Mary T. Cord

Effects of amplification and speechreading on consonant recognition by persons with impaired hearing.

Objective This study sought to describe the consonant information provided by amplification and by speechreading, and the extent to which such information might be complementary when a hearing aid user can see the talker’s face. Design Participants were 25 adults with acquired sensorineural hearing losses who wore the GN ReSound BT2 Personal Hearing System binaurally. Consonant recognition was assessed under four test conditions, each presented at an input level of 50 dB SPL: unaided listening without speechreading (baseline), aided listening without speechreading, unaided listening with speechreading, and aided listening with speechreading. Confusion matrices were generated for each of the four conditions to determine overall percent correct for each of 14 consonants, and information transmitted for place of articulation, manner of articulation, and voicing features. Results Both amplification and speechreading provided a significant improvement in consonant recognition from the baseline condition. Speech-reading provided primarily place-of-articulation information, whereas amplification provided information about place and manner of articulation, as well as some voicing information. Conclusions Both amplification and speechreading provided place-of-articulation cues. The manner-of-articulation and voicing cues provided by amplification, therefore, were generally complementary to speechreading. It appears that the synergistic effect of combining the two sources of information can be optimized by amplification parameters that provide good audibility in the low-to-mid frequencies.

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-

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.

Assessment of auditory spatial awareness in complex listening environments.

In the real world, listeners often need to track multiple simultaneous sources in order to maintain awareness of the relevant sounds in their environments. Thus, there is reason to believe that simple single source sound localization tasks may not accurately capture the impact that a listening device such as a hearing aid might have on a listeners level of auditory awareness. In this experiment, 10 normal hearing listeners and 20 hearing impaired listeners were tested in a task that required them to identify and localize sound sources in three different listening tasks of increasing complexity: a single-source localization task, where listeners identified and localized a single sound source presented in isolation; an added source task, where listeners identified and localized a source that was added to an existing auditory scene, and a remove source task, where listeners identified and localized a source that was removed from an existing auditory scene. Hearing impaired listeners completed these tasks with and without the use of their previously fit hearing aids. As expected, the results show that performance decreased both with increasing task complexity and with the number of competing sound sources in the acoustic scene. The results also show that the added source task was as sensitive to differences in performance across listening conditions as the standard localization task, but that it correlated with a different pattern of subjective and objective performance measures across listeners. This result suggests that a measure of complex auditory situation awareness such as the one tested here may be a useful tool for evaluating differences in performance across different types of listening devices, such as hearing aids or hearing protection devices.

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.

Benefits of Nonlinear Frequency Compression in Adult Hearing Aid Users.

BACKGROUND Frequency-lowering (FL) algorithms are an alternative method of providing access to high-frequency speech cues. There is currently a lack of independent research addressing: (1) what functional, measureable benefits FL provides; (2) which, if any, FL algorithm provides the maximum benefit, (3) how to clinically program algorithms, and (4) how to verify algorithm settings. PURPOSE Two experiments were included in this study. The purpose of Experiment 1 was to (1) determine if a commercially available nonlinear frequency compression (NLFC) algorithm provides benefit as measured by improved speech recognition in noise when fit and verified using standard clinical procedures; and (2) evaluate the impact of acclimatization. The purpose of Experiment 2 was to (1) evaluate the benefit of using enhanced verification procedures to systematically determine the optimal application of a prototype NLFC algorithm, and (2) determine if the optimized prototype NLFC settings provide benefit as measured by improved speech recognition in quiet and in noise. RESEARCH DESIGN A single-blind, within-participant repeated measures design in which participants served as their own controls. STUDY SAMPLE Experiment 1 included 26 participants with a mean age of 68.3 yr and Experiment 2 included 37 participants with a mean age of 68.8 yr. Participants were recruited from the Audiology and Speech Pathology Center at Walter Reed National Military Medical Center in Bethesda, MD. INTERVENTION Participants in Experiment 1 wore bilateral commercially available hearing aids fit using standard clinical procedures and clinician expertise. Participants in Experiment 2 wore a single prototype hearing aid for which FL settings were systematically examined to determine the optimum application. In each experiment, FL-On versus FL-Off settings were examined in a variety of listening situations to determine benefit and possible implications. DATA COLLECTION AND ANALYSIS In Experiment 1, speech recognition measures using the QuickSIN and Modified Rhyme Test stimuli were obtained at initial bilateral fitting and 3-5 weeks later during a follow-up visit. In Experiment 2, Modified Rhyme Test, /sə/, /∫ə/ consonant discrimination task, and dual-task cognitive load speech recognition performance measures were conducted. Participants in Experiment 2 received four different systematic hearing aid programs during an initial visit and speech recognition data were collected over 2-3 follow-up sessions. RESULTS Some adults with hearing loss obtained small-to-moderate benefits from implementation of FL, while others maintained performance without detriment in both experiments. There was no significant difference among FL-On settings systematically obtained in Experiment 2. There was a modest but significant age effect in listeners of both experiments that indicated older listeners (>65 yr) might benefit more on average from FL than younger listeners. In addition, there were reliable improvements in the intelligibility of the phonemes /ŋ/ and /b/ for both groups, and /ð/ for older listeners from the FL in both experiments. CONCLUSIONS Although the optimum settings, application, and benefits of FL remain unclear at this time, there does not seem to be degradation in listener performance when FL is activated. The benefits of FL should be explored in older adult (>65 yr) listeners, as they tended to benefit more from FL applications.

Effects of high intensity on recognition of low‐ and high‐frequency speech in noise

For listeners with normal hearing (NH), speech recognition scores often decrease when intensities exceed moderate levels (rollover is observed). It is currently unclear whether the factors leading to rollover in NH listeners also limit performance for hearing‐impaired (HI) listeners at high sound levels. This study aimed at clarifying the stimulus conditions most clearly associated with rollover and whether rollover effects are similar for NH listeners and listeners with mild hearing impairment. In Stage 1, NH and HI listeners heard digitally‐filtered sentences and adaptive procedures were used to determine high‐ and low‐frequency bandwidths yielding 70%‐correct word recognition in quiet at moderate levels. In Stage 2, broadband and band‐limited stimuli (based on the high‐, and low‐frequency passbands measured in quiet in Stage 1) were tested at moderate levels in background noise. Noise levels were varied adaptively to determine signal‐to‐noise levels supporting 30%‐correct recognition. Stimulus conditio...

Unique challenges for hearing protection in military noise environments.

Military noise environments, and, in particular, the noise environments faced by dismounted soldiers on the battlefield, are characterized by wide variations in ambient level. Situations can quickly and unexpectedly change from quiet conditions where the sound of a snapping twig might alert the listener to hostile enemy activity to extreme noise conditions where firefights, explosions, or loud machinery create levels of noise that can cause hearing loss in a matter of minutes or seconds. This poses a unique challenge for the designers of military hearing protection, who must produce systems that provide enough comfort and acoustic transparency to convince users to consistently wear them in quiet conditions to ensure that they will be in place if an unexpected blast or other potentially damaging noise exposure occurs. In this talk, we discuss some of the issues that can influence the willingness of listeners to wear hearing protection for extended periods in quiet environments, including acoustic factors t...