Rauna K. Surr

Real-world performance of directional microphone hearing aids

Difficulty understanding speech in the presence of background noise is a common complaint of persons with impaired hearing. Currently, directional microphones are the only option available in hearing aids that offer the potential of significantly improving the signal-to-noise ratio (SNR) for the wearer. In this issue, Andrew Dittberner has provided options for measuring the directivity of the microphone system, while Todd Ricketts has presented laboratory evidence on the effectiveness of the various microphone designs. In this article, we will address the issue of real-world benefit. The directivity of directional microphone hearing aids is typically measured in an anechoic space. The purpose of making these physical measurements in a non-reverberant enclosure is to optimize the influence of the angle of incidence of the signal. In a more reverberant environment, direct and reflected sounds from a given source could enter both microphones at comparable intensities, thereby defeating the directional processing. Similarly, behavioral measures of directionality are typically made in a sound-treated test booth. The speech signal is presented through a loudspeaker positioned at 0o azimuth and the background noise is presented from one or more additional loudspeakers that are often positioned at azimuths corresponding to the primary nulls in the polar response of the directional microphones. Again, such a testing arrangement tends to optimize the directional processing. It goes without saying that persons with impaired hearing almost never encounter listening environments in daily living that are as sound-treated as an audiometric test booth, much less that are anechoic. Hence, it is not surprising that the performance of directional microphone hearing aids in everyday listening situations generally falls short of what might be expected based on measures of the directivity index or the directional advantage. The discrepancy between the performance of directional microphones in the test booth and that typically observed in everyday listening is illustrated by the results of Walden et al.1 We obtained test booth measures of speech recognition in background noise and everyday ratings of speech intelligibility in noisy listening situations for each microphone mode of a switchable omnidirectional/directional hearing aid. To obtain the test-booth measures, we used the Connected Speech Test (CST).2,3 Test sentences were presented from a loudspeaker positioned at 0o azimuth, and a multitalker babble was presented from loudspeakers positioned at 90o, 180o, and 270o. Two test conditions were included: a 60-

Performance of High Frequency Impaired Listeners with Conventional and Extended High Frequency Amplification

This study sought to determine if a high-pass hearing aid can provide increased improvement in word recognition and consonant discrimination over that of a conventional high frequency emphasis hearing aid in listeners with hearing loss limited to frequencies above 1 000 Hz. Word and consonant discrimination were assessed in quiet and in the presence of 12 talker speech babble for 10 subjects under three listening conditions: (1) unaided; (2) wearing a conventional high frequency emphasis hearing aid, and (3) wearing an experimental high-pass instrument. The speech testing materials included: (1) Northwestern University Auditory Test No. 6; (2) California Consonant Test, and (3) eight voiceless English consonants. Results suggested that both instruments provided similar benefit in quiet for improving word recognition and resolving consonant errors. For the noise condition, however, the experimental high-pass aid provided a considerable advantage in both word recognition and consonant identification and was particularly sensitive to reducing within- and between-manner voiceless consonant confusions. Furthermore, measurements of real-ear gain revealed that the high-pass aid afforded considerably greater acoustic gain above 4 000 Hz than that shown for the conventional high frequency emphasis hearing aid,20

Comparison of Linear and K-Amp circuits

Objective: To evaluate hearing aid user preference for Linear Class D or Class D with K‐Amp™ circuit. Design: Eighteen subjects, experienced with Class A hearing aid use, were given a choice of binaural hearing aids with either Linear Class D circuits or Class D with K‐Amp™ circuits after consecutive 30 day trial periods with each set of instruments. The patients also rated the benefit obtained from each circuit using the Profile of Hearing Aid Benefit (PHAB). Results: There was no significant difference in the number of subjects who chose one or the other of the circuits. Further, the PHAB scores showed no statistically significant differences between the two circuits. In most cases, the instruments rated highest on each of the subscales by an individual subject were also the ones preferred based on the 30 day trial. Conclusions: Hearing aids with either Class D Linear or Class D with K‐Amp™ circuits provided significant benefit in many everyday listening environments for individuals with a mild to moderate degree of hearing loss. Subjective choice between the Linear Class D and the K‐Amp™ circuits was relatively evenly divided.

Comparison of three hearing aid fittings using the speech intelligibility rating (SIR) test

This study compared the effects of three different hearing aids on subjective ratings of speech intelligibility. Insertion gain measurements on KEMAR indicated that the hearing aid fittings differed primarily in midfrequency gain. The test passages of the Speech Intelligibility Rating Test (SIR) were recorded onto tape through each hearing aid. The processed passages were presented monaurally to 13 subjects with hearing loss limited to frequencies above 2000 Hz. They rated five passages through each frequency responses (FR) in a randomized order. Each subject was retested within 2 or 3 days to assess test-retest reliability. Results indicated that the FR with the most midfrequency amplification did not differ significantly from the aid with the least amount of midfrequency gain. However, the FR with intermediate midfrequency gain received significantly lower ratings than did FR with most gain. Examination of the data from individual subjects indicated that the SIR results did not show differences among the FRs for the majority of subjects.

Response of hearing aid wearers to the absence of a user-operated volume control

32 The Hearing Journal User-operated volume control April 2001 • Vol. 54 • No. 4 A user-operated volume control (VC) is an option rather than a standard feature in many hearing aids dispensed today, particularly those with wide dynamic range compression (WDRC) circuits. Theoretically, wearers of WDRC instruments can rely on the automatic gain function for comfort in different listening environments rather than having to adjust the volume manually when the acoustic environment changes. However, for experienced hearing aid users who have become accustomed to a user-operated VC, its absence may be an important factor in their adjustment to new instruments. In a recent large market survey measuring customer satisfaction with digital hearing aids, Kochkin reported that 28% of users of single-microphone hearing aids with WDRC and without manual VCs indicated that they wanted controls.1 In addition, he reported that consumers who did not want a VC gave substantially higher satisfaction ratings to their hearing aids than did those who wanted a control—81% and 42% for the two groups, respectively. In the study reported here, we examined the following questions: Do experienced users of linear amplification want a user-operated VC when starting to use instruments with WDRC? Would they prefer more or less volume? What are the characteristics of those hearing aid users who want to lower the volume in comparison with those who wish to raise it? This report will present data obtained from experienced hearing aid users questioned about their perceived need for a user-operated VC while adjusting to new WDRC amplification. The respondents were participants in clinical trials of ReSound WDRC hearing aids.

Effects of multi-talker competing speech on the variability of the California Consonant Test.

The interference effects of multi-talker speech babble on the California Consonant Test scores were examined. Phoneme recognition was assessed in a sound field in quiet and under 4 message-to-competition ratio conditions for norrnal-hearing subjects and in three MCR conditions for listeners with bilateral high-frequency sensorineural hearing loss. The noise interference functions for both subject groups were characterized by a gradual decline in recognition performance as the signal-to-noise ratio decreased. The slope of the function for the 2 groups was parallel with the mean scores for the hearing-impaired subjects approximately 30% lower than those for the normal hearers. Test-retest reliability across conditions was examined via correlational analysis and by computing test-retest difference scores for individual subjects. These data are discussed in terms of sampling theory for full-list and half-list presentations and probabilities of measurement error for determining significance between 2 scores.