Longitudinal changes in speech recognition in older persons

Recognition of isolated monosyllabic words in quiet and recognition of key words in low- and high-context sentences in babble were measured in a large sample of older persons enrolled in a longitudinal study of age-related hearing loss. Repeated measures were obtained yearly or every 2 to 3 years. To control for concurrent changes in pure-tone thresholds and speech levels, speech-recognition scores were adjusted using an importance-weighted speech-audibility metric (AI). Linear-regression slope estimated the rate of change in adjusted speech-recognition scores. Recognition of words in quiet declined significantly faster with age than predicted by declines in speech audibility. As subjects aged, observed scores deviated increasingly from AI-predicted scores, but this effect did not accelerate with age. Rate of decline in word recognition was significantly faster for females than males and for females with high serum progesterone levels, whereas noise history had no effect. Rate of decline did not accelerate with age but increased with degree of hearing loss, suggesting that with more severe injury to the auditory system, impairments to auditory function other than reduced audibility resulted in faster declines in word recognition as subjects aged. Recognition of key words in low- and high-context sentences in babble did not decline significantly with age.     

Speech-reception threshold in noise with one and two hearing aids

The binaural free-field speech-reception threshold (SRT) in 70-dBA noise was measured with conversational sentences for 24 hearing-impaired subjects without hearing aids, with a hearing aid left, right, and left plus right, respectively. The sentences were always presented in front of the listener and the interfering noise, with a spectrum equal to the long-term average spectrum of the sentences, was presented either frontally, from the right, or from the left side. For subjects with only moderate hearing loss, PTA (average air-conduction hearing level at 500, 1000, and 2000 Hz) less than 50 dB, the SRT in 70-dBA noise in both ears is determined by the signal-to-noise ratio even if only one hearing aid is used. For larger hearing losses the SRT appears to be partly determined by the absolute threshold. In conditions with a high noise level relative to the absolute threshold, in which case for both ears the SRT is determined by the signal-to-noise ratio, a second hearing aid, just as a monaural hearing aid, generally does not improve the SRT. However, in the case of a high hearing level, or a low noise level, in which a monaural hearing aid is profitable, the use of two hearing aids is even more profitable. In a separate experiment, acoustic head shadow was measured at the entrance of the ear canal and at the microphone location of a hearing aid. It appeared that, for a lateral noise source and speech frontal, the microphone position of behind-the-ear hearing aids has a negative effect on the signal-to-noise ratio of 2-3 dB.     

Recognition of nonsense syllables by hearing-impaired listeners and by noise-masked normal hearers

In the present study, speech-recognition performance was measured in four hearing-impaired subjects and twelve normal hearers. The normal hearers were divided into four groups of three subjects each. Speech-recognition testing for the normal hearers was accomplished in a background of spectrally shaped noise in which the noise was shaped to produce masked thresholds identical to the quiet thresholds of one of the hearing-impaired subjects. The question addressed in this study is whether normal hearers with a hearing loss simulated through a shaped masking noise demonstrate speech-recognition difficulties similar to those of listeners with actual hearing impairment. Regarding overall percent-correct scores, the results indicated that two of the four hearing-impaired subjects performed better than their corresponding subgroup of noise-masked normal hearers, whereas the other two impaired listeners performed like the noise-masked normal listeners. A gross analysis of the types of errors made suggested that subjects with actual and simulated losses frequently made different types of errors.     

Automated pure-tone threshold estimations from extrapolated distortion product otoacoustic emission (DPOAE) input/output functions

A promising approach to the prediction of pure-tone thresholds through the estimation of DPOAE thresholds by input/output functions was recently published by Boege and Janssen [J. Acoust. Soc. Am. 111, 1810-1818 (2002)]. On the basis of their results, a device that enables automated measurements of these thresholds was recently developed. The purpose of the current study was to evaluate the reliability of this instrument for the objective assessment of hearing loss in 101 ears with either normal hearing or with cochlear hearing loss of up to 50 dB HL. The median difference between pure-tone hearing and DPOAE thresholds was approximately 2 dB. For individual subjects, however, DPOAE thresholds differed from pure-tone thresholds by up to 40 dB. We find, therefore, that the clinical benefits of this method are probably limited.     

Differences in auditory performance between monaural and dichotic conditions. I: masking thresholds in frozen noise.

Thresholds of a 5-ms, 1-kHz signal were determined in the presence of a frozen-noise masker. The noise had a flat power spectrum between 20 Hz and 5 kHz and was presented with a duration of 300 ms. The following interaural conditions were tested with four listeners: Noise and signal monaural at the same ear (monaural condition, NmSm), noise and signal identical at both ears (diotic condition, NoSo), noise identical at both ears and signal monaural (dichotic condition, NoSm) and uncorrelated noise at the two ears and signal monaural (NuSm). The signal was presented at a fixed temporal position with respect to the frozen noise in all measurements and thresholds were determined for different starting phases of the carrier frequency of the signal. Variation of the carrier phase strongly influenced the detection in the diotic condition and the masked thresholds varied by more than 10 dB. The pattern of thresholds for the monaural condition was less variable and the thresholds were generally higher than for the diotic condition. The monaural-diotic difference for specific starting phases amounted to as much as 8 dB. Comparison measurements using running noise maskers revealed no such difference. This relation between monaural and diotic thresholds was further investigated with eight additional subjects. Again, monaural and diotic thresholds in running noise were identical, while in frozen noise, diotic thresholds were consistently lower than monaural thresholds, even when the ear with the lower NmSm threshold was compared. For the starting phase showing the largest monaural-diotic difference, the thresholds for NoSm lay between the monaural and the diotic values. At other starting phases, the NoSm threshold was clearly lower than both the NmSm and the NoSo threshold. One possible explanation of the observed monaural-diotic differences relates to contralateral efferent interaction between the right and the left hearing pathway. A prediction based on this explanation was verified in a final experiment, where frozen-noise performance for NmSm was improved by simultaneously presenting an uncorrelated running noise to the opposite ear.     

Apparent auditory deprivation effects of late onset: the role of presentation level

Silman and colleagues [J. Acoust. Soc. Am. 76, 1347-1362 (1984)] have reported an apparent effect of late auditory deprivation; this presents as loss of discrimination over time in the unaided ear of individuals using a single hearing aid fitted in middle age. In a replication of the basic effect, the influence of presentation level was examined in 24 monaurally aided subjects. The effect was reversed at presentation levels below about 75 dB SPL. The ear that is normally aided performs better at high presentation levels, while, at lower presentation levels, the converse is true. Thus it appears that a form of selective adjustment takes place in a particular part of the dynamic range, at least in ears with a dynamic range limited by a sensory hearing loss. If this interpretation is correct, there are important implications for research on perceptual learning and for the time course of evaluation in hearing aid provision.     

Temporal integration and compression near absolute threshold in normal and impaired ears

The decrease in absolute threshold with increasing stimulus duration (often referred to as "temporal integration") is greater for listeners with normal hearing than for listeners with sensorineural hearing loss. It has been suggested that the difference is related to reduced basilar-membrane (BM) compression in the impaired group. The present experiment tested this hypothesis by comparing temporal integration and BM compression in normal and impaired ears at low levels. Absolute thresholds were measured for 4, 24, and 44 ms pure-tone signals, with frequencies (f(s)) of 2 and 4 kHz. The difference between the absolute thresholds for the 4 and 24 ms signals was used as a measure of temporal integration. Compression near threshold was estimated by measuring the level of a 100 ms off-frequency (0.45f(s)) pure-tone forward masker required to mask a 44 ms pure-tone signal presented at sensation levels of 5 and 10 dB. There was a significant negative correlation between amount of temporal integration and absolute threshold. However, there was no correlation between absolute threshold and compression at low levels; both normal and impaired ears showed a nearly linear response. The results suggest that the differences in integration between normal and impaired ears cannot be explained by differences in BM compression.     

Hearing threshold estimation using concurrent measurement of distortion product otoacoustic emissions and auditory steady-state responses

Both distortion product otoacoustic emissions (DPOAEs) and auditory steady-state responses (ASSRs) provide frequency-specific assessment of hearing. However, each method suffers from some restrictions. Hearing losses above 50 dB HL are not quantifiable using DPOAEs and their performance at frequencies below 1 kHz is limited, but their recording time is short. In contrast, ASSRs are a time-consuming method but have the ability to determine hearing thresholds in a wider range of frequencies and hearing losses. Thus, recording DPOAEs and ASSRs simultaneously at their adequate frequencies and levels could decrease the overall test time considerably. The goal of the present study was to develop a parameter-setting and test-protocol to measure DPOAEs and ASSRs binaurally and simultaneously at multiple frequencies. Ten normal-hearing and 23 hearing-impaired subjects participated in the study. The interaction of both responses when stimulated simultaneously at frequencies between 0.25 and 6 kHz was examined. Two limiting factors need to be kept. Frequency distance between ASSR carrier frequency f(c) and DPOAE primary tone f(2) needs to be at least 1.5 octaves, and DPOAEs may not be measured if the ASSR stimulus level is 70 dB SPL or above. There was a significant correlation between pure-tone and DPOAE/ASSR-thresholds in sensorineural hearing loss ears.     

The effects of hearing loss on the contribution of high- and low-frequency speech information to speech understanding

The speech understanding of persons with "flat" hearing loss (HI) was compared to a normal-hearing (NH) control group to examine how hearing loss affects the contribution of speech information in various frequency regions. Speech understanding in noise was assessed at multiple low- and high-pass filter cutoff frequencies. Noise levels were chosen to ensure that the noise, rather than quiet thresholds, determined audibility. The performance of HI subjects was compared to a NH group listening at the same signal-to-noise ratio and a comparable presentation level. Although absolute speech scores for the HI group were reduced, performance improvements as the speech and noise bandwidth increased were comparable between groups. These data suggest that the presence of hearing loss results in a uniform, rather than frequency-specific, deficit in the contribution of speech information. Measures of auditory thresholds in noise and speech intelligibility index (SII) calculations were also performed. These data suggest that differences in performance between the HI and NH groups are due primarily to audibility differences between groups. Measures of auditory thresholds in noise showed the "effective masking spectrum" of the noise was greater for the HI than the NH subjects.     

Temporal processing in the aging auditory system.

Measures of monaural temporal processing and binaural sensitivity were obtained from 12 young (mean age = 26.1 years) and 12 elderly (mean age = 70.9 years) adults with clinically normal hearing (pure-tone thresholds < or = 20 dB HL from 250 to 6000 Hz). Monaural temporal processing was measured by gap detection thresholds. Binaural sensitivity was measured by interaural time difference (ITD) thresholds. Gap and ITD thresholds were obtained at three sound levels (4, 8, or 16 dB above individual threshold). Subjects were also tested on two measures of speech perception, a masking level difference (MLD) task, and a syllable identification/discrimination task that included phonemes varying in voice onset time (VOT). Elderly listeners displayed poorer monaural temporal analysis (higher gap detection thresholds) and poorer binaural processing (higher ITD thresholds) at all sound levels. There were significant interactions between age and sound level, indicating that the age difference was larger at lower stimulus levels. Gap detection performance was found to correlate significantly with performance on the ITD task for young, but not elderly adult listeners. Elderly listeners also performed more poorly than younger listeners on both speech measures; however, there was no significant correlation between psychoacoustic and speech measures of temporal processing. Findings suggest that age-related factors other than peripheral hearing loss contribute to temporal processing deficits of elderly listeners.     

Modeling sensorineural hearing loss. I. Model and retrospective evaluation

The present article describes an approach to the evaluation of psychoacoustic data from the hearing impaired. The results obtained from the hearing impaired in several studies of frequency resolution, temporal resolution, and speech recognition are compared to the results expected for noise-masked normal listeners. It is presumed in this approach that the hypothetical noise-masked normal listeners have masked thresholds that agree perfectly with the quiet thresholds of the hearing-impaired subjects. Using this approach, most of the results obtained from impaired ears on spectral-resolution and speech-recognition tasks could be accurately predicted, an exception being results from spectral-resolution paradigms using fixed-level signals. Some of the data from hearing-impaired listeners on temporal-resolution tasks, on the other hand, could not be adequately described with this approach. The latter data, however, were much more limited. Additional data are needed to better evaluate the adequacy of this approach in describing the performance of the hearing impaired on temporal-resolution tasks.     

Application of the articulation index to the speech recognition of normal and impaired listeners wearing hearing protection

The present study examined the application of the articulation index (AI) as a predictor of the speech-recognition performance of normal and hearing-impaired listeners with and without hearing protection. The speech-recognition scores of 12 normal and 12 hearing-impaired subjects were measured for a wide range of conditions designed to be representative of those in the workplace. Conditions included testing in quiet, in two types of background noise (white versus speech spectrum), at three signal-to-noise ratios (+ 5, 0, - 5 dB), and in three conditions of protection (unprotected, earplugs, earmuffs). The mean results for all 21 listening conditions and both groups of subjects were accurately described by the AI. Moreover, a single transfer-function relating performance to the AI could describe all the data from both groups.     

Forward-masked monaural and interaural intensity discrimination

Intensity-discrimination thresholds were measured for a 25-ms, 6-kHz pure tone for pedestal levels from 40 to 90 dB sound pressure level (SPL) with and without a forward masker (100-ms narrowband Gaussian noise, N(0)=70 dB). When the masker was present, the masker and probe were separated by 100 ms of silence. Unmasked and masked thresholds were measured in a two-interval monaural procedure and, separately, in a single-interval interaural procedure in which the pedestal and incremented pedestals were presented simultaneously to opposite ears. While the monaural thresholds were elevated markedly by the forward masker for mid-level pedestals, interaural thresholds were nearly unaffected by the masker across pedestal levels. The results argue against the notion that the monaural elevation in forward-masked thresholds is due to degraded encoding of intensity information at early stages of auditory processing.     

Relating binaural pitch perception to the individual listener's auditory profile

The ability of eight normal-hearing listeners and fourteen listeners with sensorineural hearing loss to detect and identify pitch contours was measured for binaural-pitch stimuli and salience-matched monaurally detectable pitches. In an effort to determine whether impaired binaural pitch perception was linked to a specific deficit, the auditory profiles of the individual listeners were characterized using measures of loudness perception, cognitive ability, binaural processing, temporal fine structure processing, and frequency selectivity, in addition to common audiometric measures. Two of the listeners were found not to perceive binaural pitch at all, despite a clear detection of monaural pitch. While both binaural and monaural pitches were detectable by all other listeners, identification scores were significantly lower for binaural than for monaural pitch. A total absence of binaural pitch sensation coexisted with a loss of a binaural signal-detection advantage in noise, without implying reduced cognitive function. Auditory filter bandwidths did not correlate with the difference in pitch identification scores between binaural and monaural pitches. However, subjects with impaired binaural pitch perception showed deficits in temporal fine structure processing. Whether the observed deficits stemmed from peripheral or central mechanisms could not be resolved here, but the present findings may be useful for hearing loss characterization.     

The effect of speech presentation level on measurement of auditory acclimatization to amplified speech

A systematic improvement in auditory performance over time, following a change in the acoustic information available to the listener (that cannot be attributed to task, procedural or training effects) is known as auditory acclimatization. However, there is conflicting evidence concerning the existence of auditory acclimatization; some studies show an improvement in performance over time while other studies show no change. In an attempt to resolve this conflict, speech recognition abilities of 16 subjects with bilateral sensorineural hearing impairments were measured over a 12-week period following provision of a monaural hearing instrument for the first time. The not-fitted ear was used as the control. Three presentation levels were used representing quiet, normal, and raised speech. The results confirm the presence of acclimatization. In addition, the results show that acclimatization is evident at the higher presentation levels but not at the lowest.     

Comparison of discomfort levels obtained with pure tones and multitone complexes

The relationship between threshold of discomfort (TD) estimates and the number of components in a complex signal has been investigated. The thresholds of discomfort were first obtained for 16 pure tones located at the center frequency of critical bands from 250 to 4000 Hz. Subsequently, thresholds of discomfort were obtained for 2, 4, 8, and 16 tone complexes. The pure-tone components of the complexes were systematically selected from the same 16 pure tones. For each subject, the relative intensities of the components in the four complexes were determined in such a way so as to parallel the pure tone TD contour obtained for that subject. Data were obtained from 15 normal and 15 hearing impaired adults. The individuals in the latter group all had mild to moderate sensorineural hearing loss. Summation of discomfort (S) was defined as the difference between the threshold of discomfort for a pure tone presented in isolation and within the complex. The two groups demonstrated different summation values. For both groups, however, the summation was shown to be a linear function of the logarithm of the number of components in the complex: S = a + b log (n) where n is the number of components (2, 4, 8, 16). For the normal hearing group, a and b are 2.05 and 11.51, respectively, while for the hearing impaired group, they are 3.95 and 12.88, respectively. While the future digital hearing aids can easily regulate their limiting levels so as to accurately account for this summation, present day hearing aids may underestimate this effect.(ABSTRACT TRUNCATED AT 250 WORDS)     

面向中频段听阈突变听力损失的非均匀滤波器组设计*

滤波器组是气传导助听器进行听觉补偿的重要功能模块。针对现有固定滤波器组对中频段听阈突变听损听力图的匹配效果欠佳问题,本文提出一种13子带非均匀滤波器组设计方案。不同于现有固定滤波器组,本文首先将全频段进行等比例三段划分,便于滤波器组在相应频段内进行听损补偿;然后在低频和高频段子带具有较高分布密度的前提下,适当增加中频段子带的分布密度,以提升中频段听损补偿效果;最后根据听力图的倍频特征点确定子带的中心频率,从而得到适配听力图的子带排布方案。此外,将频率响应掩蔽技术和奈奎斯特滤波器用于各子带的产生,进一步降低了滤波器组群延时和硬件复杂度。仿真分析表明,相比于现有16子带非均匀滤波器组,本文滤波器组对各类型中频段听阈突变听损听力图的平均匹配性能提升了48.4%,群延时降低了11.7%。因此,所设计滤波器组在面向补偿中频段听阈突变听损的气传导助听器中具有一定应用价值。     

Decline of speech understanding and auditory thresholds in the elderly

A group of 29 elderly subjects between 60.0 and 83.7 years of age at the beginning of the study, and whose hearing loss was not greater than moderate, was tested twice, an average of 5.27 years apart. The tests measured pure-tone thresholds, word recognition in quiet, and understanding of speech with various types of distortion (low-pass filtering, time compression) or interference (single speaker, babble noise, reverberation). Performance declined consistently and significantly between the two testing phases. In addition, the variability of speech understanding measures increased significantly between testing phases, though the variability of audiometric measurements did not. A right-ear superiority was observed but this lateral asymmetry did not increase between testing phases. Comparison of the elderly subjects with a group of young subjects with normal hearing shows that the decline of speech understanding measures accelerated significantly relative to the decline in audiometric measures in the seventh to ninth decades of life. On the assumption that speech understanding depends linearly on age and audiometric variables, there is evidence that this linear relationship changes with age, suggesting that not only the accuracy but also the nature of speech understanding evolves with age.     

Perception of sentences, words, and speech features by profoundly hearing-impaired children using a multichannel electrotactile speech processor

Fourteen prelinguistically profoundly hearing-impaired children were fitted with the multichannel electrotactile speech processor (Tickle Talker) developed by Cochlear Pty. Ltd. and the University of Melbourne. Each child participated in an ongoing training and evaluation program, which included measures of speech perception and production. Results of speech perception testing demonstrate clear benefits for children fitted with the device. Thresholds for detection of pure tones were lower for the Tickle Talker than for hearing aids across the frequency range 250-4000 Hz, with the greatest tactual advantage in the high-frequency consonant range (above 2000 Hz). Individual and mean speech detection thresholds for the Ling 5-sound test confirmed that speech sounds were detected by the electrotactile device at levels consistent with normal conversational speech. Results for three speech feature tests showed significant improvement when the Tickle Talker was used in combination with hearing aids (TA) as compared with hearing aids along (A). Mean scores in the TA condition increased by 11% for vowel duration, 20% for vowel formant, and 25% for consonant manner as compared with hearing aids alone. Mean TA score on a closed-set word test (WIPI) was 48%, as compared with 32% for hearing aids alone. Similarly, mean WIPI score for the combination of Tickle Talker, lipreading, and hearing aids (TLA) increased by 6% as compared with combined lipreading and hearing aid (LA) scores. Mean scores on open-set sentences (BKB) showed a significant increase of 21% for the tactually aided condition (TLA) as compared with unaided (LA). These results indicate that, given sufficient training, children can utilize speech feature information provided through the Tickle Talker to improve discrimination of words and sentences. These results indicate that, given sufficient training, children can utilize speech feature information provided through the Tickle Talker to improve discrimination of words and sentences. These results are consistent with improvement in speech discrimination previously reported for normally hearing and hearing-impaired adults using the device. Anecdotal evidence also indicates some improvements in speech production for children fitted with the Tickle Talker.     

Localization of virtual sound sources with bilateral hearing aids in realistic acoustical scenes

Sound localization with hearing aids has traditionally been investigated in artificial laboratory settings. These settings are not representative of environments in which hearing aids are used. With individual Head-Related Transfer Functions (HRTFs) and room simulations, realistic environments can be reproduced and the performance of hearing aid algorithms can be evaluated. In this study, four different environments with background noise have been implemented in which listeners had to localize different sound sources. The HRTFs were measured inside the ear canals of the test subjects and by the microphones of Behind-The-Ear (BTEs) hearing aids. In the first experiment the system for virtual acoustics was evaluated by comparing perceptual sound localization results for the four scenes in a real room with a simulated one. In the second experiment, sound localization with three BTE algorithms, an omnidirectional microphone, a monaural cardioid-shaped beamformer and a monaural noise canceler, was examined. The results showed that the system for generating virtual environments is a reliable tool to evaluate sound localization with hearing aids. With BTE hearing aids localization performance decreased and the number of front-back confusions was at chance level. The beamformer, due to its directivity characteristics, allowed the listener to resolve the front-back ambiguity.