Showing papers in "British Journal of Audiology in 1997"

Epidemiology of Permanent Childhood Hearing Impairment in Trent Region, 1985–1993

Abstract: This retrospective study of permanent childhood hearing impairment (PCHI) > or = 40 dB HL in children born between 1985 and 1993 and resident in Trent Health Region, achieved an ascertainment of 92.9% of that expected from previous studies and 100% for the subset of children born between 1985 and 1990. The prevalence rate of all permanent hearing impairment > or = 40 dB HL for the birth cohort 1985-90 is 133 (95% confidence interval, (ci) 122-145) per 100,000 live births (1 in 750). Sixteen per cent of PCHI were postnatally acquired, late-onset or progressive impairments. Excluding these, the prevalence rate for congenital impairments is 112 (ci 101-123) per 100,000 (1 in 900). The rate for profound impairments > or = 95 dB HL is 24 (ci 20-30) per 100,000 live births (1 in 4150). Prevalence was increased sixfold for children with a history of neonatal intensive care and 14-fold for children with a family history, compared with children with no risk factors. A more than two-fold increase in prevalence was seen in Asian children. For the congenitally-impaired children born between 1985 and 1990, 29% had a stay in neonatal intensive care > or = 48 hours, 30% had a family history of permanent childhood hearing impairment, and 12% had a cranio-facial abnormality (CFA). Over 59% were potentially detectable by a targeted neonatal screening programme using these three high-risk factors. For 1985-1993, the overall yield of the targeted neonatal screening programmes available in three of the 11 health districts was 15% but increased over time. The overall yield from the Health Visitor distraction test was 30% but lower in districts with neonatal screening programmes. Only 59% of children had a stated aetiology, classified by time of onset into genetic, including syndromes and CFA (41%), pre- or peri-natal (10%), post-natally acquired (6%), and uncertain onset (2%). Just under 40% of the children were said to have another clinical or developmental problem, about half of whom had at least two additional problems. The median age at referral, confirmation of the impairment, prescription of the hearing aid and fitting of the hearing aid were, respectively, 10.4 months, 18.1 months, 24.4 months and 26.3 months. A more severe impairment was associated with earlier age. Small improvements in the median age of hearing aid prescription and fitting were seen over time. Twenty-five per cent of children were referred for genetic counselling, the proportion increasing systematically with the severity of the impairment. Based on evidence of the yield from hearing screens we suggest a wider implementation of neonatal screening and further consideration of the role of the health visitor distraction test in the identification of children with PCHI. To facilitate further assessment of services for hearing-impaired children we suggest implementation of a co-ordinated shared list of children with permanent hearing impairment on a region-wide basis to provide adequate numbers for comparison over time, and the routine collection of a minimum set of data for each child.

Introduction to Wavelet Analysis

Abstract: Wavelet transform and multiresolution decomposition are described. Examples of the application of orthogonal wavelet transform to acoustic evoked potentials and otoacoustic emissions (OEA) are given and basic features of wavelet packets and wavelet network methods are characterized. An approach that enables the identification of local signal structures - a generalization of wavelet transform called Matching Pursuit - is presented. In the framework of this method the signal is decomposed into time-frequency ‘atoms', which offers a possibility of determination of an ‘instantaneous frequency’ with the accuracy close to the theoretical limit. The method is illustrated by application to OAE signals. The advantages and limitations of the methods presented are discussed.

The future of cochlear implants

Abstract: Remarkable progress has been made in recent years in the design and application of processing strategies for cochlear implants. Most notably, use of the new spectral peak (SPEAK) and continuous interleaved sampling (CIS) strategies have provided large improvements in speech reception performance compared with prior strategies (NIH Consensus Statement, 1995; Skinner et al., 1994a; Wilson et al., 1991). All major manufacturers of multichannel implant systems, including Advanced Bionics Corp., Bionic Systems, Cochlear Pty. Ltd., and Med El, now offer CIS or CIS-like strategies in their speech processors. The SPEAK strategy was developed by Cochlear Pty. Ltd and continues to be one of the options available in that company's devices. The principal purpose of this editorial is to present some of the many possibilities for further improvements in performance. To the extent that such possibilities are realized, implant systems of the future may be quite different from present systems, with different processing strategies, electrode designs, telemetry features, and fitting procedures.

Effect of Hearing Impairment on Educational Outcomes and Employment up to the Age of 25 Years in Northern Finland

Abstract: The association between hearing impairment in adolescence and school performance and the outcome of education was studied among 25-year-old subjects followed since pregnancy in the Northern Finland birth cohort. The series, 395 subjects with abnormal hearing and 977 randomly selected controls, was based on a questionnaire on hearing and school achievement sent to 11780 members of the cohort alive at the age of 14 years, and on audiometric screening test requested from health centers. Hearing loss was defined as 'clinically significant' if the pure tone average (PTA; mean of the thresholds at 0.5, 1 and 2 kHz) exceeded 25 dB in the better ear; a threshold of > or = 30 dB at 4 kHz and a PTA of < or = 25 dB as '4 kHz loss'; and as 'slightly abnormal' if any of the thresholds exceeded 20 dB at any frequency and the case did not belong to the above two categories. The more severe the hearing impairment, the poorer was the child's performance at elementary school. Those with normal hearing and those with a slightly abnormal or 4 kHz loss were equally often accepted for intermediate education (88%), while those with a clinically significant loss had the lowest acceptance figures (64%). When adjusting for neurological and social confounders, excluding mental disability, the risk of not qualifying from intermediate or higher education at all was twice as high among those with a clinically significant loss as among the controls (OR 2.1, 95% CI 1.13-3.8), and was still elevated after adjustment had been made for all the relevant perinatal, neurological and social factors (OR 1.9, 95% CI 1.02-3.6). 14% of those with a clinically significant hearing loss, 9% of the subjects with a 4 kHz loss and 7% of those with normal hearing were unemployed at the age of 25 years. Hearing impairment appears to have effects on both the outcome of education and employment status.

Audiological and psychological characteristics of a group of tinnitus sufferers, prior to tinnitus management training.

Abstract: A profile of audiological and psychological characteristics, obtained before starting tinnitus management training, is presented for 96 subjects with tinnitus. Variability was marked in all measures. A history of headaches, neck or back pain, or balance problems was not related to the ability to cope with tinnitus. The coping strategies used to manage tinnitus were influenced by the beliefs held about tinnitus, but the coping strategies chosen were not necessarily effective. No gender differences were found in coping ability or overall stress levels, although there were gender differences on some psychological measures and stress influences. Subjects who had previously sought assistance differed from those who had not in the complexity of the tinnitus sounds, the level of emotional reaction and the use of coping behaviours.

Hearing Aids: Past, Present, Future: Moving Toward Normal Conversations in Noise

Abstract: (1997). Hearing Aids: Past, Present, Future: Moving Toward Normal Conversations in Noise. British Journal of Audiology: Vol. 31, No. 3, pp. 141-148.

Risk factors for childhood sensorineural hearing loss in the Oxford Region

Abstract: We have used a comprehensive register of hearing-impaired children born in the former Oxford Health Region to study risk factors for sensorineural hearing loss. The occurrence of a wide variety of risk factors was documented from the case notes of 145 children; these were all the cases known at the time of the study with all degrees of hearing loss born between 1984 and 1988. Comparison with the normal Regional population showed that maternal age over 35 years and Asian ethnic origin were significant risk factors for congenital (non-acquired) hearing loss (odds ratio 1.7 and 2.5 respectively). Black/Asian children were also significantly more likely to have acquired losses. Low birthweight (below 2500 g) also gave a significantly increased risk, with an odds ratio of 4.5, rising to 9.6 for birthweight less than 1500 g. We also found that significantly more hearing-impaired cases were in lower social classes compared with the general population. A high proportion of cases (24%) had cranio-facial abnormalities (CFA), including many non-aural abnormalities and dysmorphic features, which therefore should be counted as high risk. Hearing losses acquired due to perinatal causes were almost all mild or moderate. Four factors-admission to special care baby unit for more than 72 hours, CFA, family history, and meningitis-accounted for 69% of all cases in this study. Targeted neonatal screening based on the first three factors, plus obligatory testing following meningitis, therefore, should be highly efficient at detecting deafness early.

Developmental Changes in Tympanometry: A Case Study

Abstract: The use of 226 Hz tympanometry in neonates and infants has been controversial due to the large number of false negative responses for middle ear pathology. A review of the literature highlights several anatomical differences between this population and that of the adult, which is not recognized during interpretation of their tympanograms. The aim of the study was to document tympanometric changes in a single child using 226 Hz, 1000 Hz and sweep frequency probe tones until she was 6.5 months old. Both 226 Hz and 1000 Hz tympanograms show a maturational change in middle ear resonance from a mass to a stiffness-dominated system, which was corroborated by sweep frequency probe tones. It is suggested that high-frequency probe tones were able to increase test sensitivity to the mechanics of the middle ear when it was mass-dominated, as in this infant. Due to the large intersubject variability reported in the literature, it is recommended that both high and conventional probe tone tympanograms are perfo...

A Randomized, Controlled Trial of the Efficacy of a Communication Course for First Time Hearing Aid Users

Abstract: Many centres include a communication course as part of their auditory rehabilitation. These usually take the form of a small group and include discussion of the effects of hearing loss, use of the hearing aid, hearing tactics and lip reading. To investigate the efficacy of such a rehabilitation programme a randomized, controlled trial of a communication course was undertaken. All subjects were first time hearing aid users; handicap was measured using the Quantified Denver Scale of Communication Function (QDS) at the time of hearing aid fitting, and then 13 weeks later. All subjects had a hearing aid follow-up appointment, but the treatment group (n = 22) also underwent a four-week communication course, while the control group (n = 25) had no further rehabilitation. The reduction in handicap measured by the change in QDS was significantly greater for the treatment group than for the control group (Mann Whitney U test, tied p value = 0.014). This indicates that such a communication course is efficacious in reducing handicap. Further research is required to identify the populations that will benefit most from such a course.

Behavioural and autonomic responses to sound in pre-term and full-term babies.

Abstract: The pattern of motor (body movement) and autonomic (heart rate and respiration) responses to no sound and sound trials were compared in 20 pre-term and 22 full-term neonates. Sound levels were calibrated using neonatal ear-sized couplers to produce, in the neonatal ear, sound levels of 80, 90 and 100 dB SPL. Accelerations in heart rate (> or = beats per minute for pre-terms; > or = 7 beats per minute for full-terms) were found to be the best criterion for establishing a possible response using bandpass noise at 80, 90 or 100 dB SPL. Respiration rate decreased in response to sound stimuli, this being significant for the pre-term group for the 100 dB SPL stimulus when comparing the 5 s period post-stimulus with the stimulus period. The number of movements detected during the sound trials was higher than for the control trials, being statistically significant for the pre-term group. These changes were elicited in response to stimuli presented at levels some 20-40 dB lower than for other studies and for behavioural screening because sounds were calibrated in an appropriately sized coupler. It is concluded that the response to sound is different in the pre-term group compared with the full-term group.

Normal and Hearing-Impaired Word Recognition Scores for Monosyllabic Words in Quiet and Noise

Abstract: The effects of noise on word recognition scores were assessed with normal-hearing and hearing-impaired subjects. Fifty-one normal-hearing subjects were tested at 50 dB HL using signal-to-noise ratios (S/Ns) of 5, 10, and 15 dB. Thirty subjects with mild-to-moderate sensorineural hearing losses were tested in quiet and in noise at S/Ns of 10 dB and 15 dB. Monosyllabic words in a Multitalker Noise were selected for testing. Mean scores for the normal-hearing subjects were 45% at the 5 dB S/N, 74% at the 10 dB S/N, and 87% at the 15 dB S/N. For the hearing-impaired subjects, scores were 85% in quiet, 60% at the 15 dB S/N, and 40% at the 10 dB S/N. These results suggest that background noise which is mildly disruptive for normal hearing subjects can be highly disruptive to hearing-impaired subjects. Moreover, these findings indicate that subjects with mild-to-moderate sensorineural hearing loss require a more favourable S/N than normal listeners to achieve comparable word recognition scores. Test-retest differences for word recognition scores revealed variability that agreed closely with predictions based on the binomial distribution for both groups of subjects. Speech-in-noise abilities must be measured directly because regression equations revealed that speech-in-noise scores cannot be predicted accurately from either puretone thresholds or speech-in-quiet scores. Word recognition functions are presented from several hearing-impaired subjects and demonstrate the value of testing in noise.

Acquired Deafness: A Multi-Dimensional Experience

Abstract: The aim of this study was to investigate the subjective experience of acquired deafness using quantitative (questionnaire) and qualitative (interview) methods. This paper presents findings from the questionnaire data. Eighty-seven people (of whom 38 had acquired a profound loss) participated in the study. The questionnaire contained items designed to examine both audiological and non-audiological aspects of deafened people's experiences. It also sought to measure the extent to which those aspects affect their quality of life. The questionnaire included three variables (i.e. reported frequency and impact of depression, and overall effect of deafness on one's life) as broad indicators of adjustment. Seventy-three respondents (including all but one of the profound group) completed the questionnaire. Factor analysis of the questionnaire data identified six major themes (with variance > 10%) underlying the personal experience of acquired deafness. Three themes — communicative deprivation, restriction, ...

Managing Tinnitus: A Comparison of Different Approaches to Tinnitus Management Training

Abstract: A series of studies examining the interaction between the characteristics of individual tinnitus sufferers and the effectiveness of the methods used to assist them has been conducted. The first of these studies provided a baseline description of 96 people with tinnitus, according to a range of audiological and psychological variables. In the present paper four differing tinnitus management programmes are described and the related changes in tinnitus perception reported three months after tinnitus management training. For the majority of subjects, the tinnitus was less annoying and less distressing three months after attending tinnitus management training. However, the majority of subjects reported no change in tinnitus loudness, or tinnitus awareness and no change in their tinnitus coping ability. Subjects receiving low level white noise stimulation reported greater improvement in tinnitus coping ability than subjects who received information and relaxation training, although there was no associat...

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

Abstract: 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.

A review of management of benign paroxysmal positional vertigo by exercise therapy and by repositioning manoeuvres

Abstract: Benign paroxysmal positional vertigo (BPPV) is a common condition that often resolves spontaneously, but can cause significant distress to a patient. Management of this condition includes no intervention, medication, surgery, physical exercises and more recently ‘particle repositioning’ manoeuvres. Repositioning manoeuvres aim to relocate free-floating particles from the posterior semicircular canal into the utricle where they will no longer cause vertiginous symptoms. This article describes the different exercises and repositioning manoeuvres in use and examines their efficacy. In the light of this review a management strategy for BPPV is suggested.

Real-ear to coupler differences in children with grommets.

Abstract: Real-ear to coupler differences (RECDs) are important for the selection of appropriate amplification characteristics for hearing impaired children. The aim of this study was to investigate the effects of patent grommets on RECDs in children. Subjects were 32 children aged between 4 and 7 years, 16 had a patent grommet in one or both ears as confirmed by otoscopy and large equivalent ear canal volumes on tympanometry. There was no evidence of middle ear pathology in the remaining 16 who comprised the control group. All real-ear and coupler measures showed good test-retest repeatability across the whole frequency range. The mean difference in RECDs between the two groups in the frequency range 0.125-0.75 kHz was 15 dB. The differences in RECDs were statistically significant (P < 0.01) for all frequencies below 0.75 kHz. There was a strong correlation between the mean RECD and equivalent ear canal volume at all frequencies between 0.125 and 0.5 kHz, and a moderate correlation at 0.75 kHz. Large inter-subject variability was found, with a maximum standard deviation of 6.6 dB at 4.0 kHz. Therefore, this study supports the need for individual RECD measures to be made, particularly for subjects with grommets, rather than using averaged transformation figures. It suggests that more low frequency gain should be given to hearing aid users with patent grommets to overcome the reduced SPL in the ear canal, due to leakage through the vented tympanic membrane.

The Effect of Head Size on the Auditory Brainstem Response for Two Breeds of Dog

Abstract: Many studies have shown that the auditory brainstem response (ABR) is influenced by the sex of the subject. The explanation offered most often for this sex difference is the smaller head size and brain dimensions in the female. Since breeds of dog have different head sizes, this makes them useful subjects to test the hypothesis that ABR latency covaries with head size. Subjects comprised 20 Dalmatians and 20 Jack Russell terriers. The maximum width of the head was 123 +/- 8 mm in the Dalmatian and 88 +/- 5 mm in the Jack Russell. An auditory brainstem response was carried out using a click stimulus at 75 dB nHL. The latency of wave V and the I-V interval was longer (0.3 and 0.17 ms respectively) in the Dalmatian, although the correlation of these measurements with head size (which ranged from -0.2 to +0.3) was not statistically significant. These findings do not support the theory that differences in ABR latency are due to differences in head size per se. Correlation of latency with body temperature and with age was also weak and not statistically significant.

Changing Performance of the Health Visitor Distraction Test When Targeted Neonatal Screening is Introduced into a Health District

Abstract: The change in the performance of the HVDT as targeted neonatal hearing screening has been introduced has been examined for the Nottingham district. The records for all children born in the period 1984-1993 within the district and having a permanent hearing loss of > or = 50 dB in the better ear have been examined. The referral route leading to ascertainment of the hearing loss as well as the result of any screening tests were noted. The data shows an increase in the number referred prior to the HVDT, mainly as a result of neonatal screen failure. At the same time there has been a reduction in the sensitivity of the HVDT from 78% in the first half of the decade to 38% for the second half. There are also some indications of an increase in the coverage and the failure rate over the time. Possible reasons for these changes are discussed.

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

Abstract: 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

The effects of involvement of the general practitioner and guidance of the hearing impaired on hearing-aid use.

Abstract: A number of international and national publications report that hearing aids are sometimes under used. In this paper, results are reported of a project to increase the effective use of hearing aids. The first intervention was aimed at a more effective exchange of information between the general practitioner (GP) and the ENT specialist. This was achieved by the introduction of a structured referral form. In addition, a simple hearing aid was placed at the GP's disposal for demonstration purposes. As a second, independent intervention, 50% of the patients were visited at home by a trained volunteer. A measure of effective use that combines the effectiveness and actual use had been developed. After the first intervention the non-effective use of hearing aids decreased from 38% to 30%, this being just below statistical significance (p = 0.12). The protocol approach by the GP in combination with the demonstration hearing aid proved to be especially useful. Patients with a counselling visit at home had ...

Measuring the ability of hearing impaired children to understand connected discourse: A comparison of two methods

Abstract: Attempts to quantify the understanding of connected discourse have been based on: the number of embedded key words repeated correctly; the intelligibility ratings estimated by a listener; and the number of content-related questions answered correctly. This study was undertaken to compare the use of the latter two methods to measure the ability of hearing impaired children to understand connected discourse. Twenty-five normally hearing and 54 sensorineural hearing impaired Cantonese-speaking children rated how well they could understand a connected discourse passage, and answered content-related questions to show their level of understanding of the same passage. The effect of two different hearing aid frequency responses and two noise conditions on self-ratings and speech scores was also investigated. Both methods of assessment were able to demonstrate effects of hearing loss, frequency response and noise at approximately similar levels of significance. One of the findings from this study was the absence of any effect of testing method on the performance of the listeners to understand connected discourse. Consequently, either method can be used to provide essential information on the level of difficulty a hearing impaired child might experience in understanding connected speech in everyday life.

Maximum Length Sequences and Volterra Series in the Analysis of Transient Evoked Otoacoustic Emissions

Abstract: Previous work from this group (IHR, Southampton) has shown the feasibility of using maximum length sequence (MLS) stimulation to obtain evoked otoacoustic emissions (OAE). Because an MLS is one of a set of inputs that enables the Volterra series to be computed, we investigated its use with OAE. We wanted to see if the Volterra series could model the system and if we could extract the higher order kernels. In order to realise a practicable MLS system, a variant of the MLS has been used which permits real time recovery of the response and so enables the rejection of noisy epochs. This paper shows that the MLS used does enable the higher order kernels to be measured. The problems of selecting the correct sequences are discussed and the necessary system checks described.

Integrity testing of cochlear implants in the awake child

Abstract: Cochlear implantation is becoming a routine rehabilitation process for profoundly deaf adults and children Often children are implanted at just two or three years of age and therefore the subsequent tuning of the device is challenging Although some children demonstrate quick and reliable responses to electrical stimulation, there are others who do not respond consistently thus causing concern about the functioning of the device It is therefore desirable to have an objective test of the integrity of the implanted electrodes The principle of the integrity test is the measurement of voltages generated by the biphasic current pulses at the electrode array; this is accomplished using surface electrodes placed around the implanted ear, in conjunction with recording and averaging equipment typically used for evoked response testing Traditional integrity testing usually requires a general anaesthetic in young children, however this study demonstrated a simple, quick and reliable method of obtaining results in the normally active child using ear-clip electrodes Results are presented from 12 children tested in this way, and compared with results from 20 children who were tested in theatre using a different electrode configuration The tests were performed in common ground stimulation mode, but some measurements were also made in bipolar + 1 and pseudo-monopolar modes The three stimulation modes were compared, with the conclusion that common ground mode provides an efficient check of implant function in the awake child, while pseudo-monopolar mode may be preferable for anaesthetized patients In addition, measurements were made in vitro using a functioning cochlear implant in a saline tank in order to investigate the current flow during stimulation The standard procedure in this department is to perform a full intra-operative integrity test on all implanted children The simplified technique is used to repeat the measurement post-operatively if required

Self-rated hearing disability in candidates for cochlear implants.

Abstract: A previous scheme for quantification of hearing disability based on self-rating required extrapolation towards the upper end of the range due to lack of data from severely and profoundly impaired subjects. Suitable data have become available more recently from the UK programme evaluating cochlear implantation, thereby providing self-ratings by 465 people with 1-2-3-kHz average hearing threshold levels of 95 dB or greater. The ratings obtained fit the previous extrapolation extremely well. The scheme, therefore, can be applied with confidence to people throughout the range of hearing impairment.

Wiener kernel analysis of a noise-evoked otoacoustic emission

Abstract: In one specimen of the frog species, Rana esculenta, the following were measured: (1) a spontaneous otoacoustic emission; (2) a click-evoked otoacoustic emissions; and (3) a noise evoked otoacoustic emission. From the noise evoked emission response, a first- and a second-order Wiener kernel and the first six polynomial correlation functions were calculated by cross-correlating the stimulus and response signals. A peak near 850 Hz was visible in the spontaneous otoacoustic emission, the click-evoked emission and the noise-evoked emission. The higher order cross-correlation functions did not display any indication of the emission response. Apparently, that the noise stimulus linearizes the evoked emission from the frog's ear.

Audiometer calibration: two neglected areas.

Abstract: British and International Standards for pure tone audiometry require that the static force exerted by the earphone/bone vibrator headband is within certain limits. However, no recommended procedure is given for making force measurements. In addition, standards for audiometers require that linearity of output level is within certain limits. Only a brief outline of a procedure is available for measuring linearity at low intensity levels. Both these areas of audiometer calibration tend to be neglected according to our survey of organizations offering calibration services. Equipment and protocols for measuring both have been developed at the MRC Institute of Hearing Research, and are described. A convenience sample of audiometers gave a wide range of headband forces, many of which do not comply with the relevant standard. Linearity of output at low levels did comply with the relevant standard for all audiometers measured. We recommend the use of simple devices, such as those described, for routine cal...

Time-frequency distribution of evoked otoacoustic emissions

Abstract: Otoacoustic emissions (OAE) are non-stationary signals that vary in time depending on the characteristics of the stimulus. Traditional spectral analysis using Fourier methods ignores the effects of time and can miss important temporal information. Therefore, a better form of spectral analysis requires the use of time-frequency distribution methods. Traditionally, short time Fourier transforms (STFT), commonly known as spectrograms, are used to provide such time-frequency representations. STFT however, suffer from poor resolution and do not provide enough detail about the characteristics of the emissions. In this study, recently developed time-frequency distributions, the Wigner Distribution (WD) and the Choi-Williams Distribution (CWD) are investigated to provide high resolution representations of transient evoked OAEs. Although WD has excellent properties for time-frequency analysis, it suffers from cross-term artefacts generated when multiple sinusoids are present. CWD provides a solution to thi...

A Compact Disc Containing Simulations of Hearing Impairment

Abstract: The author has produced a compact disc (CD) which contains a series of simulations of the effects of cochlear hearing loss The following aspects are simulated: threshold elevation combined with loudness recruitment; reduced frequency selectivity; and threshold elevation, loudness recruitment and reduced frequency selectivity all together The effects are demonstrated using speech in quiet and in a background of noise, and using a piece of music with a wide dynamic range The CD also includes simulations of the effect of having a conventional ‘linear’ hearing aid, and of having a hearing aid incorporating dual-channel fast acting compression Finally, the CD contains demonstrations of the ‘occlusion effect’ and the benefits of having a deeply fitting earmould or hearing aid The purpose of this note is to describe some of the uses of the CD for teaching and educational purposes and to indicate which tracks will be most effective for specific purposes