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PubMed1988

Detection of ABR thresholds with a statistical synchrony measure.

Using the method of Fridman and his colleagues, a statistical test of auditory brainstem responses (ABR) for detecting auditory thresholds is presented. The synchrony measure (SM) which represents the degree of reproducibility for group averages was used to calculate the selected Fourier components of the group averages from phase variance. The sensitivity of the test was demonstrated on 35 normal ABRs with 60 and 45 dB SL stimulus intensity and in the absence of stimulus from the ipsilateral recordings. The SM of all cases of normal ABRs at 60 and 45 dB SL exceeded those in the absence of stimulation. The same procedure was applied to 16 ears with cochlear hearing loss with (4 ears) and without (10 ears) recruitment and 2 ears with relatively normal hearing threshold (less than 30 dB HL). Seven out of 10 ears without recruitment had the SM value at 60 dB SL stimulus intensity significantly lower than those of normal ABRs.

Adolescent↗
PubMed1988

A comparison of four methods of implementing automatic gain control (AGC) in hearing aids.

Hearing impairment of cochlear origin is usually associated with loudness recruitment. As a consequence, the dynamic range between threshold and the highest comfortable level is smaller than normal. To ensure that low-level sounds can be heard, while avoiding discomfort at high levels, a hearing aid with automatic gain control (AGC) is required. This paper compares four different systems for implementing AGC, and compares each of them with unaided listening and with linear amplification. The systems were evaluated by measuring thresholds for understanding speech in quiet and in five types of background sound: speech-shaped noise, 12-talker babble, cafeteria noise, traffic noise and a single competing speaker. The first system used a new dual-action AGC (called dual front-end AGC) operating on the whole speech signal. A slow-acting control voltage (recovery time 5 s) held the average level of speech at the output constant, regardless of the input level. In response to sudden intense transients, a fast-acting control voltage (recovery time 150 ms) reduced the gain rapidly and then returned the gain to the value set by the slow-acting component. In the second system, referred to as the mark II aid, the output of the dual front-end AGC was split into two frequency bands, and fast-acting (syllabic) compression was applied in the high-frequency band only. The bands were then recombined. The third system resembled the mark II aid except that fast-acting compression was applied in both bands. The fourth system resembled the 2-channel aid evaluated in previous trials (Moore, 1987). It was similar to the third system, but had only single-action front-end AGC with a recovery time of 400 ms. Six subjects with moderate sensorineural hearing loss accompanied by recruitment were used. Best results overall were obtained using the mark II aid. Speech reception thresholds (SRTs) in noise were, on average, 4 dB better than for linear amplification and 2.4 dB lower than for the previous 2-channel aid. There was a significant advantage of having fast-acting AGC in the high-frequency band, but no advantage of having AGC in the low-frequency band.

Acoustics↗
PubMed1993

Correcting for factors affecting ABR wave V latency.

The latency of auditory brainstem response (ABR) wave V has been shown to be affected by several subject and technical factors. Previous studies have often concluded with a recommendation to account or correct for one or more of these factors when latency is used as a means of detecting retrocochlear dysfunction. This study investigated the effect of subject age, sex, hearing loss and stimulus intensity on ABR wave V latency in a group of 189 clinical subjects in whom retrocochlear disease was effectively excluded. Regression analysis showed that all four factors exerted a significant influence on latency and that hearing loss and intensity were most effectively represented when combined to form a sensation level variable, together with a measure of audiogram slope.

Acoustic Stimulation↗
PubMed1994

Comparison of measures of frequency resolution and recruitment in patients undergoing neuro-otological investigation.

Loudness recruitment and reduced frequency resolution both occur in cochlear types of hearing loss. One theory of loudness recruitment suggests that, as intensity is coded partly by spread of excitation across the nerve fibre array, recruitment is a direct consequence of the broad spread of excitation associated with poor frequency resolution. The present study investigated the relationship between these two quantities. The study involved a simple measure of frequency resolution (three-point psychoacoustical tuning curve, PTC) and conventional measures of recruitment obtained from patients undergoing neuro-otological investigation. Results from 376 ears of 226 patients without any material conductive impairment are presented. Measures of recruitment included the alternate binaural loudness balance test (ABLB) and estimates of dynamic range given by the sensation levels of the uncomfortable loudness level and the acoustic reflex threshold. Once covariation with hearing threshold level had been accounted for, no clear relationship emerged between frequency resolution and any of the measures of recruitment. This finding does not support the notion that frequency resolution and recruitment are specifically related. Rather, PTCs provide information complementary to measures of recruitment.

Adolescent↗
PubMed1995

Simulation of the effects of loudness recruitment on the intelligibility of speech in noise.

This experiment simulated the threshold elevation and loudness recruitment associated with three different types of hearing loss: moderate flat (condition R2), severe flat (condition R3), and moderate-to-severe sloping (condition RX). This was done to allow an examination of the effects of these factors on the intelligibility of speech, in isolation from other factors that are normally associated with cochlear hearing loss, such as reduced frequency selectivity. The speech was presented at a fixed input level of 65 dB SPL, against a background of a noise whose spectrum was shaped to match the long-term average spectrum of the speech. The level of the background noise varied from 65 to 74 dB SPL. The simulation was performed by splitting the input signal into 13 frequency bands, and processing the envelope in each band so as to create loudness sensations in a normal ear that would resemble those produced in an impaired ear with recruitment. The bands were then recombined. All tests were performed using subjects with normal hearing. The simulation of hearing loss produced decrements in performance. The speech in condition R3 was inaudible. For conditions R2 and RX, the speech-to-noise ratios had to be up to 6 dB higher than in the control condition (R1, unprocessed stimuli) to achieve similar levels of performance. When linear amplification according to the NAL prescription was applied before the simulation, performance improved markedly for conditions R2 and RX, and did not differ significantly from that for R1. For condition R3, performance with simulated NAL amplification remained below that for condition R1; the decrement in performance was equivalent to about a 1 dB change in speech-to-noise ratio. The results of the present experiment show much smaller decrements in performance than those of an earlier experiment using a single talker as the interfering sound (Moore and Glasberg, 1993). It appears that loudness recruitment and threshold elevation have larger effects for a fluctuating background sound than for a steady background sound, and linear amplification is more effective in the latter case.

Acoustic Stimulation↗
PubMed1997

Comparison of real and simulated hearing impairment in subjects with unilateral and bilateral cochlear hearing loss.

Simulations of hearing impairment were presented to the normal ears of subjects with moderate to severe unilateral cochlear hearing loss. The intelligibility of speech in quiet and in background sounds was compared with that obtained for the impaired ears using unprocessed stimuli. The results of loudness matches between the two ears were used to tailor a simulation of threshold elevation combined with loudness recruitment individually for each subject. This was assessed either alone, or in combination with a simulation of reduced frequency selectivity, performed by spectral smearing. Finally, we included a simulation of 'dead' regions in the cochlea, where there are assumed to be no functioning inner hair cells and/or neurones, by band-stop filtering over the frequency range corresponding to the dead region. Performance for the impaired ears was markedly worse than for the normal ears using the simulation of threshold elevation and loudness recruitment. The addition of the simulation of reduced frequency selectivity caused performance to worsen, but it remained above that for the impaired ears. The additional simulation of a dead region had little effect, except for one subject, for whom it produced performance comparable to that for the impaired ear in quiet but not when background sounds were present. It is suggested that the relatively poor results for the impaired ears may be caused partly by a form of 'neglect' which is specific to subjects with unilateral or asymmetric loss. This idea was supported by results obtained using bilaterally hearing-impaired subjects, which were markedly better than for the impaired ears of the unilaterally hearing-impaired subjects, and comparable to those for the normal ears listening to the combined simulation of threshold elevation, loudness recruitment and reduced frequency selectivity.

Aged↗
PubMed1997

Effects of fast-acting high-frequency compression on the intelligibility of speech in steady and fluctuating background sounds.

This study examines whether speech intelligibility in background sounds can be improved for persons with loudness recruitment by the use of fast-acting compression applied at high frequencies, when the overall level of the sounds is held constant by means of a slow-acting automatic gain control (AGC) system and when appropriate frequency-response shaping is applied. Two types of fast-acting compression were used in the high-frequency channel of a two-channel system: a compression limiter with a 10:1 compression ratio and with a compression threshold about 9 dB below the peak level of the signal in the high-frequency channel; and a wide dynamic range compressor with a 2:1 compression ratio and with the compression threshold about 24 dB below the peak level of the signal in the high-frequency channel. A condition with linear processing in the high-frequency channel was also used. Speech reception thresholds (SRTs) were measured for two background sounds: a steady speech-shaped noise and a single male talker. All subjects had moderate-to-severe sensorineural hearing loss. Three different types of speech material were used: the adaptive sentence lists (ASL), the Bamford-Kowal-Bench (BKB) sentence lists and the Boothroyd word lists. For the steady background noise, the compression generally led to poorer performance than for the linear condition, although the deleterious effect was only significant for the 10:1 compression ratio. For the background of a single talker, the compression had no significant effect except for the ASL sentences, where the 10:1 compression gave significantly better performance than the linear condition. Overall, the results did not show any clear benefits of the fast-acting compression, possibly because the slow-acting AGC allowed the use of gains in the linear condition that were markedly higher than would normally be used with linear hearing aids.

Adult↗
PubMed1996

Binaural release from temporal induction.

This study examined the effects of interaural phase difference (IPhD) relations in temporal induction (TI)-that is, the perceived continuity of a fainter sound (inducee) through an interrupting higher amplitude sound (inducer). The extent of TI was measured both directly as the upper amplitude level for continuity and indirectly as the loudness reduction of the inducer. It was found that TI was inhibited when the IPhD of the inducer and the IPhD of the inducee differed. It was also found that the extent of induction was positively related to the masking potential of the inducer as measured by the binaural masking level difference procedure. These results suggest that TI involves processes that are affected by interaural phase differences and that the masking potential rule, shown by previous studies to apply in the frequency domain, applies also in the IPhD domain. The present findings are consistent with the hypothesis that TI results from allocation of a portion of the neural excitation produced by the inducer over to the inducee if the inducer has the appropriate masking potential. As a consequence, obliterated signals can be selectively restored on the basis of both frequency-specific monaural cues and azimuth-related binaural cues, abilities that can enhance detection of signals under the noisy conditions of everyday life.

Adult↗
PubMed1989

Partial masking in electrocutaneous sensation: a model for sensation matching, with applications to loudness recruitment.

A model for partial masking and other threshold-elevation effects is presented in the context of a sensation-matching paradigm. The model is applied to an electrocutaneous experiment in which the subjects adjusted stimulus intensity on the right-hand fingertip to match sensation levels of standard stimuli presented to the left fingertip. Concurrent mechanical stimulation on the right fingertip masked sensation magnitude in a way consistent with the model. Similarities between this tactile masking effect and analogous auditory phenomena are explored. When applied to loudness matching, the model describes the general shape of loudness contours and it shows that the steep slopes observed in auditory masking and "recruitment" can be a consequence of a threshold shift alone, without a supranormal growth in loudness. The model also shows that a small response bias can distort plots of sensation matching, leading to the suggestion that some varieties of loudness recruitment may not have a sensory basis.

Discrimination Learning↗
PubMed1989

Dichotic, diotic, and monaural summation of loudness: a comprehensive analysis of composition and psychophysical functions.

In a series of six experiments, the method of magnitude estimation, constrained by a multivariate model, was used to assess the rules that govern the summation of the loudness of two-tone complexes. This methodology enabled us to specify the amounts of summation and simultaneously to construct the corresponding loudness scales. The components had different frequency separations and in the different experiments were presented (1) dichotically, a different frequency to each ear; (2) diotically, to both ears; and (3) monaurally. Results replicated and in some conditions extended known features of multiple signal processing by the auditory system. Thus, qualitatively different rules of loudness integration appeared. For monaural and diotic modes of stimulation, overall loudness depended on total sound energy within the critical band, but on the simple sum of component loudnesses beyond the critical band. For dichotic presentations, a fully additive rule of loudness summation appeared, regardless of frequency spacing. For the latter (but not the former), loudness summation was perfect, with the underlying loudness scales closely approximating Stevens's sone scale.

Attention↗
PubMed2000

The perception of waning signals: decruitment in loudness and perceived size.

When a tone or broad-band noise sweeps smoothly from a moderate intensity to a low one, the loudness at the end of the sweep is far less than what would be predicted from its intensity. The accelerated reduction in loudness, which was first reported by Canévet (1986) and confirmed in several later reports, has been called loudness decruitment, and has been tentatively interpreted as the result of some form of adaptation. Since both simple and induced adaptation have distinctive temporal profiles, we undertook a series of studies in which we varied the duration of a tone whose intensity was continuously changing, to see whether the effect of duration on decruitment resembled the effects of duration on adaptation. We discovered that the magnitude of decruitment remained unaffected when the duration of the sweep was reduced far below the durations of 90 to 180 sec that have been used in previous studies. The same effect was observed for durations of around 20 sec, but it declined rapidly to a low level at the lowest duration of 1.0 sec. This temporal pattern is strikingly different from what has been reported for either simple or ipsilaterally induced adaptation, which suggests that neither form of adaptation can account for the entire effect. We also wanted to know whether an analogous phenomenon could exist for a sensory modality other than hearing. In the present study, observers were asked to judge the apparent size of a solid disk on a computer monitor, the disk increased or decreased continuously in area, or appeared as a series of separate areas, either in random order or in ordered progressions. We found that, as in the case of loudness, apparent size decreased more rapidly when the areas decreased continuously than would have been predicted from the actual areas themselves. We also found that some part of the accelerated shrinkage was due to a response bias in the observers' judgments that stemmed from knowledge that every value in a continuously changing series is predictably smaller (or larger, for a growing series). Whether the remaining part of the effect is a sensory phenomenon is an important issue for future research.

Adolescent↗
PubMed2005

Estimates of loudness, loudness discomfort, and the auditory dynamic range: normative estimates, comparison of procedures, and test-retest reliability.

The purpose of this series of experiments was to establish normative reference values for absolute and relative judgements of loudness discomfort and for the auditory dynamic range (DR), and to evaluate intersubject variability and intra-subject test-retest reliability for the respective measures of loudness discomfort. To establish the normal auditory DR, audiometric thresholds and loudness discomfort levels (LDLs) were measured from a group of 59 normal-hearing adults without sound tolerance problems. The resulting estimates of the LDL and DR were on the order of 100 dB HL and 95 dB, respectively. A subset (n = 18) of this larger group participated in further studies in which loudness growth functions and the upper limit of the auditory DR were measured by categorical scaling judgments. The findings revealed no significant differences between the test methods for absolute (LDL) and relative (categorical scaling) judgements of loudness discomfort, intersubject variability, or intrasubject test-retest reliability, and suggest that the simple LDL estimate of loudness discomfort is an efficient and valid clinical measure for characterizing the "threshold of discomfort."

Adult↗
PubMed1999

Clinical relevance of medial efferent auditory pathways.

Evoked otoacoustic emissions have been shown to be suppressed by sounds applied in the contralateral ear and this effect can be largely explained by the involvement of medial olivocochlear efferent fibers. Thus, EOAE recording during contralateral stimulation provides a non-invasive means of investigating auditory efferent system functioning in humans. The question remains, however, as to whether this test provides a tool, which could be useful in a variety of clinical applications. This review describes current clinical applications for this test, showing that it may prove useful for improving identification of retrocochlear pathologies. Some new areas are also identified. Methodological topics are discussed and suggestions for maximizing the value of this test are proposed.

Adult↗
PubMed2000

Audiological problems in patients with tinnitus exposed to noise and vibrations.

Tinnitus is a hearing sensation appearing without available sound fluctuations in the external environment. It is one of the major, constant and earliest symptoms suggesting different pathology of the hearing analyser. It must be considered, though, that it is evidenced also at disturbed functions of other organs and systems of the organism. The aim of the present study is to elucidate the state of the hearing analyser in patients with tinnitus occupationally exposed to noise and vibrations in relation to therapy. The study was performed on 67 miners, aged 34-55, mean age 44.5 years. The workers with subjective tinnitus (29 persons--43% of the studied group) are the object of this investigation. They were subjected to the following tests of the hearing analyser: pure tone audiometry; above-threshold audiometry (Carhardt's adaptation test, Lusher's differential threshold, SISI test, Kietz test. The evidence reveals that the studied group of workers occupationally exposed to noise, vibrations, dust, toxic substances etc. complain predominantly of tinnitus. It is accompanied by vertigo, headache and disturbed balance. Changes in the hearing function are observed; manifested by different degree of hypacusia concerning air and bone conductivity in the pure tone audiometry. The above-threshold tests also evidence deviations suggesting disturbed hearing function. These changes can be explained by mechanical-toxic pathogenic mechanisms leading to cerebral and vestibular dysfunction most probably of vascular-circulatory type manifested by the above stated deviations. The results are the basis for the following conclusions: 1. The anamnestic profile of workers with tinnitus exposed to noise and vibrations shows a prevalent percentage of vertigo, followed by headache and disturbed balance. 2. The otoneurological profile shows changes in the air and bone conductivity manifested by different degree of hypacusia. 3. The evaluation of the above-threshold tests also confirms the evidence of disturbed hearing function. 4. The relevant therapeutical approach has to be elaborated, having in mind the existing suggestion about the mechanical-toxic etiopathogenesis of the developed process of vascular-circulatory type.

Adult↗
PubMed2001

[Detection of the central hearing defects in persons exposed to industrial noise by duration of the rise and fall of sound signals].

Hearing was studied using speech, audiometer MA-31 and rise and fall of loudness in 365 workers exposed to industrial noise only and 86 workers exposed to noise and dust containing lead. Identification of the front of growing loudness was impaired more in persons exposed to lead-containing dust; therefore they have more serious central hearing defects.

Adolescent↗
PubMed1998

[The relationship between loudness recruitment phenomenon and distortim product otoacoustic emission and their clinical significance].

OBJECTIVE: To study the relationship between loudness recruitment and abnormal cochlear mechanism. METHODS: The basic properties of input/output (I/O) of distortion product otoacoustic emission (DPOAE) in 20 normal subjects(40 ears) and 50 cases with cochlear deafness (63 ears) with positive recruitment were studied and analyzed. RESULTS: Average slope of I/O at different frequencies in all deaf ears with recruitment was greater than those in the normal subjects with a statistical significance (P < 0.01). Moreover, thresholds of DPOAE in the recruitment positive ears were higher than those in normal subjects. CONCLUSION: Loudness recruitment and abnormal cochlear active mechanism are specially related. I/O functions of DPOAE are more perceptive and precise to appraise cochlear active mechanism. It probably may become a valuable test for early diagnosis of cochlear deafness.

Adolescent↗