Hearing-aid outcome measured following one month of hearing aid use by the elderly.

This study reports the results of a large number of hearing-aid outcome measures obtained from 173 elderly hearing-aid wearers following one month of hearing-aid use. All participants in this study were fit binaurally with identical full-concha in-the-ear (ITE) hearing aids having linear Class-D amplifiers with output-limiting compression. Outcome measures included several measures of speech recognition, as well as several self-report measures of hearing-aid performance, benefit, satisfaction, and use. Comparison of mean data from this sample of hearing-aid wearers to other larger sets of data, obtained previously for several of these measures of hearing-aid outcome evaluated in isolation, indicated that the participants in this study were representative of the participants in other larger-scale studies. Subsequent principal-components factor analysis of the data from this study indicated that there were seven distinct dimensions of hearing-aid outcome. Attempts to document the effectiveness and efficacy of hearing aids for elderly persons with impaired hearing will be most complete when assessing performance along all seven dimensions of hearing-aid outcome. Clinically efficient procedures for doing so are discussed.

Factors affecting the recognition of reverberant speech by elderly listeners.

Elderly listeners have been shown to experience greater difficulty with speech understanding than young listeners. The greater difficulty with speech understanding in elderly listeners has been attributed, primarily, to their typical high-frequency sensorineural hearing impairment. However, not all of the observed difficulty can be accounted for by hearing thresholds, leaving the likelihood of additional suprathreshold processing deficits. This study investigates speech understanding in older people and the relative contributions of hearing threshold and age to speech understanding. Considering that temporal processing is thought to affect speech understanding, the study also assesses the contributions of hearing loss and age to modulation-preservation performance. Finally, individual differences in hearing loss, age, and modulation-preservation performance are examined to see if they are closely associated with individual differences in speech-recognition ability, especially among older listeners. The results of the study suggest that hearing loss is closely tied to both speech-recognition performance and to measures of modulation preservation. Although some of the analyses at first indicated an effect of age, it was shown that this could be attributed in part to slight elevations in hearing threshold. Finally, it was shown that individual differences in hearing loss and measures of modulation preservation and processing efficiency in noise are associated with speech-recognition performance and that, given these measures, speech recognition can be predicted quite accurately.

Prescribed clinician-fit versus as-worn coupler gain in a group of elderly hearing-aid wearers.

This study reports the prescribed, clinician-fit, coupler gain and the user-adjusted, as-worn coupler gain measured in 55 adults ranging in age from 60 to 83 years (M = 72.2 years). All participants were fit with linear, output-limiting compression, Class D circuits in full-concha, in-the-ear (ITE) shells. The NAL-R prescription rationale was used to generate target real-ear insertion gain (REIG) and coupler gain values. The clinician-fit gain was measured when the hearing aid was dispensed initially and was found to be a close match to the prescribed coupler gain. Both clinician-fit and as-worn gain were measured subsequently at approximately 2 weeks, 1 month, 6 months, and 1 year after the initial fitting. As-worn gain was measured as soon as the participant returned to the clinic for one of the follow-up visits by simply removing the hearing aids and placing them in the test chamber without any adjustments in volume control. At each follow-up session, the clinician then inspected the hearing aids, evaluated the instruments electroacoustically, readjusted the volume control to the setting used to match the prescribed gain in the initial fit, and measured the clinician-fit coupler gain once again. Results revealed that, despite the capability of the hearing aid to achieve coupler gain that is a close match to the prescribed gain, these users consistently selected as-worn gain that was generally 6-9 dB below that prescribed by the NAL-R formula. Of this 6-9 dB disparity, however, as much as 3-6 dB could be due to binaural summation effects not taken into consideration in the NAL-R prescriptive formula. In addition, 5.4% of the time, the hearing aids were found to be in less than ideal operating condition when removed for the as-worn gain measurements (e.g., weak or dead battery, cerumen occluding the sound bore, telecoil switch in the incorrect position).

A comparison of the aided performance and benefit provided by a linear and a two-channel wide dynamic range compression hearing aid.

The aided performance and benefit achieved with linear and two-channel wide dynamic range compression (WDRC) in-the-canal (ITC) hearing aids were established in 55 individuals. Study participants had been wearing either linear or adaptive-frequency-response (Bass Increase at Low Levels, BILL) ITC hearing aids for approximately one year before participation in this study. Outcome measures included aided performance and objective benefit in quiet and noise at a variety of speech levels (50, 60, and 75 dB SPL), at various levels of babble background (quiet, signal-to-babble ratios of +5 and +10 dB), and for various types of test materials (monosyllabic words and sentences in connected speech). Several subjective measures of aided performance (sound-quality judgments and magnitude estimates of listening effort) and relative benefit (improvement in listening effort and the Hearing Aid Performance Inventory, HAPI) were also obtained. Finally, self-report measures of hearing-aid use were also obtained using daily logs. Participants completed all outcome measures for the linear ITC hearing aids first, following 2 months of usage, and then repeated all outcome measures for the WDRC instruments after a subsequent 2-month period of use. In general, although both types of hearing aids demonstrated significant benefit, the results indicated that the WDRC instruments were superior to the linear devices for many of the outcome measures. This tended to be the case most frequently when low speech levels were used. Many of the performance differences between devices most likely can be ascribed to differences in gain, and prescriptive approaches (DSL[i/o] vs. NAL-R), for the fixed volume control testing performed in this study.

Dimensions of hearing aid outcome.

Dimensions of hearing aid outcome are explored in this paper. First, a variety of hearing aid outcome measures is defined including objective and subjective performance, objective and subjective benefit, satisfaction, and use. Following the definition of these terms, factor analysis is described as a statistical tool that can be of assistance in establishing the number and nature of the relevant dimensions of hearing aid outcome. Next, the results from three recent studies that included a variety of measures of hearing aid outcome are examined and factor analysis is applied to the data from each study. This examination leads to the conclusion that hearing aid outcome is a multidimensional construct, rather than unidimensional. The most complete description of hearing aid outcome will be obtained when including at least one measure of aided speech recognition performance, one or more measures of objective benefit in speech recognition, one or two subjective measures of sound quality or listening effort, and one measure of either subjective benefit, satisfaction, or use.

The relation between identification and discrimination of vowels in young and elderly listeners.

This study examined both the identification and discrimination of vowels by three listener groups: elderly hearing-impaired, elderly normal-hearing, and young normal-hearing. Each hearing-impaired listener had a longstanding symmetrical, sloping, mild-to-moderate sensorineural hearing loss. Two signal levels [70 and 95 dB sound-pressure level (SPL)] were selected to assess the effects of audibility on both tasks. The stimuli were four vowels, /I,e, epsilon, ae/, synthesized for a female talker. Difference limens (DLs) were estimated for both F1 and F2 formants using adaptive tracking. Discrimination DLs for F1 formants were the same across groups and levels. Discrimination DLs for F2 showed that the best formant resolution was for the young normal-hearing group, the poorest was for the elderly normal-hearing group, and resolution for the elderly hearing-impaired group fell in between the other two at both signal levels. Only the elderly hearing-impaired group had DLs that were significantly poorer than those of the young listeners at the lower, 70 dB, level. In the identification task at both levels, young normal-hearing listeners demonstrated near-perfect performance (M = 95%), while both elderly groups were similar to one another and demonstrated lower performance (M = 71%). The results were examined using correlational analysis of the performance of the hearing-impaired subjects relative to that of the normal-hearing groups. The results suggest that both age and hearing impairment contribute to decreased vowel perception performance in elderly hearing-impaired persons.

SCAN test-retest reliability for first- and third-grade children.

The SCAN is a popular screening test that was developed to provide a rapidly administered, standardized method for determining the potential of central auditory processing disorder (CAPD) in children between the ages of 3 and 11 years. It can be administered in 20 minutes with a portable stereo cassette player and contains three subtests: filtered words (FW), auditory figure ground (AFG), and competing words (CW). Published SCAN test-retest reliability data (Keith, 1986) used a 6-month retest interval and indicated that SCAN scores may be unreliable. No additional reliability data are available, and studies indicate that SCAN has been used by both researchers and clinicians despite reliability concerns. This investigation examined the stability of SCAN outcomes for 25 first-grade and 22 third-grade children (ages 6 to 9 years) using a 6- to 7-week retest interval. Time of day and examiner were held constant, and participants were normal-hearing, were Caucasian, and spoke English as their primary language. ANOVA outcomes indicated that both raw and standard scores improved significantly from Test 1 to Test 2 for two of the three SCAN subtests (FW and CW) and for the composite (COMP) score. Additionally, COMP-percentile-rank and age-equivalent outcomes demonstrated significant improvement from test to retest for both grades. The AFG subtest was the only SCAN measure for which a significant test-retest difference did not emerge. The highest test-retest correlation values (r) were moderately strong (0.70 < or = r < or = 0.78) and occurred for the CW and COMP scores. Implications of correlations and factor analyses are discussed. It is suggested that examiners base recommendations for additional testing, follow up, and remediation on the COMP score only. Further, it appears that second administration of the SCAN can provide a better estimate of an individual child's best performance, but lack of second-score norms confounds simple interpretation of such scores.

A comparison of the benefit provided by well-fit linear hearing aids and instruments with automatic reductions of low-frequency gain.

In this clinical study, 110 patients seen at three different clinical facilities were fit binaurally with linear, in-the-canal (ITC) hearing aids. All patients were new hearing aid users. Each of the hearing aids was equipped with an adjustable control that could be set by one of the audiologists (Audiologist A) at each site to convert it from a linear instrument to an experimental nonlinear one with automatic reduction of low-frquency gain at high input levels (or base increase at low levels, BILL). Both the patient and the audiologist performing the outcome testing at each site (Audiologist B) were blind as to the present setting of the hearing aid. Each participant was enrolled in the study for a total of 12 weeks, with the hearing aid set to either the linear or BILL-processing mode of operation for the first 8 weeks and the opposite setting for a subsequent 4-week period. In summary, this was a prospective, doubleblind, crossover study of 110 new hearing aid users. Outcome measures focused on hearing-aid benefit and included both objective and subjective measures. Objective measures were derived from scores on the Northwestern University Auditory Test NO. 6 (NU-6) and the Connected Speech Test (CST) obtained for all possible combinations of two speech presentation levels (60 and 75 dB SPL) two types of background noise (cafeteria noise and multitalker babble), and two signal-to-noise ratios (+5 and +10 dB). Subjective outcome measures included magnitude estimation of listening effort (MELE), the abbreviated form of the Hearing Aid Performance Inventory (HAPI), and estimations of hearing-aid usage based on daily-use logs kept by the participants. All of these measures were used to evaluate the benefit provided by linear amplification and the benefit resulting from the experimental BILL processing. Participant preferences for the experimental BILL-processing scheme or linear processing were also examined by using a paired-comparison task at the end of the study. Results were analyzed separately for three subgroups of patients (mild, moderate, severe) formed on the basis of their average hearing loss at 500, 1000, 2000, and 4000 Hz. In all three subgroups, significant improvement in performance was observed for linear amplification and for BILL processing when compared to unaided performance. There were no significant differences in aided performance, however, between linear processing and the experimental BILL processing.

Identification of multidimensional stimuli containing speech cues and the effects of training.

The purpose of this study was to determine how listeners with normal hearing make use of cues from multiple, independent stimulus dimensions when classifying synthesized stimuli containing acoustic cues found in speech. Listeners classified synthesized stimuli that differed on three independent and discriminable dimensions. The three dimensions of the stimuli included: (1) the fricative spectrum center frequency; (2) the slope of the frequency transition; and (3) the duration of the temporal gap. Each of the three dimensions could take on one of three possible values. Twenty-seven stimuli were synthesized using all possible combinations of the values on the three dimensions. Multidimensional scaling of paired-comparison similarity judgments confirmed the existence of three perceptual dimensions. Listeners were then trained to classify three exemplar stimuli as "circle," "triangle," and "square," respectively. Following this training, subjects classified all 27 stimuli as "circle," "triangle," and "square." From this it was determined how each listener's attention was distributed among the dimensions. Results indicated the listeners did not pay equal attention to the three stimulus dimensions. In addition, it was demonstrated that it was possible to train a listener to attend to a dimension that was not previously used to classify the stimuli.

Evaluation of the use of a new compact disc for auditory perceptual assessment in the elderly.

The present study examined the performance of 40 normal-hearing young adults and 38 elderly adults, some normal hearing and some hearing impaired, on the Department of Veterans Affairs' new compact disc (VA-CD) for auditory perceptual assessment. Principal-components factor analyses were performed on the test scores from each group of subjects with very similar results obtained from each group in terms of the number of factors identified (3), the percentage of variance explained by these factors individually and collectively (about 72%), and the association of various test scores with each factor. The 10 tests examined here were found to be associated with three underlying factors identified as a general speech-understanding ability (about 42% of variance), temporal sequencing capacity (about 18% of variance), and processing ability under conditions of dichotic competition (about 12% of variance). Among the elderly, hearing loss was strongly and negatively associated with general speech-recognition ability, whereas age was moderately associated with the other two factors. Test scores for several measures of auditory perceptual processing were negatively affected by the presence of peripheral hearing loss in the elderly even when administered at the highest recommended presentation level (90 dB SPL). In addition, some tests among those examined were found to have inadequate test-retest reliability for clinical use with the elderly.

Reliability and stability of various hearing-aid outcome measures in a group of elderly hearing-aid wearers.

Twenty elderly persons with hearing impairment were fit with binaural in-the-ear hearing aids and followed for a 6-month period post-fit. Several hearing-aid outcome measures were obtained at 0, 7, 15, 30, 60, 90, and 180 days post-fit. Outcome measures included (a) objective measures of benefit obtained with nonsense-syllable materials in quiet (CUNY Nonsense Syllable Test, NST) and sentences in multitalker babble (Hearing in Noise Test, HINT); (b) two subjective measures of benefit, one derived from pre-fit/post-fit comparisons on a general scale of hearing handicap (Hearing Handicap Inventory for the Elderly, HHIE) and the other based on a subjective scale of post-fit hearing-aid benefit (Hearing Aid Performance Inventory, HAPI); (c) a questionnaire on hearing-aid satisfaction; (d) an objective measure of hearing-aid use; and (e) a subjective measure of hearing-aid use. Reliability and stability of each measure were examined through repeated-measures analyses of variance, a series of test-retest correlations, and, where possible, scatterplots of the scores against their corresponding 95% critical differences. Many of the measures were found to be both reliable and stable indicators of hearing-aid outcome.

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

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.

Speech understanding in the elderly.

Three basic hypotheses regarding the speech-understanding difficulties of the elderly are reviewed: the peripheral, central-auditory, and cognitive hypotheses. Evidence obtained in our laboratory and in others is reviewed regarding the viability of each hypothesis. It is concluded that the strongest support exists for the peripheral hypothesis. Specifically, individual variations in the amount of sensorineural hearing loss among the elderly are most responsible for individual variations in speech-understanding performance. ("Speech understanding" is used throughout this article as a general term for the proportion of a speech signal that is accurately perceived by a listener whether in a discrimination, identification, recognition, or comprehension paradigm.) The focus to date, however, has been placed on monaural speech understanding measured in quiet, noise, or reverberation. It is possible that a more complex picture may yet emerge for other forms of temporally distorted speech or for dichotic measures of speech understanding.

Identification of multidimensional complex sounds having parallel dimension structure.

The present series of experiments examined the ability of normal-hearing listeners to make use of cues from multiple, independent stimulus dimensions when classifying multidimensional complex sounds. Ten listeners classified complex sound pulses that differed along three independent dimensions. The stimuli were 100 ms in duration and were synthesized using five simultaneous sinusoids. The three dimensions of the complex stimuli manipulated in this experiment were harmonicity, spectral shape, and amplitude envelope. Each stimulus dimension could take on one of two values, referred to here as target or nontarget. Eight stimuli were synthesized using all possible combinations of the dimension values. Subjects were trained to label two stimuli, the two having either all-target or all-nontarget values, as "+" and "0," respectively. Following this training, subjects were asked to classify all eight stimuli as either "+" or "0." Results of this experiment indicated that listeners preferred to classify these stimuli on the basis of one stimulus dimension. However, the preferred dimension was not the same for all of the listeners. In addition, it was demonstrated that it was possible to train an individual to use a dimension other than the one or two initially preferred when classifying the stimuli.

Factors associated with individual differences in clinical measures of speech recognition among the elderly.

In the present study, the speech-recognition performance of 50 subjects aged 63 to 83 years was measured for a wide range of materials (nonsense syllables, monosyllabic words, sentences) and listening conditions (presentation levels of 70 and 90 dB SPL, both in quiet and in a noise background). In addition to complete audiologic evaluations, measures of auditory processing (the Test of Basic Auditory Capabilities [TBAC], Watson, 1987) and cognitive function (Wechsler Adult Intelligence Scale-Revised [WAIS-R], and the Wechsler Memory Scale-Revised [WMS-R], Wechsler, 1981, 1987) were obtained from all subjects. Principal component analyses were applied to each of the three sets of measures (speech-recognition, auditory, and cognitive) prior to examining associations among the sets using canonical analyses. Two principal components captured most of the systematic variation in performance sampled by the set of 20 speech-recognition measures. Hearing loss emerged as the single largest factor associated with individual differences in speech-recognition performance among the elderly, accounting for 70-75% of the total variance in speech-recognition performance, with the measures of auditory processing and cognitive function accounting for little or no additional variance.

Two experiments on the temporal boundaries for the nonlinear additivity of masking.

The present paper describes the results from two experiments which explored the temporal boundary between overlapping and nonoverlapping maskers and its effects on the additivity of masking. In the first experiment, detection thresholds for a short-duration 1000-Hz signal were measured in the presence of two equal-duration broadband maskers which varied in degree of temporal overlap. Following complete overlap of maskers, the temporal separation of masker onsets was systematically varied to create conditions ranging from partially overlapping simultaneous masking to combined forward and backward masking. The signal was always temporally centered between the onset of the first masker and the offset of the second masker. Nonlinear additivity of masking occurred for the majority of subjects when maskers and signal did not overlap, whereas linear additivity resulted for all subjects when the maskers and signal overlapped. In the second experiment, two separate forward maskers were used so that masker/masker overlap could be manipulated independent from masker/signal overlap. Maskers were changed gradually from temporally overlapping, or concurrent, forward maskers to sequential forward maskers. Results for all subjects showed nonlinear additivity for all combined-masker conditions. Together, these two experiments indicated that nonlinear masking additivity is observed when the signal does not overlap temporally with the maskers. However, when maskers and signal overlap temporally (and spectrally), linear additivity is observed.

Effects of age on serial recall of natural and synthetic speech.

The present study addressed the effects of aging on auditory serial-recall performance for natural and synthetic words. Word difficulty, measured in terms of frequency of occurrence and phonological similarity, and rate of presentation were also manipulated in an effort to determine which processes underlying serial-recall performance, if any, were affected by aging. Results indicated that age per se had little effect on short-term (working) memory as measured by the serial recall of monosyllabic words. Rate of presentation had little effect on recall for either subject group. Word difficulty, on the other hand, affected recall for both groups, with easy words being more readily recalled than hard words.

Evaluating a speech-reception threshold model for hearing-impaired listeners.

Plomp's speech reception threshold (SRT) model [R. Plomp, J. Acoust. Soc. Am. 63, 533-549 (1978)] incorporates a distortion and an attenuation factor that are both expressed in dB and, for hearing-impaired listeners, are greater than 0 dB. The distortion factor is hypothesized to affect the SRT in quiet and in noise and suggests that a hearing-impaired listener will always demonstrate a higher SRT than a normal-hearing listener. The present study examines whether this distortion factor can be explained for many listeners simply by inaudibility of a portion of the speech spectrum. SRTs were obtained from normal-hearing and mild-to-moderately hearing-impaired listeners in quiet and at various noise levels. The results indicate that, at high noise levels, when the noise, rather than the quiet threshold, becomes the dominating factor, the SRT functions of both the normal and the mild-to-moderately hearing-impaired group converge and the distortion factor diminishes to zero. Predictions were also made using an articulation index and similar convergence of the two functions was observed.

Auditory filter shapes in normal-hearing, noise-masked normal, and elderly listeners.

To dissociate the effects of age and hearing impairment on changes in frequency selectivity, auditory filter shapes were measured at 2 kHz in four groups of subjects: (1) normal-hearing young subjects; (2) normal-hearing elderly subjects; (3) elderly hearing-impaired listeners; and (4) young normal-hearing listeners with simulated hearing losses. Filter shapes were derived using a modified version of the notched-noise procedure [Glasberg and Moore, Hear, Res. 47, 103-138 (1990)]. Equivalent rectangular bandwidths (ERBs) of auditory filters were not significantly different in young and elderly subjects with normal 2-kHz hearing. Furthermore, filter widths for young subjects with 20- and 40-dB simulated hearing losses overlapped with those obtained from elderly subjects with corresponding degrees of actual hearing loss. One measure that did show significant differences between actual and simulated hearing losses was the degree of filter asymmetry; auditory filters in hearing-impaired listeners were more asymmetrical than those obtained from noise-masked normal-hearing subjects. The dynamic range of auditory filters, however, was comparable for hearing-impaired and noise-masked listeners. Lastly, post-filter detection efficiency was also similar for young and elderly subjects with equivalent hearing levels. These findings suggest that the reduced frequency selectivity often reported for older listeners can be attributed, primarily, to hearing loss rather than increased age. Implications of the results for speech perception in the elderly and models of hearing impairment are discussed.