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.

Understanding excessive SNR loss in hearing-impaired listeners.

BACKGROUND: Traditional audiometric measures, such as pure-tone thresholds or unaided word-recognition in quiet, appear to be of marginal use in predicting speech understanding by hearing-impaired (HI) individuals in background noise with or without amplification. Suprathreshold measures of auditory function (tolerance of noise, temporal and frequency resolution) appear to contribute more to success with amplification and may describe more effectively the distortion component of hearing. However, these measures are not typically measured clinically. When combined with measures of audibility, suprathreshold measures of auditory distortion may provide a much more complete understanding of speech deficits in noise by HI individuals. PURPOSE: The primary goal of this study was to investigate the relationship among measures of speech recognition in noise, frequency selectivity, temporal acuity, modulation masking release, and informational masking in adult and elderly patients with sensorineural hearing loss to determine whether peripheral distortion for suprathreshold sounds contributes to the varied outcomes experienced by patients with sensorineural hearing loss listening to speech in noise. RESEARCH DESIGN: A correlational study. STUDY SAMPLE: Twenty-seven patients with sensorineural hearing loss and four adults with normal hearing were enrolled in the study. DATA COLLECTION AND ANALYSIS: The data were collected in a sound attenuated test booth. For speech testing, subjects' verbal responses were scored by the experimenter and entered into a custom computer program. For frequency selectivity and temporal acuity measures, subject responses were recorded via a touch screen. Simple correlation, step-wise multiple linear regression analyses and a repeated analysis of variance were performed. RESULTS: Results showed that the signal-to-noise ratio (SNR) loss could only be partially predicted by a listener's thresholds or audibility measures such as the Speech Intelligibility Index (SII). Correlations between SII and SNR loss were higher using the Hearing-in-Noise Test (HINT) than the Quick Speech-in-Noise test (QSIN) with the SII accounting for 71% of the variance in SNR loss for the HINT but only 49% for the QSIN. However, listener age and the addition of suprathreshold measures improved the prediction of SNR loss using the QSIN, accounting for nearly 71% of the variance. CONCLUSIONS: Two standard clinical speech-in-noise tests, QSIN and HINT, were used in this study to obtain a measure of SNR loss. When administered clinically, the QSIN appears to be less redundant with hearing thresholds than the HINT and is a better indicator of a patient's suprathreshold deficit and its impact on understanding speech in noise. Additional factors related to aging, spectral resolution, and, to a lesser extent, temporal resolution improved the ability to predict SNR loss measured with the QSIN. For the HINT, a listener's audibility and age were the only two significant factors. For both QSIN and HINT, roughly 25-30% of the variance in individual differences in SNR loss (i.e., the dB difference in SNR between an individual HI listener and a control group of NH listeners at a specified performance level, usually 50% word or sentence recognition) remained unexplained, suggesting the need for additional measures of suprathreshold acuity (e.g., sensitivity to temporal fine structure) or cognitive function (e.g., memory and attention) to further improve the ability to understand individual variability in SNR loss.

Performance on tests of central auditory processing by individuals exposed to high-intensity blasts.

Thirty-six blast-exposed patients and twenty-nine non-blast-exposed control subjects were tested on a battery of behavioral and electrophysiological tests that have been shown to be sensitive to central auditory processing deficits. Abnormal performance among the blast-exposed patients was assessed with reference to normative values established as the mean performance on each test by the control subjects plus or minus two standard deviations. Blast-exposed patients performed abnormally at rates significantly above that which would occur by chance on three of the behavioral tests of central auditory processing: the Gaps-In-Noise, Masking Level Difference, and Staggered Spondaic Words tests. The proportion of blast-exposed patients performing abnormally on a speech-in-noise test (Quick Speech-In-Noise) was also significantly above that expected by chance. These results suggest that, for some patients, blast exposure may lead to difficulties with hearing in complex auditory environments, even when peripheral hearing sensitivity is near normal limits.

Implications of blast exposure for central auditory function: a review.

Auditory system functions, from peripheral sensitivity to central processing capacities, are all at risk from a blast event. Accurate encoding of auditory patterns in time, frequency, and space are required for a clear understanding of speech and accurate localization of sound sources in environments with background noise, multiple sound sources, and/or reverberation. Further work is needed to refine the battery of clinical tests sensitive to the sorts of central auditory dysfunction observed in individuals with blast exposure. Treatment options include low-gain hearing aids, remote-microphone technology, and auditory-training regimens, but clinical evidence does not yet exist for recommending one or more of these options. As this population ages, the natural aging process and other potential brain injuries (such as stroke and blunt trauma) may combine with blast-related brain changes to produce a population for which the current clinical diagnostic and treatment tools may prove inadequate. It is important to maintain an updated understanding of the scope of the issues present in this population and to continue to identify those solutions that can provide measurable improvements in the lives of Veterans who have been exposed to high-intensity blasts during the course of their military service.

A naturalistic approach to assessing hearing aid candidacy and motivating hearing aid use.

BACKGROUND: Although the benefits of amplification for persons with impaired hearing are well established, many potential candidates do not obtain and use hearing aids. In some cases, this is because the individual is not convinced that amplification will be of sufficient benefit in those everyday listening situations where he or she is experiencing difficulties. PURPOSE: To describe the development of a naturalistic approach to assessing hearing aid candidacy and motivating hearing aid use based on patient preferences for unamplified and amplified sound samples typical of those encountered in everyday living and to assess the validity of these preference ratings to predict hearing aid candidacy. RESEARCH DESIGN: Prospective experimental study comparing preference ratings for unamplified and amplified sound samples of patients with a clinical recommendation for hearing aid use and patients for whom amplification was not prescribed. STUDY SAMPLE: Forty-eight adults self-referred to the Army Audiology and Speech Center for a hearing evaluation. DATA COLLECTION AND ANALYSIS: Unamplified and amplified sound samples were presented to potential hearing aid candidates using a three-alternative forced-choice paradigm. Participants were free to switch at will among the three processing options (no gain, mild gain, moderate gain) until the preferred option was determined. Following this task, each participant was seen for a diagnostic hearing evaluation by one of eight staff audiologists with no knowledge of the preference data. Patient preferences for the three processing options were used to predict the attending audiologists' recommendations for amplification based on traditional audiometric measures. RESULTS: Hearing aid candidacy was predicted with moderate accuracy from the patients' preferences for amplified sounds typical of those encountered in everyday living, although the predictive validity of the various sound samples varied widely. CONCLUSIONS: Preferences for amplified sounds were generally predictive of hearing aid candidacy. However, the predictive validity of the preference ratings was not sufficient to replace traditional clinical determinations of hearing aid candidacy in individual patients. Because the sound samples are common to patients' everyday listening experiences, they provide a quick and intuitive method of demonstrating the potential benefit of amplification to patients who might otherwise not accept a prescription for hearing aids.

Clinical benefits and risks of bilateral amplification.

Clinicians are in the unique position of continually developing a foundation of evidence-based practice each time they evaluate a patient. This is true not only in the field of audiology, but also in all healthcare professions. Typically, evidence-based practice (EBP) is assimilated from a combination of a systematic review of current practices, practitioner experience, academic training and ongoing continuing education through review of journals, textbooks and attendance at meetings as well as informal discussions with colleagues. Clinicians are inundated with information from these sources, and they need to extract the necessary information and apply it to their specific patient population. Evidence-based practice as it applies to the non-medical treatment of hearing loss (with hearing aids) will be discussed. In addition, several studies based on clinical observations are presented for discussion.

Unilateral versus bilateral amplification for adults with impaired hearing.

This study compared unilateral and bilateral aided speech recognition in background noise in 28 patients being fitted with amplification. Aided QuickSIN (Quick Speech-in-Noise test) scores were obtained for bilateral amplification and for unilateral amplification in each ear. In addition, right-ear directed and left-ear directed recall on the Dichotic Digits Test (DDT) was obtained from each participant. Results revealed that the vast majority of patients obtained better speech recognition in background noise on the QuickSIN from unilateral amplification than from bilateral amplification. There was a greater tendency for bilateral amplification to have a deleterious effect among older patients. Most frequently, better aided QuickSIN performance was obtained in the right ear of participants, despite similar hearing thresholds in both ears. Finally, patients tended to perform better on the DDT in the ear that provided less SNR loss on the QuickSIN. Results suggest that bilateral amplification may not always be beneficial in every daily listening environment when background noise is present, and it may be advisable for patients wearing bilateral amplification to remove one hearing aid when difficulty is encountered understanding speech in background noise.

Predicting success with hearing aids in everyday living.

Persons with impaired hearing who are candidates for amplification are not all equally successful with hearing aids in daily living. Having the ability to predict success with amplification in everyday life from measures that can be obtained during an initial evaluation of the patient's candidacy would result in greater patient satisfaction with hearing aids and more efficient use of clinical resources. This study investigated the relationship between various demographic and audiometric measures, and two measures of hearing aid success in 50 hearing aid wearers. Audiometric predictors included measures of audibility and suprathreshold distortion. The unaided and aided signal-to-noise ratio (SNR) loss on the QuickSIN test provided the best predictors of hearing aid success in daily living. However, much of this predictive relationship appeared attributable to the patient's age.

Performance of custom-fit versus fixed-format hearing aids for precipitously sloping high-frequency hearing loss.

This study compared the real-ear response provided by custom-fit hearing aids to the closest matching fixed-format disposable hearing aids in patients with precipitous high-frequency hearing loss. Laboratory and field measures of aided performance were obtained to compare patient performance with the custom-fit and fixed-format hearing aids. In addition, coupler versus real-ear response differences were compared for the two hearing aid types. The results revealed that relatively close approximations to the real-ear aided responses of the custom-fit instruments were possible for most participants using seven fixed acoustic formats. No significant differences in mean performance between the two instrument types were observed for aided speech recognition or field ratings of aided performance, although mean patient satisfaction was lower for the disposable hearing aids. The real-ear to coupler difference was greater for the disposable hearing aid than for the custom-fit instruments, presumably owing to its deeper insertion into the ear canal.