Gender-specific effects of drugs on hearing levels of older persons.

As part of a study of human presbyacusis, a questionnaire on medicinal drug usage was given to 357 subjects (184 females, 173 males). Previous results from 211 subjects showed gender effects, that is, for males, none of the drugs had any measurable effects on hearing, whereas women taking calcium channel blockers (CCBs) had hearing levels 12 dB better than women not taking them; women taking beta adrenergic medication had hearing levels 20 dB poorer, and women taking antihistamine/cold preparations had hearing levels 9 dB poorer. Results from the original 211 subjects were confirmed when the sample size was increased from 211 to 357 subjects only for the beta adrenergic medications. Results for antihistamine/cold preparation medications showed small effects only for female subjects. Data from 13 additional female subjects who used CCBs showed hearing levels 10-14 dB poorer than predicted from the original data. Male data were consistent in both samples. The inconsistency for females could reflect sampling error. A more likely possibility is that since the original 10 subjects using CCBs had a mean age of 72 yr and the second sample of 13 had a mean age of 79.5 yr, poorer hearing levels might be anticipated because of the difference in chronological age and possibly duration of drug usage.

Auditory brainstem responses in younger and older adults for broadband noises separated by a silent gap.

Wave V of the auditory brainstem response was measured to two 50-ms broadband noise bursts separated by silent gaps of varied duration (4, 8, 32, or 64 ms) for younger and older adults with normal hearing. All subjects had measurable wave V responses to the first noise burst. However, for the second noise burst, three of eight older adults did not have responses with gap durations of 4 and 8 ms, and one of eight younger adults did not have a measurable response with a gap duration of 4 ms. When responses were present for older adults, latencies were similar to those of younger subjects but amplitudes were smaller. These results suggest age-related deficits in gap detection at the level of the brainstem in a group of aged subjects with no threshold elevation. Results are similar to those of Boettcher et al. (1996) using an identical paradigm in young and aged Mongolian gerbils.

The amplitude-modulation following response in young and aged human subjects.

The amplitude-modulation following response (AMFR) is a steady-state auditory response which may be an objective measure of intensity discrimination. Aged subjects with normal hearing have poorer intensity discrimination for low-frequency tones measured behaviorally, which would predict poorer AMFRs for low-frequency carriers. Experiment 1 was designed to assess age-related differences in AMFR characteristics. Response amplitudes were not significantly different among the young and aged groups for either carrier frequency (520 or 4000 Hz) or modulation depth (0--100%). Response phase did not vary systematically among groups. These results suggest that the AMFR may not be directly comparable to behavioral measures of intensity discrimination in aged subjects with normal hearing. To assess the contribution of high-frequency hearing loss on the AMFR in aged subjects, Experiment 2 compared AMFR amplitudes in aged subjects and in young subjects under the condition of high-pass masking. The amplitude of the AMFR was reduced at 520 Hz for both aged subjects and masked young subjects compared to unmasked young subjects, suggesting that reduced amplitudes in aged subjects with high-frequency hearing loss were associated with threshold elevations. Furthermore, the results suggest that the base of the cochlea contributes to the AMFR for low carrier frequencies.

Masking of auditory brainstem responses in young and aged gerbils.

Auditory brainstem responses (ABR) were recorded in the presence of low-pass (1 kHz cutoff) or high-pass (8 kHz cutoff) filtered noise in young (4-8 month) and aged (36 month) gerbils. For low-pass maskers, aged gerbils had higher masked thresholds at 2 and 4 kHz than young subjects. This was true for all aged subjects, including those with quiet thresholds similar to those of young controls. For high-pass masking, the majority of aged subjects had higher masked thresholds at 2 and 4 kHz than young controls; however, aged subjects with relatively normal quiet thresholds had masked thresholds similar to those of young subjects. A modified power-law (MPL) model was used to predict masked thresholds for aged subjects. Thresholds measured in the presence of low-pass noise were higher than predicted in many of the aged subjects, particularly those with near-normal quiet thresholds. In contrast, thresholds measured in the presence of the high-pass masker were similar to the predicted thresholds. These results suggest that: (a) excess masking occurred in aged subjects for low-pass, but not high-pass, maskers; (b) the excess masking occurred independently of quiet thresholds; and (c) excess upward spread of masking was related to the spectrum of the masker and not the 2 and 4 kHz regions of the auditory periphery.

Gender-specific effects of medicinal drugs on hearing levels of older persons.

As part of a large-scale study of presbyacusis, responses to a medicinal drug questionnaire from 85 female and 126 male human subjects were analyzed. Medicinal drugs were divided into 35 categories based on their pharmacologic effects. Subjects' ages ranged from 60 to 82 years. At least 10% of subjects reported taking drugs in 14 of 35 categories. Results were significantly different between female and male subjects. In men, none of the 14 categories showed a statistically significant relation to the pure-tone average (PTA) of 500, 1000, 2000, and 4000 Hz. In women, 3 of the 14 categories showed a statistically significant relation to the PTA. First, the average PTA of female subjects taking beta-adrenergic medication was 20 dB higher (poorer) than those not taking beta-adrenergic medication. Second, women taking antihistamine/cold preparations had an average PTA 9 dB higher (poorer) than those not taking antihistamine/cold preparations. Third, the average PTA of women taking calcium-channel blockers (CCBs) was 12 dB lower (better) than those not taking CCBs. In men, however, these drugs produced effects on the PTA of less than 3 dB. Differences between women and men were not explainable by differences in age or hearing level.

Auditory brain stem evoked response characteristics in developing infants.

The auditory brain stem response (ABR) of a single group of developing normal infants was examined longitudinally, from newborn through 6 months of age. A sufficiently broad range of stimulus variables was included to ensure that the auditory system was adequately sampled in order to demonstrate developmental principles. Findings indicate that there are no differences in wave V latency-intensity functions between infants and adults. For waves I, III, and V, absolute and interwave latency-repetition rate functions differ between infants and adults and undergo systematic changes throughout the first 6 months of life. The most dramatic ABR changes (between any two sequential test sessions in infants) occurred between the ages of newborn and 2 weeks, with less pronounced ABR changes beyond 2 weeks of age. The pattern of latency change for wave I was different from that for waves III and V. After 2 weeks of age, wave I latency was the same as the adult value at all repetition rates. In contrast, waves III and V were characterized by decreasing latency throughout the follow-up period. A curvilinear developmental model provided a satisfactory fit to ABR latency data.

Auditory brain stem evoked response characteristics in the full-term newborn infant.

The auditory brain stem response to click stimuli was investigated in a group of 50 full-term healthy newborns, as well as in a group of 20 older children and adults. The stimulus parameters of click level and click repetition rate were varied systematically to quantify the characteristics of the auditory brain stem response in the full-term newborn infant. The results reveal increased latencies for waves I, III, and V for all conditions among the newborns, relative to the older age group. The results suggest that the neurological system is the primary source of differences between newborns and older subjects, but do not rule out the possibility that external ear, middle ear, or cochlear mechanisms may also contribute to the differences observed.

Comments on the acoustic-reflex response for bone-conducted signals.

Previous studies which have measured acoustic-reflex responses to bone-conducted signals have not effectively differentiated reflex responses from artifacts. A convenient method for identifying such artifacts was developed and employed on some acoustic-reflex measures for bone-conducted signals. The findings indicated that artifacts result when a frequently-used acoustic admittance meter (Grason-Stadler 1720B) and a conventional bone vibrator were used to measure reflex responses for tonal and noise-activating signals. It was suggested that the method be employed in future studies which investigate the acoustic reflex in response to bone-conducted signals.

Age-related and gender-related changes in monaural speech recognition.

Previous studies of older listeners suggest age-related declines in speech recognition. However, the interpretation of these results is not straightforward because auditory thresholds, which account for the largest proportion of the variance in speech-recognition scores, also vary considerably with age. Here, effects of age, gender, and auditory thresholds on several measures of speech recognition were assessed for a large sample of individuals enrolled in a longitudinal study of age-related hearing loss. Participants ranged in age from 55-84 years. They were evaluated with a battery of conventional audiometric measures and speech-recognition materials, including NU-6 monosyllabic words, Synthetic Sentence Identification sentences, and high-context and low-context sentences from the Speech Perception in Noise test. Two analyses were conducted to assure that changes in speech-recognition scores with age were examined independently of age-related changes in auditory thresholds. In the first analysis, no significant differences in speech recognition were observed for individuals in three age groups (55-64, 65-74, 75-84 years) who were selected so that average puretone thresholds for the groups were within 5 dB. In the second analysis, using partial correlations to adjust both score and age for their association with average thresholds, significant declines with age were observed for males in maximum word recognition, maximum synthetic sentence identification, and keyword recognition in high-context sentences. For females, no significant changes in speech recognition with age were observed for any test.

Extended high-frequency thresholds in older adults.

Most measures of auditory sensitivity at extended high frequencies (frequencies greater than 8 kHz) have been obtained from listeners with normal hearing less than 40 years of age. The purpose of this study was (a) to measure thresholds at frequencies above 8 kHz in older listeners who, as a group, have elevated thresholds at lower frequencies, and (b) to assess test-retest reliability, age and gender effects, and the influence of thresholds below 8 kHz. Extended high-frequency (EHF) thresholds were measured for 162 older listeners (60-79 years) using a commercially available high-frequency audiometer, with a frequency range of 8 to 18 kHz and an intensity range of 0 to 110 dB SPL. Thresholds were measured once at the beginning of a 1- to 2-hour test session and then remeasured at the end of the test session. EHF thresholds of older listeners with normal hearing at conventional audiometric frequencies were substantially higher than the thresholds reported for younger listeners, with normal hearing by Dreschler and van der Hulst (1987). EHF thresholds of older listeners with hearing loss at conventional audiometric frequencies were further elevated as compared to older listeners with normal hearing. Differences in EHF thresholds between females and males were either not present or were reduced when gender differences in conventional audiometric thresholds were taken into account. No significant differences were seen in thresholds at 8 kHz and higher between the 60- to 69-and 70- to 79-year-old age groups. Results also indicated that thresholds above 8 kHz can be measured in older listeners within a clinically acceptable +/- 10 dB test-retest range.

Auditory filter characteristics and consonant recognition for hearing-impaired listeners.

To examine the association between frequency resolution and speech recognition, auditory filter parameters and stop-consonant recognition were determined for 9 normal-hearing and 24 hearing-impaired subjects. In an earlier investigation, the relationship between stop-consonant recognition and the articulation index (AI) had been established on normal-hearing listeners. Based on AI predictions, speech-presentation levels for each subject in this experiment were selected to obtain a wide range of recognition scores. This strategy provides a method of interpreting speech-recognition performance among listeners who vary in magnitude and configuration of hearing loss by assuming that conditions which yield equal audible spectra will result in equivalent performance. It was reasoned that an association between frequency resolution and consonant recognition may be more appropriately estimated if hearing-impaired listeners' performance was measured under conditions that assured equivalent audibility of the speech stimuli. Derived auditory filter parameters indicated that filter widths and dynamic ranges were strongly associated with threshold. Stop-consonant recognition scores for most hearing-impaired listeners were not significantly poorer than predicted by the AI model. Furthermore, differences between observed recognition scores and those predicted by the AI were not associated with auditory filter characteristics, suggesting that frequency resolution and speech recognition may appear to be associated primarily because both are degraded by threshold elevation.

Suggestions for optimizing reliability with the synthetic sentence identification test.

The reliability of the Synthetic Sentence Identification (SSI) test was determined for a group of 33 listeners with mild-to-moderate sensorineural hearing loss. Randomizations of the 10-item test were administered 12 times (six trials on each of two days) under identical listening conditions. Lists were presented monaurally, under earphones, at 90 dB SPL with a cafeteria background noise set at a signal-to-noise ratio (S/N) estimated (by adaptive procedure for each subject) to obtain 50% performance. Average scores ranged from 48.8% for Trial 1 to 67.9% for Trial 9. Reliability of the 12 measurements was determined by Pearson correlation, analyses of variance, and by testing individual differences in scores against a theoretical statistical distribution. Results evidenced large intra-subject variability, especially for the initial trials conducted in each testing session. However, if sufficient practice trials are presented each day under relatively difficult listening conditions, the scores on subsequent lists tend to remain relatively stable. Suggested procedures to optimize reliability are included.

Psychophysical suppression effects for tonal and speech signals.

This experiment assessed the benefits of suppression and the impact of reduced or absent suppression on speech recognition in noise. Psychophysical suppression was measured in forward masking using tonal maskers and suppressors and band limited noise maskers and suppressors. Subjects were 10 younger and 10 older adults with normal hearing, and 10 older adults with cochlear hearing loss. For younger subjects with normal hearing, suppression measured with noise maskers increased with masker level and was larger at 2.0 kHz than at 0.8 kHz. Less suppression was observed for older than younger subjects with normal hearing. There was little evidence of suppression for older subjects with cochlear hearing loss. Suppression measured with noise maskers and suppressors was larger in magnitude and more prevalent than suppression measured with tonal maskers and suppressors. The benefit of suppression to speech recognition in noise was assessed by obtaining scores for filtered consonant-vowel syllables as a function of the bandwidth of a forward masker. Speech-recognition scores in forward maskers should be higher than those in simultaneous maskers given that forward maskers are less effective than simultaneous maskers. If suppression also mitigated the effects of the forward masker and resulted in an improved signal-to-noise ratio, scores should decrease less in forward masking as forward-masker bandwidth increased, and differences between scores in forward and simultaneous maskers should increase, as was observed for younger subjects with normal hearing. Less or no benefit of suppression to speech recognition in noise was observed for older subjects with normal hearing or hearing loss. In general, as suppression measured with tonal signals increased, the combined benefit of forward masking and suppression to speech recognition in noise also increased.

Frequency selectivity for hearing-impaired and broadband-noise-masked normal listeners.

When evaluating frequency selectivity, it is difficult to determine if the deviation from normal performance observed for hearing-impaired listeners reflects abnormal cochlear function or normal, level-dependent changes in frequency selectivity. This experiment was designed to investigate the dependence of frequency-selectivity measures on threshold and signal level. Auditory-filter characteristics, critical ratios, forward-masked psychophysical tuning curves, and narrowband-noise masking patterns were obtained from normal-hearing listeners in quite and in the presence of broadband noise at five levels. These findings were then compared to previously obtained frequency-selectivity measurements for subjects with mild-to-moderate sensorineural hearing loss whose absolute thresholds are comparable to the normal-hearing listeners' masked thresholds. The results suggest that frequency selectivity deterioriates as threshold increases for all subjects. However, the poor frequency selectivity exhibited by hearing-impaired listeners may not be explained entirely by the effects of threshold and signal level. Nevertheless, because frequency selectivity is poorer in the normal auditory system at higher stimulus levels, the deviation from normal performance observed for hearing-impaired listeners may not be as large as previously suggested.

Associations among frequency and temporal resolution and consonant recognition for hearing-impaired listeners.

To examine the association between frequency and temporal resolution and speech recognition, auditory filter parameters, rates of masking decay, and stop-consonant recognition were determined for 9 normal-hearing and 24 hearing-impaired subjects. Speech-presentation levels were selected for each subject based on articulation index (AI) predictions. Results suggest that auditory filter widths and dynamic ranges were strongly correlated with pure-tone threshold, while time constants were not. Stop-consonant recognition scores for most hearing-impaired listeners were not significantly poorer than predicted by the AI model. Furthermore, differences between observed recognition scores and those predicted by the AI were poorly correlated with derived psychophysical parameter values, suggesting that measures of frequency and temporal resolution and speech recognition may appear to be associated primarily because of their dependence on auditory threshold.

Growth of low-pass masking of pure tones and speech for hearing-impaired and normal-hearing listeners.

Tonal thresholds and consonant recognition were measured in low-pass maskers as a function of masker bandwidth and spectrum level. Thresholds and consonant-recognition scores were obtained for normal-hearing subjects, and for pairs of normal-hearing subjects (who listened in threshold-equating background noise) and hearing-impaired subjects. Consonant-recognition scores were compared to scores predicted by a modified articulation index. Mean thresholds measured in low-pass maskers were higher for hearing-impaired than for normal-hearing subjects for signal frequencies above the masker. Slopes of functions relating thresholds for signals above the masker to masker spectrum level were not significantly different between hearing-impaired and normal-hearing subjects listening in spectrally shaped broadband noise (SSBB), but were shallower than slopes of masking functions for normal-hearing subjects listening without SSBB. Slopes of masking functions for signals within the masker were equivalent for all subjects. Slopes of functions relating consonant recognition to masker spectrum level were similar within subject pairs, whereas, in some cases, slopes of functions relating consonant recognition to speech level were shallower for hearing-impaired subjects than for their normal-hearing counterparts. Although greater improvement in consonant recognition with speech level was predicted for hearing-impaired than for normal-hearing subjects, on average, less improvement with speech level was observed. Shallower slopes of functions relating score to speech level observed for some hearing-impaired listeners may result from more shallow growth of speech sensation levels in spectral regions above the low-pass masker.

Frequency selectivity and consonant recognition for hearing-impaired and normal-hearing listeners with equivalent masked thresholds.

Thresholds in notched-noise maskers (NN) and narrow-band maskers (NB) were measured for normal-hearing and hearing-impaired subject pairs who were listening in a background of spectrally shaped broadband noise (SSBB). Consonant recognition was also measured in SSBB. SSBB was adjusted so that thresholds in that noise for each normal-hearing/hearing-impaired subject pair were equal. Threshold and signal-level differences between subject pairs were minimized with the addition of threshold-elevating SSBB, and the presence of a noise background for both groups provided a comparable listening environment for all subjects. At signal frequencies outside masker passbands, thresholds in NN and NB for hearing-impaired subjects were higher than for normal-hearing subjects, although threshold differences were much smaller than observed between normal-hearing and hearing-impaired subjects without SSBB. No consistent differences in consonant recognition measured in SSBB were observed between groups. The pattern of results is comparable to that observed in a previous experiment [Dubno and Schaefer, J. Acoust. Soc. Am. 91, 2110-2121 (1992)] in which thresholds in NN and NB, and consonant recognition, for hearing-impaired listeners were compared to results obtained for normal-hearing subjects, but only normal-hearing subjects listened in SSBB. Using a modified power-law model of masking additivity, thresholds in combined-masker conditions were estimated. Masking effects for spectrally overlapping maskers were similar for normal-hearing and hearing-impaired listeners and suggest that residual differences between subject groups are not due to the presence of an additional background noise.

Comparison of frequency selectivity and consonant recognition among hearing-impaired and masked normal-hearing listeners.

Frequency selectivity and consonant recognition were determined for normal-hearing and hearing-impaired listeners using techniques that facilitate comparisons of performance among listeners whose absolute thresholds vary in magnitude and configuration. First, for each of six subjects with cochlear hearing loss, masked thresholds in notched noise and narrow-band-noise maskers were obtained and compared to results for three normal-hearing listeners whose thresholds were precisely matched to the impaired listeners' by masking with spectrally shaped broadband noise. Second, for hearing-impaired listeners and their masked normal-hearing controls, measurements of consonant recognition were obtained at several speech-presentation levels selected on the basis of articulation-index predictions to assure equal speech-spectrum audibility across listeners. The results suggest that frequency selectivity is poorer for hearing-impaired listeners than for masked normal-hearing listeners, even when thresholds among subjects are equated, but the deviation from normal frequency selectivity is smaller than estimated from comparisons with normal-hearing listeners in quiet. Critical ratios for hearing-impaired listeners are equivalent to normal. Although frequency selectivity is reduced, there is no consistent difference in consonant recognition between hearing-impaired subjects and masked normal-hearing subjects, when performance is assessed under conditions that assure equal speech-spectrum audibility across subjects.

Minimal upward spread of masking: correlations with speech and auditory brainstem response masked thresholds.

Much less than predicted upward spread of masking, termed undermasking, was previously noted in three elderly listeners, who are the focus of this report. Three aspects of undermasking were studied: Reliability, facilitation of speech recognition in noise, and correlation with physiological measurements. The masker was a 90-dB-SPL 1-kHz low-pass-filtered noise. Reliability of undermasking was assessed from serial measurements made over an approximately 2-year interval. Masked speech thresholds were measured with an adaptive procedure for two types of stimuli: spondaic words and the California Consonant Test. Subjects with undermasking had substantially lower masked speech thresholds than either audiometrically matched elderly subjects or young, normal-hearing subjects. It appears that undermasking is a stable characteristic that provides the listener with exceptionally good communication abilities in noise. Finally, a strong positive correlation was observed between the masked auditory brainstem response (wave V) threshold and the masked behavioral threshold, suggesting that the mechanism producing undermasking is in the auditory periphery.

Masked thresholds and consonant recognition in low-pass maskers for hearing-impaired and normal-hearing listeners.

Thresholds and consonant recognition were measured in six low-pass maskers as a function of masker bandwidth for hearing-impaired subjects and for normal-hearing subjects listening in spectrally shaped broadband noise (SSBB). SSBB was adjusted such that thresholds in that masker for a normal-hearing listener were equal to a hearing-impaired listener's absolute thresholds. Thresholds measured in low-pass maskers were higher for hearing-impaired than for normal-hearing subjects for signal frequencies both within and outside masker passbands, although threshold differences were larger for signal frequencies outside masker passbands. Slopes of functions relating consonant recognition to speech level were not significantly different between groups, due to the presence of SSBB for the normal-hearing listeners. However, 25% of observed scores for hearing-impaired listeners, compared to only 5% of observed scores for normal-hearing listeners, were significantly poorer than predicted by the articulation index (AI), when AIs were computed using subjects' absolute thresholds. Better correspondence between observed and predicted scores in low-pass maskers was achieved when AIs were derived empirically from thresholds measured in each low-pass masker. Hence poorer-than-predicted consonant recognition scores in low-pass maskers were accounted for by higher-than-normal thresholds in those maskers.