Effects of cochlear impairment and equivalent-threshold masking on psychoacoustic tuning curves.

Psychoacoustic tuning curves in simultaneous masking were measured in three groups: listeners with hearing impairment of primarily cochlear origin, normal listeners with equivalent-threshold masking (ETM) and normal listeners tested in the quiet. ETM was produced by presenting a continuous back-ground noise that was spectrally shaped to yield masked thresholds within 3 dB of each impaired listener's quiet thresholds. For the tuning curves, the level of a 50-Hz-wide noise band necessary to mask a 10-dB SL tone was measured for six masker frequencies. Results under ETM indicate that the shape of the tuning curve depends not only on masked threshold at the probe frequency but also on the spectral shape of the masker. Tuning curves are abnormally broad in some impaired listeners even when the effects of their elevated thresholds, audiometric configuration and altered intensity perception are taken into account by comparisons with normal listeners with ETM.     

Estimating audiometric thresholds using auditory steady-state responses

Human auditory steady-state responses (ASSRs) were recorded using stimulus rates of 78-95 Hz in normal young subjects, in elderly subjects with relatively normal hearing, and in elderly subjects with sensorineural hearing impairment. Amplitude-intensity functions calculated relative to actual sensory thresholds (sensation level or SL) showed that amplitudes increased as stimulus intensity increased. In the hearing-impaired subjects this increase was more rapid at intensities just above threshold ("electrophysiological recruitment") than at higher intensities where the increase was similar to that seen in normal subjects. The thresholds in dB SL for recognizing an ASSR and the intersubject variability of these thresholds decreased with increasing recording time and were lower in the hearing impaired compared to the normal subjects. After 9.8 minutes of recording, the average ASSR thresholds (and standard deviations) were 12.6 +/- 8.7 in the normal subjects, 12.4 +/- 11.9 dB in the normal elderly, and 3.6 +/- 13.5 dB SL in the hearing-impaired subjects.     

Brain stem response audiometry at speech frequencies

Auditory-evoked brain stem response (BSR; wave V) was studied, using tone pips at three speech frequencies (500, 1 000 and 2 000 Hz) as stimuli. The tone pips consisted of 5-ms rise-decay times without a plateau. BSR recordings were made in 10 normal subjects and in 16 subjects with impaired hearing. In the normal subjects, BSR thresholds ranged from 10 to 20 dB SL at these three frequencies. In the subjects with impaired hearing, BSR thresholds corresponded well to conventional pure-tone thresholds at each frequency in cases of low- as well as high-frequency hearing loss. In all subjects with impaired hearing, the BSR thresholds were higher by as much as 25 dB than the pure-tone thresholds. The mean differences between these two thresholds at 500, 1 000 and 2 000 Hz were 11.3 ± 8.0, 10.9 ± 6.2 and 10.9 ± 7.3 dB, respectively.

Thus, we conclude that the BSR is useful for objective assessment of hearing thresholds at each of these speech frequencies.     

Ipsilateral acoustic reflex stimulation in normal and sensorineural impaired ears: a preliminary report.

Ipsilateral acoustic reflex thresholds were measured at 1,000 Hz and 2,000 Hz in 38 subjects with normal hearing and in 107 subjects with a symmetrical sensorineural hearing loss. Acoustic reflex thresholds were approximately six dB better for ipsilateral vs. contralateral stimuli for both subject groups. High ipsilateral reflex thresholds were associated with larger static compliance values in the sensorineural hearing impaired subjects. Reversed reflexes (increasing compliance with muscle contraction) were observed for ipsilateral stimulation in five per cent (two) of the normal hearing subjects, and 23 percent (25) of the sensorineural hearing impaired subjects. The number of reversed reflexes was greater for subjects with higher hearing thresholds and higher ipsilateral acoustic reflex thresholds. The results suggest that quantitative use of the ipsilateral acoustic reflex requires additional research. At present it seems prudent to use ipsilateral acoustic reflex measurements as a qualitative rather than a quantitative tool, e.g. in confirming the status of one middle ear when the other has a conductive hearing loss. However, even this limited role has a considerable clinical potential.     

Frequency selectivity in patients with acoustic neuroma

Frequency selectivity was compared in subjects with hearing loss due to acoustic neuroma and cochlear pathology, and normal listeners. A particular interest was the role of probe tone parameters on the shape of the tuning curve. Psychophysical tuning curves (PTCs) were measured for each of two equal energy 2000-Hz probe tones (10 dB SL/300 msec and 17 dB SL/60 msec), using simultaneous 1/3-octave narrowband noise maskers centered at 1, 1.25, 1.6, 2.5, 3.15, and 4 kHz. The results showed that the critical masker levels obtained for impaired listeners were significantly greater than those from normal subjects. The slope of the low-frequency limb of the PTC was steeper for normal compared to hearing-impaired listeners but there was no difference due to site of lesion. In all three groups, the critical masker levels obtained with the short probe were significantly greater than those for the long probe, negating the hypothesis that equal energy probes would yield the same outcomes. Tuning in listeners with hearing loss was highly correlated with audiometric threshold but not with tumor size, width of the internal auditory canal, or tumor location within the cerebellopontine angle. The main conclusion was that cochlear and retrocochlear hearing loss are similar with respect to their effect on frequency selectivity.     

Reliability of threshold, slope, and PB max for monosyllabic words

The Auditec recordings of the CID W-22 monosyllables were used to generate test and retest intelligibility functions on normally hearing listeners and subjects with mild-to-moderate sensorineural hearing loss. The normally hearing subjects were tested with 50-word lists at SPLs ranging from 15 to 50 dB. Lists of 25 words were used with the hearing-impaired group. The functions were analyzed to assess the reliability of threshold (50% point), slope (20%-80% points), and maximum intelligibility (PB max). The 50% point was obtained at 28 dB SPL for the normally hearing listeners and at a sensation level (SL) of 12 dB respondaic thresholds for the hearing-impaired group. Very stable monosyllabic thresholds were found because 95% of the test-retest values were within 6 dB for both subject groups. Slopes of 4.9% per dB and 2.7% per dB were obtained for the normally hearing and hearing-impaired groups, respectively. Fair reliability was observed; 95% of the test-retest values encompassed a range of +/- 1.9% per dB for the normally hearing subjects and +/- 1.1% per dB for the hearing-impaired group. Although group slopes provide useful information for selecting the range and step size for generating psychometric functions, the value of routinely obtaining slope on an individual basis has not been demonstrated. Even though the same word lists were used for both test and retest measurements, reliability closely agreed with predicted results based on the binomial theorem. In contrast to the large variability for a single list of 25 words, very stable PB max scores were found when two or three scores were averaged on the plateau of the function.     

Growth of Loudness in Listeners with Cochlear Hearing Losses: Recruitment Reconsidered

This article examines how loudness grows with increasing intensity near threshold in five listeners with hearing losses of predominantly cochlear origin. It provides evidence against the pervasive and long-held notion that such listeners show abnormally rapid loudness growth near their elevated thresholds. As in a previous study for listeners with normal hearing, loudness functions near threshold were derived from loudness matches between a pure tone and four- or ten-tone complexes using a simple model of loudness summation. This study assumed that the loudness function had the same form for any component of a complex, but a scale factor that depended on the amount of hearing loss allowed the loudness at threshold to vary with frequency. The best-fitting loudness functions had low-level local exponents [i.e., slopes of the low-level loudness function plotted as log(loudness) versus log(intensity)] that were within the normal range. At 0 dB SL, the average local exponents were 1.26 for the listeners with hearing losses compared with 1.31 for normal listeners, which indicates that loudness near threshold grows at similar rates in normal listeners and listeners with hearing losses. The model also indicated that, on average, the loudness at threshold doubled for every 16 dB of hearing loss. The increased loudness at threshold, together with somewhat enlarged local exponents around 20 dB SL, accounts for the near-normal loudness often obtained for high-SPL tones in listeners with hearing losses. Such loudness functions are consistent with the steep functions shown by classical data on loudness matches between tones for which thresholds are normal and tones for which thresholds are elevated. Thus, the present data indicate that an abnormally large loudness at an elevated threshold is likely to be a better definition of recruitment than the classical definition of it as an abnormally rapid growth of loudness above an elevated threshold.     

Auditory-filter characteristics for listeners with real and simulated hearing impairment

Functional simulation of sensorineural hearing impairment is an important research tool that can elucidate the nature of hearing impairments and suggest or eliminate compensatory signal-processing schemes. The objective of the current study was to evaluate the capability of an audibility-based functional simulation of hearing loss to reproduce the auditory-filter characteristics of listeners with sensorineural hearing loss. The hearing-loss simulation used either threshold-elevating noise alone or a combination of threshold-elevating noise and multiband expansion to reproduce the audibility-based characteristics of the loss (including detection thresholds, dynamic range, and loudness recruitment). The hearing losses of 10 listeners with bilateral, mild-to-severe hearing loss were simulated in 10 corresponding groups of 3 age-matched normal-hearing listeners. Frequency selectivity was measured using a notched-noise masking paradigm at five probe frequencies in the range of 250 to 4000 Hz with a fixed probe level of either 70 dB SPL or 8 dB SL (whichever was greater) and probe duration of 200 ms. The hearing-loss simulation reproduced the absolute thresholds of individual hearing-impaired listeners with an average root-mean-squared (RMS) difference of 2.2 dB and the notched-noise masked thresholds with an RMS difference of 5.6 dB. A rounded-exponential model of the notched-noise data was used to estimate equivalent rectangular bandwidths and slopes of the auditory filters. For some subjects and probe frequencies, the simulations were accurate in reproducing the auditory-filter characteristics of the hearing-impaired listeners. In other cases, however, the simulations underestimated the magnitude of the auditory bandwidths for the hearing-impaired listeners, which suggests the possibility of suprathreshold deficits.     

The 500 Hz masking-level difference and word recognition in multitalker babble for 40- to 89-year-old listeners with symmetrical sensorineural hearing loss

The purpose of this study was to determine if performances on a 500 Hz MLD task and a word-recognition task in multitalker babble covaried or varied independently for listeners with normal hearing and for listeners with hearing loss. Young listeners with normal hearing (n = 25) and older listeners (25 per decade from 40-80 years, n = 125) with sensorineural hearing loss were studied. Thresholds at 500 and 1000 Hz were < or = 30 dB HL and < or = 40 dB HL, respectively, with thresholds above 1000 Hz < 100 dB HL. There was no systematic relationship between the 500 Hz MLD and word-recognition performance in multitalker babble. Higher SoNo and SpiNo thresholds were observed for the older listeners, but the MLDs were the same for all groups. Word recognition in babble in terms of signal-to-babble ratio was on average 6.5 (40- to 49-year-old group) to 10.8 dB (80- to 89-year-old group) poorer for the older listeners with hearing loss. Neither pure-tone thresholds nor word-recognition abilities in quiet accurately predicted word-recognition performance in multitalker babble.     

Comparing normal hearing and hearing-impaired subject's performance on the Northwestern Auditory Test Number 6, California Consonant Test, and Pascoe's High-Frequency Word Test

The Northwestern Auditory Test No. 6, the California Consonant Test, and Pascoe's High-Frequency Test were presented to two groups of listeners. One group consisted of 12 patients with normal hearing up to 2 kHz accompanied by a high-frequency loss. The second group consisted of persons with normal hearing. There were significant differences between the two groups of listeners in overall discrimination scores, among the four intensity levels (10, 20, 30, 40 dB) and the three speech discrimination tests. When the data from the hearing-impaired subjects were analyzed, it was found that these individuals obtained higher scores on the NU 6 material at 20, 30, and 40 dB SL when compared with the California Consonant Test and Pascoe's test. The results from the Newmann-Kuel multicomparison test indicated no statistical significance between the results of the California test and Pascoe's test; however, the distribution of scores at 40 dB was different. Results of this study suggested that the NU 6 test was not sufficiently sensitive to detect consonant confusions in individuals with high-frequency hearing loss.     

Effects of noise and reverberation on the precedence effect in listeners with normal hearing and impaired hearing

The purpose of this study was to determine the effects of reverberation and noise on the precedence effect in listeners with hearing loss. Lag burst thresholds (LBTs) for 4-ms noise bursts were obtained for 2 groups of participants: impaired hearing and normal hearing. Data were collected in reverberant and anechoic environments in quiet and noise, at sensation levels of 10, 20, 30, 40, and 50 dB. Results indicated a significant effect of reverberation on LBTs for both participant groups. LBTs increased with sensation level in the reverberant environment and decreased with increasing sensation level in the anechoic environment. There was no effect of hearing loss on LBTs. When the change in LBT due to noise was compared, the effect of noise depended on group and environment, with a greater effect of noise on the performance of listeners with impaired hearing. It is likely that the ability to fuse direct sounds and early reflections is degraded in listeners with impaired hearing and that this contributes to the difficulties experienced by these listeners in reverberation and noise.     

Temporal gap detection in sensorineural and simulated hearing impairments

The objectives of this study were to assess the effect of the configuration of a hearing loss on gap detection and to determine if hearing impairment affects temporal resolution, per se. The minimum detectable gap duration, MDG, in a low-pass (cut-off at 7 kHz) noise was measured monaurally as a function of sound pressure level in six listeners with normal hearing, seven with hearing impairments of primarily cochlear origin, and eight with impairments simulated by masking. The impaired listeners' MDGs at 80 and 90 dB vary from about 3.5 ms (equal to the normal MDG) to about 8 ms and show little correlation with their average HL. At lower levels, the MDG is enlarged for all impaired listeners owing to the decreased SL of the noise. Most of the enlargement of the MDG could be reproduced by presenting a normal listener with a masking noise spectrally shaped to simulate the impaired listener's audiogram. However, at high levels, some impaired listeners performed worse than their simulated-loss counterparts, indicating that temporal resolution per se may be reduced in some, but not all, impaired listeners.     

Spectral contributions to the benefit from spatial separation of speech and noise.

Speech recognition in noise improves when speech and noise sources are separated in space. This benefit has two components whose effects are strongest in different frequency regions: (1) interaural level differences (e.g., head shadow), which are largest at higher frequencies, and (2) interaural time differences, which have their greatest contribution at lower frequencies. Binaural interactions enhance the separation of signals from noise through the use of these interaural differences. Here, the benefit attributable to spatial separation was measured as a function of the low- and high-pass cutoff frequency of speech and noise. Listeners were younger adults with normal hearing, older adults with normal hearing, and older adults with hearing loss. Binaural thresholds for narrowband noises were measured in quiet and in a speech-shaped masker as a function of masker low-pass cutoff frequency. Speech levels corresponding to 50% correct recognition of sentences from the Hearing in Noise Test (HINT) were measured in a 65-dB SPL speech-shaped noise. Thresholds for narrowband noises and for speech were measured with two loudspeaker configurations: (1) signals and speech-shaped noise at 0 degrees azimuth (in front of the listener) and (2) signals at 0 degrees azimuth and speech-shaped noise at 90 degrees azimuth (at the listener's side). The criterion measure was spatial separation benefit, or the difference in thresholds for the two conditions. Benefit of spatial separation for unfiltered speech averaged 6.1 dB for younger listeners with normal hearing, 4.9 dB for older listeners with normal hearing, and 2.7 dB for older listeners with hearing loss. Benefit was differentially affected by low-pass and high-pass filtering, suggesting a trade-off of the contributions of higher frequency interaural level differences and lower frequency interaural timing cues. As expected, older listeners with hearing loss benefited little from the improved signal-to-noise ratios in the higher frequencies resulting from head shadow, but showed some benefit from lower frequency cues. Spatial benefit for older listeners with normal hearing was reduced relative to benefit for younger listeners. This result may be related to older listeners' elevated thresholds at frequencies above 6.0 kHz.     

The effects of speech presentation level on acceptance of noise in listeners with normal and impaired hearing.

PURPOSE: To compare the effects of speech presentation level on acceptance of noise in listeners with normal and impaired hearing. METHOD: Participants were listeners with normal (n = 24) and impaired (n = 46) hearing who were matched for conventional acceptable noise level (ANL). ANL was then measured at 8 fixed speech presentation levels (40, 45, 50, 55, 60, 65, 70, and 75 dB HL) to determine if global ANL (i.e., ANL averaged across speech presentation levels) or ANL growth (i.e., the slope of the ANL function) varied between groups. RESULTS: The effects of speech presentation level on acceptance of noise were evaluated using global ANLs and ANL growth. Results showed global ANL and ANL growth were not significantly different for listeners with normal and impaired hearing, and neither ANL measure was related to pure-tone average for listeners with impaired hearing. Additionally, conventional ANLs were significantly correlated with both global ANLs and ANL growth for all listeners. CONCLUSION: These results indicate that the effects of speech presentation level on acceptance of noise are not related to hearing sensitivity. These results further indicate that a listener's conventional ANL was related to his or her global ANL and ANL growth.     

Temporal Resolution of the Normal Ear in Listeners with Unilateral Hearing Impairment

Unilateral hearing loss (UHL) leads to an imbalanced input to the brain and results in cortical reorganization. In listeners with unilateral impairments, while the perceptual deficits associated with the impaired ear are well documented, less is known regarding the auditory processing in the unimpaired, clinically normal ear. It is commonly accepted that perceptual consequences are unlikely to occur in the normal ear for listeners with UHL. This study investigated whether the temporal resolution in the normal-hearing (NH) ear of listeners with long-standing UHL is similar to those in listeners with NH. Temporal resolution was assayed via measuring gap detection thresholds (GDTs) in within- and between-channel paradigms. GDTs were assessed in the normal ear of adults with long-standing, severe-to-profound UHL (N = 13) and age-matched, NH listeners (N = 22) at two presentation levels (30 and 55 dB sensation level). Analysis indicated that within-channel GDTs for listeners with UHL were not significantly different than those for the NH subject group, but the between-channel GDTs for listeners with UHL were poorer (by greater than a factor of 2) than those for the listeners with NH. The hearing thresholds in the normal or impaired ears were not associated with the elevated between-channel GDTs for listeners with UHL. Contrary to the common assumption that auditory processing capabilities are preserved for the normal ear in listeners with UHL, the current study demonstrated that a long-standing unilateral hearing impairment may adversely affect auditory perception—temporal resolution—in the clinically normal ear. From a translational perspective, these findings imply that the temporal processing deficits in the unimpaired ear of listeners with unilateral hearing impairments may contribute to their overall auditory perceptual difficulties.     

Reaction time to 1- and 4-kHz tones as a function of sensation level in listeners with normal hearing

OBJECTIVE: Measures of reaction time (RT) near threshold have been used to indicate whether listeners with hearing losses of primarily cochlear origin experience greater loudness at elevated thresholds than at normal thresholds. These measurements have been based on the assumption that RTs near threshold are not affected by stimulus frequency in the 1- to 4-kHz range. The present study tests this hypothesis. DESIGN: To gain an understanding of how RT is affected by frequency, RTs to 1- and 4-kHz tones were measured in 16 listeners with normal hearing across a wide range of sensation levels (SLs). RESULTS: Statistical analyses indicate that RTs are affected by frequency in some listeners. This effect is most common at low SLs but is also present at higher SLs. Learning effects could not account for the observed differences between RTs at the two frequencies. CONCLUSIONS: Although reaction time-especially at low levels-is affected by stimulus frequency in some listeners, the effect is not large enough to account for the differences in RTs measured in all listeners with impaired hearing in other studies.     

Upward spread of masking in normal and abnormal ears

Upward spread of masking was studied for normals and sensorineurally hearing-impaired subjects with high-frequency hearing loss. Hearing-impaired listeners were recruited in such a way as to present normal hearing on the frequency of the masker, that is a narrow band of noise centered at 1 000 Hz. Levels of the masker were set at 70, 80 and 90 dB, respectively. Results first indicated the presence of a relationship between masked and elevated absolute thresholds for a masker level of 70 dB. At masker levels of 80 and 90 dB, hearing-impaired listeners showed excessive upward spread of masking in spite of normal hearing sensitivity at the masker frequency: with 80 and 90 dB of noise, upward spread of masking grew, respectively, 2.6 and 1.6 times faster than in normals. Furthermore, excessive upward spread of masking was shown to progress as a function of hearing loss. Results were interpreted as additional evidence of abnormal frequency selectivity in sensorineurally hearing-impaired listeners.     

Netherlands' Society of Audiology

Δ_i and Δ_r repetitive stimuli superimposed on continuous 0.5-, 1- and 4-kHz carrier tones were administered to 20 normally hearing persons, 8 adults with sensorineural hearing loss, 10 adults with conductive hearing loss and 22 childrean subjected to evoked response audiometry (ERA) for assessment of hearing acuity. The intensity modulation depth ranged from +1 to 10 dB. In the subject with normal hearing and in the adult patients, three carrier tone levels were used whenever possible: 20, 40, and 60 dB SL. The frequency modulation depth ranged from –1 to –10% of the carrier tone frequency. The same leveles for the carrier tone were used: 20, 40, and 60 dB SL. With a carrier tone level of 20 dB SL, a clear-cut vertex responsewas noted in 80% of the teste carried out in the normal adults with 5-dB Δ_i stimuli and with Δ_r stimuli of –3 to –5% in magnitude; the same figure are valid for the patients with sensorineural and conductive hearing loss. The patients with sensorineural hearing loss showed a tendency to give vertex responses with lower Δ_i stimuli than subject with normal hearing. However, this difference was not statistically significant. According to our results, the children tested can be roughly divided into two groups, the first including subjects with responses to Δt stimuli of +5 and +10 dB and Δ_r stimuli of –5% and –10%; the second group including subjects with no clear-cut responses to these stimuli.     

Masking of tone bursts by modulated noise in normal, noise-masked normal, and hearing-impaired listeners

Threshold of 4.6-ms tone bursts was measured in quiet and in the presence of a 100% sinusoidally amplitude-modulated speech-shaped noise. For the modulated-noise conditions, the onset of the tone burst coincided either with the maximum or the minimum modulator amplitude. The difference in these two masked thresholds provided an indication of the psychoacoustic modulation depth, or the modulation depth preserved within the auditory system. Modulation frequencies spanning the modulation spectrum of speech (2.5 to 20 Hz) were examined. Tone bursts were 500, 1400, and 4000 Hz. Subjects included normal listeners, normal listeners with a hearing loss simulated by high-pass noise, and hearing-impaired listeners having high-frequency sensorineural hearing loss. Normal listeners revealed a psychoacoustic modulation depth of 30-40 dB for the lowest modulation frequencies which decreased to about 15 dB at 20 Hz. The psychoacoustic modulation depth was decreased in the normal listeners with simulated hearing loss and in the hearing-impaired listeners. There was general agreement in the data, however, for the latter two groups of listeners suggesting that the normal listeners with hearing loss simulated by an additional masking noise provided a good representation of the performance of hearing-impaired listeners on this task.     

Débordement de masquage normal et anormal sur les aigus

Upward Spread of Masking in Normal and Impaired Ears

Upward spread of masking was studied for normals and sensorineurally hearing-impaired subjects with high-frequency hearing loss. Hearing-impaired listeners were recruited in such a way as to present normal hearing on the frequency of the masker, that is a narrow band of noise centered at 1 000 Hz. Levels of the masker were set at 70, 80 and 90 dB, respectively. Results first indicated the presence of a relationship between masked and elevated absolute thresholds for a masker level of 70 dB. At masker levels of 80 and 90 dB, hearing-impaired listeners showed excessive upward spread of masking in spite of normal hearing sensitivity at the masker frequency: with 80 and 90 dB of noise, upward spread of masking grew, respectively, 2.6 and 1.6 times faster than in normals. Furthermore, excessive upward spread of masking was shown to progress as a function of hearing loss. Results were interpreted as additional evidence of abnormal frequency selectivity in sensorineurally hearing-impaired listeners.