Ruth A. Bentler

Optimal Outcome Measures, Research Priorities, and International Cooperation

&NA; The participants in the Eriksholm Workshop on “Measuring Outcomes in Audiological Rehabilitation Using Hearing Aids” debated three issues that are reported in this article. First, it was agreed that the characteristics of an optimal outcome measure vary as a function of the purpose of the measurement. Potential characteristics of outcome self‐report tools for four common goals of outcome measurement are briefly presented to illustrate this point. Second, 10 important research priorities in outcome measurement were identified and ranked. They are presented with brief discussion of the top five. Third, the concept of generating a brief universally applicable outcome measure was endorsed. This brief data set is intended to supplement existing outcome measures and to promote data combination and comparison across different social, cultural, and health‐care delivery systems. A set of seven core items is proposed for further study.

Transfer functions and correction factors used in hearing aid evaluation and research.

In hearing aid research and application it is often necessary to transform the sound pressure level or acoustic gain measured at one physical point (e.g., 2 cc coupler) to an equivalent value at another physical point (e.g., tympanic membrane). Results of currently available studies on various transformations are summarized in this report. When no data were available, the desired transfer function was calculated as a linear combination of known contributing transfer functions. Values are given for the center frequencies of 1/3 octaves and critical bands.

A review of past research on changes in hearing aid benefit over time.

&NA; Hearing aid benefit refers to a relative change in performance on a particular measure between aided and unaided listening conditions. A number of studies in recent years have investigated the hypothesis that hearing aid benefit increases over time after the initial fitting of the aid. Both objective (speech recognition) and subjective (questionnaire) measures have been used to measure hearing aid benefit. Some studies have reported a positive increase over time in group mean benefit, and some have reported no change in benefit, whereas none have reported a group mean negative change in benefit. However, individual subjects in these studies can show changes in benefit in either a positive or negative direction. The variability across subjects in each study has been large in comparison with the observed amount of benefit increase. In this review of the literature, it is argued that the studies present essentially similar results and the range of values across subjects in the various studies shows considerable overlap. Although there does appear to be a tendency for hearing aid benefit to increase over time, there are other, much stronger, factors influencing changes in hearing aid benefit that make it impossible at present to predict which patients will show a reliable increase (or decrease) in hearing aid benefit over time. (Ear & Hearing 1996;17;14S‐28S)

Digital noise reduction: Outcomes from laboratory and field studies

The purpose of this study was to determine the impact of a digital noise reduction (DNR) scheme implemented in a current commercial hearing aid. In a double-blinded design, three conditions of onset time (4, 8, 16 seconds) were randomly assigned to the 25 subjects, plus one condition wherein the noise-reduction feature was disengaged. Subsequently, a fifth trial/condition, wherein the subject had access to three memories in which the different onsets were programmed, was carried out. For each of the five conditions, the subjects had an at-home trial, prior to obtaining self-report measures. Laboratory measures of speech perception showed no effect of the DNR, with or without the provision of visual cues. Laboratory-based ratings of ease of listening showed DNR-on (all onset times) to be rated significantly better than DNR-off; for ratings of listening comfort, the 4-second onset time was rated significantly lower (poorer) than the 8-second onset or the DNR-off condition; for ratings of sound quality, DNR-on or -off had no differential effect. Self-report measures indicated significantly higher aversiveness in the DNR-off condition compared to the pre-test scores

Guidelines for choosing a self-report outcome measure.

&NA; A table of available self‐report inventories used throughout the world is provided with references for obtaining necessary psychometric data for research or clinical applications. Considerations for choosing an inventory (reliability, validity, and content appropriateness) are discussed and issues related to group versus single‐subject applications examined. It is preferable that translation and revalidation of existing outcome measures be considered above developing new ones for international application.

The effect of test signal type and bandwidth on the categorical scaling of loudness

Recently several methods for obtaining clinical measures of loudness growth through the use of categorical scaling (CS) have been proposed for the selection of hearing aids. These methods use differing test signals or suggest frequency-specific level corrections in an attempt to reflect the loudness perception of hearing aid-processed speech. While some decisions regarding the stimuli utilized for loudness perception procedures are based on measured relationships to speech signals, the effect on loudness perception of changing signal type and bandwidth (as measured by CS) remains unclear. The relationships between the CS loudness growth of signals of differing type, (pure tones, noise bands, filtered/temporally inverted/passband speech) and bandwidth were examined for subjects with both normal and impaired hearing. Results suggest that when the bandwidth is similar (e.g., pure tone and 1/3 oct), signal type does not have significant bearing on loudness perception. As expected, increasing the bandwidth beyond the critical band affected loudness growth, as wideband speech stimuli were judged to be significantly louder than narrow-band speech at equivalent overall sound levels. In this investigation, similar loudness growth patterns were noted across category ratings for all test signal bandwidths. In contrast, loudness growth data obtained using an intelligible speech signal [Cox et al., The American Academy of Audiology (1994a)], revealed loudness growth patterns for speech were fundamentally different than those obtained for tones. Implications for hearing aid fitting strategies are discussed.

Amplification With Digital Noise Reduction and the Perception of Annoying and Aversive Sounds

Hearing aid users report difficulties using their hearing aids in noisy environments. Problems include understanding speech, loudness discomfort, and annoyance with background noise. Digital noise reduction algorithms have been promoted as a method to solve speech understanding and comfort in noise problems. Research has failed to find improved speech understanding in noise. Little is known about how digital noise reduction affects noise annoyance and aversiveness. The goals of this investigation were to determine how a specific digital noise reduction system affects hearing aid users’ perception of noise annoyance and aversiveness and to compare their perceptions to those of normal-hearing listeners. Ratings of noise annoyance and of aversiveness were obtained from 49 participants with moderate sensorineural hearing loss before fitting and after 3 weeks of hearing aid use. Findings were compared to measures obtained from normal-hearing listeners. Perceived annoyance and aversiveness increased with amplification. Annoyance and aversiveness with the hearing aid approximated normal perception. The results of this investigation suggest the need for counseling patients about realistic expectations related to annoyance and aversiveness of sounds at the time of hearing aid fitting.

Impact of digital Labeling on outcome measures

Objective The purpose of this study was to determine whether the label attached to the hearing aid being presented would bias outcome measures towards newer technological designs. Design Two groups of subjects participated in this investigation. The groups were matched for age, gender, previous hearing aid experience, degree and configuration of hearing loss. Group A wore each of two digital hearing aids for 1 mo; Group B wore the same digital hearing aid for 2 mo, but the subjects were given the impression they were changing hearing aids after 1 mo. In each group the subjects were told that one of the months they were wearing a “digital” hearing aid and one of the months they were wearing a “conventional” hearing aid. Outcome measures consisted of a number of behavioral speech perception tasks and self-report measures, each completed at the onset and after 1 mo use with the hearing aids. Results Labeling effects were observed for many of the outcome measures. Using a mixed-model factorial analysis of variance to control for irrelevant variables and to explore interaction terms, prejudice (digital versus conventional labeling) was treated as a within-subject factor while the subject group (A or B) and clinician were treated as between-subject factors. Although only the APHAB RV and BN scales showed significant labeling effects on their own, the group of tests used in this study showed a significant labeling effect as a whole (p < 0.01). The total influence of labeling and related interaction terms indicated labeling-related effects accounted for 2 to 32% of the variance in individual outcome measures. Discussion The results of this investigation indicate a need for double-blinding in hearing aid research aimed at assessing the effectiveness of newer technologies, as well as a need for clinicians to critically evaluate the research describing the potential advantages of certain circuit options.

Comparison of hearing aids over the 20th century.

Objective To measure hearing aid performance using circuitry representative of the major eras of technological advancement during the 20th century. Design Twenty subjects with audiometric profiles consistent with hearing aid candidacy were fit with each of seven hearing aids. No directional microphones were used and binaural benefit was not assessed. Each hearing aid was fit to the strategy or fitting scheme of the era, or that which was intended by the presenting manufacturer. Electroacoustic and/or real ear measures of gain, output, bandwidth, and distortion were obtained. Objective outcome measures assessing speech perception in backgrounds of noise were obtained. Subjective outcome measures of sound quality and ease of listening were obtained in the laboratory and in real life settings. Results Electroacoustic and real ear measures indicate that gain and bandwidth have increased, and output and distortion have decreased with current electronic aids. Speech perception ability across the different outcome measures showed significantly poorer performance with the body and linear hearing aids when input levels were high; when input levels were low, outcome measures with hearing aids using a dynamic range compression were not negatively affected. At the most adverse signal to noise ratios, none of the hearing aids was shown to be superior. Measured bandwidth did not correlate highly with speech perception ability for any of the objective outcome measures used. For the subjective measures of sound quality done in a blinded manner, no significant differences were found across different listening situations for current hearing aids. Conclusions The two most important factors for aided speech perception appear to be the audibility and distortion of the signal. No current compression scheme proved superior with the outcome measures used in this investigation.

Does hearing aid benefit increase over time

In a recent tutorial for the journal, Palmer et al. [J. Acoust. Soc. Am. 103, 1705-1721 (1998)] reviewed the literature on the potential for increases in hearing aid benefit over time (acclimatization). Their review might leave some readers with the impression that acclimatization has implications for the fitting and selection of hearing aids today. We (Turner and Bentler), along with two other researchers in the field (Humes and Cox), conducted a similar review of the literature a few years earlier [Turner et al., Ear and Hearing 17, 14S-28S (1996)] and found little evidence of a robust effect. The bulk of the existing evidence, including the most recent studies on this topic, support earlier conclusions, i.e., that there is no evidence for the existence of a strong acclimatization effect in current hearing aid use.