from the chart paper. The variability of the results was always less when data were obtained from the meter than from the chart. The ratio of the variability(meter:chart) differed depending on the test being made. The accuracy of the test system was derived (as required by the standard) both theoretically and empirically. When its estimated tolerances wee added to the tolerances permitted for the aids, all hearing aids were found to perform well within the limits of the standard except for one measurement on one aid.

The intelligibility of whitened and amplitude compressed speech in a multitalker background.

This experiment determined the effects of amplitude compression on speech intelligibility when both a target speech signal and a competing message were whitened and amplitude compressed. The target CNC discrimination words were electrically mixed with a competing message composed of five talkers. This composite signal was presented to normal hearing subjects in four ways: unmodified, whitened, whitened pplus 3:1 amplitude compression and whitened plus 10:1 amplitude compression. Discrimination functions were obtained for the CNC material by varying the signal-to-competition ratio. The unmodified and whitened speech yielded comparable discrimination functions, but reduced discrimination scores were obtained with the whitened lus compressed speech. However, the reduction in speech discrimination for the whitened plus compressed speech was slight and was most evident when the target signal and the competing background were at the same intensity.

Frequency response characteristics of FM mini-loop auditory trainers.

Personally sized inductance loops (mini-loops) now are available for use with an FM classroom amplification system and the student's personal ear-level hearing aid. Frequency response characteristics of five commercially-available hearing aids were assessed 1) using hearing aid test equipment available in most audiology clinics, with the hearing aid on microphone setting and 2) in a public school classroom, with the hearing aid on telecoil setting and operating with an FM mini-loop system. Clinic and classroom characteristics of the conventional FM receiver-insert earphone auditory trainers also were assessed. Results showed that the personal hearing aids' classroom performance could not be predicted from their clinic performance. Results also showed that gain provided by the environmental microphone circuit of the FM receiver-insert earphone units was uniformly higher than that provided by the teacher-microphone signal route.