The increasing degree of sophistication in hearing aid technology calls for appropriate fitting strategies, as otherwise hearing aid users cannot receive the full benefit from the most modern technological achievements. This paper describes the state of the art in hearing aid fitting procedures and offers a look into possible future developments. Currently, threshold-based fitting formula compete with loudness- and sound-based fitting procedures. Whereas threshold-based approaches are straightforward and timesaving, they do not consider loudness growth and the sound preferences of the listener. On the other hand, loudness- and sound-based procedures do take these aspects into account, but they are time consuming and it is not yet proven that they provide higher benefit for the end user. This may be due to the fact that either there is actually no extra benefit or more likely that the evaluation tools or study designs have to be improved. Concerns about how to fit more advanced future hearing instruments seem to be inappropriate, as an analysis of possible future signal processing algorithms shows that they probably do not need extra fitting to the individual hearing impairment but rather need optimization according to the acoustical environment.
Calculations of the needs of healthcare, hearing healthcare included, are usually based on clinical data rather than on valid prevalence figures. According to our recent population study, the number of citizens needing hearing aids in Finland will be twice the figure usually presented, 280 000 for the country as a whole (population 5.1 million). The penetration of hearing aids was only 41%. Taking this and the ageing of the population into account, the economic challenges of hearing healthcare will be alarming in the new millennium.
The majority of hearing impaired children live in the developing countries. Limited resources are available for screening, prevention, diagnosis and intervention. These problems were the topic for discussion in a special session in the Congress.
Brainstem auditory-evoked potential (BAEP) examinations were performed in 15 patients with long-standing type-1 diabetes mellitus (DM). Cardiovascular reflex tests were applied for assessment of autonomic neuropathy. The aim of our investigation was to compare the BAEP results of this patient group with controls and to look for a possible correlation between the alteration of the auditory brainstem function and the cardiovascular autonomic neuropathy. Analysis of the latencies (waves I, II, III and V) and the inter-peak latencies (waves I-III and I-V) of BAEPs revealed a significant difference between diabetics and healthy controls. The amplitudes of waves I, III and V were definitely lower in comparison with those of healthy controls. A positive correlation was observed between the overall autonomic score and the latencies (waves III and V) and inter-peak latencies (waves I-III and I-V). These data support the hypothesis that long-standing DM and diabetic neuropathy might be related as a cause of certain dysfunctions of the central auditory pathways.
The role of medial efferent system in regulating outer hair cell function has been studied by many investigators. Usually narrow band noise or white noise as contralateral stimulation (CS) suppressors have been used and changes in OAE amplitudes estimated. Thirty children aged 6-15 years (mean 12.5 ± 4.7), without any changes in tonal and impedance audiometry and with negative history regarding otiatric diseases were examined. Transient evoked otoacoustic emissions (TEOAE) were recorded using ILO 92 Otodynamics Analyser. CS was performed using 1.0 kHz and 2.0 kHz continuous pure tones of 30 dB SL or 50 dB SL. Effects of CS on TEOAE evoked by click of 80, 70 and 60 dB SPL were investigated. TEOAE analysis included assessment of TEOAE amplitude of half octave frequency bandwidth (HOFBW-1.0; HOFBW-1.5; HOFBW-2.0; HOFBW-3.0 and HOFBW-4.0 kHz) and 0.8 kHz frequency bandwidth (0.8-FBW) amplitudes centred at 1.0; 2.0; 3.0; 4.0 and 5.0 kHz. TEOAE amplitude recorded for stimuli 80, 70 and 60 dB SPL without CS decreased: mean values respectively 6.1 ± 4.2; 5.4 ± 4.5 and 3.3 dB SPL ± 4.3. CS effect on TEOAE was observed for all CS options, however, larger suppressive effect was recorded on TEOAE elicited by 70 dB SPL stimulus using 1 kHz/50 dB SL tone as a suppressor and on TEOAE elicited by 60 dB SPL stimulus using 2 kHz/50 dB SL tone as a suppressor. HOFBW and 0.8-FBW analyses showed the association between the frequency/intensity of the suppressors and decreasing of amplitudes of adequate frequency bands. It is concluded that the described method of investigating of the medial olivocochlear efferent system seems to be sensitive and confirms frequency-dependent suppressive effect on OAE.
When stimulated with an appropriate stimulus, the hair cells of the organ of Corti depolarize, causing the release of a neurotransmitter substance, which excites afferent VIIIth nerve dendrites. It is reasonable to hypothesize that excitatory postsynaptic potentials (EPSPs) generated by the dendrites of the auditory nerve in turn initiate a compound action potential (CAP). The EPSP is thought to be the generator potential for the CAP, and may be recorded in auditory brainstem responses (ABRs) as the I ' potential. Determining the anatomical origin of I ' may enhance the sensitivity of the ABR technique in hair cell/dendrite/auditory nerve evaluations. Whether I ' is of sensory or of neural origin is equivocal, and therefore I ' is not well understood. To investigate this dilemma, ABRs were recorded from human subjects using standard and paired-click stimuli, and using subtraction methods to generate a derived ABR. Two early peaks, designated as I degrees and I ', occurred before wave I in the derived ABR. It was hypothesized that peaks I degrees and I ' represent the summating potential and the generator potential, generated by the cochlea and VIIIth nerve dendrites, respectively.
About one in five adults has some form of hearing impairment. This paper reports on a survey which found significant variation in the provision of hearing aid services across Denmark, Finland, Norway, Sweden and the United Kingdom. Per capita expenditure levels were estimated to vary from under 3 euros in the UK to nearly 10 in Denmark and Norway. Annual figures for the number of people receiving at least one aid varied from around eight per 1000 in the UK and Denmark to 2.2 in Finland. Over 50% of hearing aid users in Norway and Denmark are estimated to have bilateral aids, compared to under 15% in the UK. Estimates of the number of people who have a hearing aid in these countries are considerably lower than the number who have a hearing impairment. More research is needed to verify the true extent of these differences and their cause.
Universal newborn hearing screening (UNHS) is rapidly becoming 'standard of care' in the United States. More than two dozen states now require, through legislative mandate, that the state establishes a system for early hearing detection and intervention (EDHI), beginning with mandated UNHS. In states with long-standing EDHI programs, the average age of identification and intervention has decreased significantly. In those states, infants are identified and intervention initiated typically before age 6 months, meeting the Joint Committee on Infant Hearing's (JCIH) recommendation for newborn hearing screening, diagnosis and intervention. Language outcome data suggest that earlier intervention results in better language outcomes for deaf and hard-of-hearing children. This article reviews the current status of UNHS in the United States, summarizes the Colorado statewide program and describes the JCIH Year 2000 position statement for developing comprehensive EDHI programs.
Hearing aid fitting strategies for children have largely developed separately from those for adults. There has, however, been little consideration of whether children's amplification requirements are different, except for the physical effects of differences in ear canal size. This paper summarizes the fitting strategies for children, and examines whether children require more (or less) gain for high-, medium- or low-level sounds, or a different frequency response, compared with adults with similar hearing loss. Research relating to the above questions is reviewed. The gain that children require for high-level sounds is not different than for adults because loudness discomfort levels are similar. The gain children prefer for medium-level sounds is the same, or only slightly more, than is preferred by adults. Children may require greater gain for low-level sounds because they do require higher signal levels to achieve the same level of speech understanding as adults do. There are, however, arguments why more gain for low-level sounds may not be desirable. The frequency response children prefer is the same as that preferred by adults. New methods for evaluating individual fittings are briefly discussed.
The patients with tinnitus and/or hyperacusis undergoing an 18-24 month period of TRT are divided into five categories of treatment. Different types of counselling and sound therapy are used in each category. Selection of patients into a specific category depends on such factors as: hyperacusis, subjective hearing loss and long-lasting effect of noise on tinnitus. The 108 cases were evaluated After 1 year of treatment. The results of therapy of 40 patients with tinnitus and subjective hearing loss (category II) were compared with the results of therapy of patients with tinnitus only (categories 0 and I). A special questionnaire, answered before and during the treatment, was used to assess the results. Our data indicate significant improvement in about 70% of patients with tinnitus only and in about 90% of patients with tinnitus and subjective hearing loss after one year of therapy.
In this paper, machine learning methods based on artificial intelligence theory are applied to the computer-aided decision making of some otoneurological diseases, for example Ménière's disease. Three methods explored are decision trees, genetic algorithms and neural networks. By using such a machine learning method, the decision-making program is trained with a representative training set of cases and tested with another set. The machine learning methods are useful also for our otoneurological expert system, One, which is based on a pattern recognition approach. The methods are able to differentiate most of the cases tested between the six diseases included, provided that a sufficiently large training set is available.
In order to find an adequate fitting strategy for digital compression hearing aids a combination of two interactive fitting strategies was developed, one of these based on frequency specifice loudness (ScalAdapt) and the other based on overall loudness and on sound quality (Cambridge Procedure). This new fitting strategy was tested against the sound and overall loudness based strategy and against a prescriptive fitting strategy in a 2-weeks field test with questionnaires and in laboratory measurements, subjectively as well as objectively. With six sensorineural hearing impaired participants no straightforward results were achieved. Additionally, the different testing procedures indicate (in tendency) different fitting strategies to be superior. More subjects will have to be tested and innovative evaluation methods have to be considered.
A battery of Arabic speech material was developed for remediation of selective auditory attention disorder (SAAD) in children and standardized on 40 normal children aged from 6 to 12 years. This battery included: the Word Intelligibility by Picture Identification (WIPI) test, newly developed sentences for speech discrimination in noise, bisyllabic words and monosyllabic words. The tests were recorded against a background noise of either multitalker babble or stories. Variables affecting the results of the new battery, namely age, type of speech material and type of background noise, were studied. A significant positive correlation was found between the age of the child and the test scores. The WIPI test was the easiest test, giving the highest scores. The monosyllabic words test was the most difficult, yet normal children gave mean scores around 92%. The type of background noise showed a non-significant effect on the test scores. Results of two cases with SAAD are also presented.
We have made a retrospective analysis on 70 prelingually deaf children (78% congenital; age range 2-15 years) followed for up to 5 years post-implant during which both closed set speech perception tests (TAC, WIPI) and open set tasks (PBK, GASP) were administered. We used a binary partitioning algorithm to optimally divide our dataset on the basis of age at implantation This technique achieves an optimal split when the heterogeneity of the data is most reduced (maximal drop in deviance). For the closed set speech perception tests (TAC and WIPI) partitioning best divided-out data at age 4.4 years. For the open set tests optimal division was at a higher age of implantation (GASP word, 5.6 years; PBK word, 8.4 years). Using these partitioning values, we have found statistically significant differences between rate of improvement of scores in the younger implanted children compared with those implanted later.
Evidence is presented about the limitation of information available on prevalence/incidence of deafness and hearing impairment in the developing world, particularly in Latin America. Two questionnaires on audiological resources and services were mailed to Latin American and Caribbean countries in general and to Central American nations in particular. The information returned by Argentina, Chile, Colombia, Costa Rica, Cuba, Belize, El Salvador, Grenada, Guatemala, Honduras, Mexico, Nicaragua, Panama, Puerto Rico and Uruguay was analysed. Data was gathered about epidemiological studies on hearing impairment, about specific programmes, such as early identification of hearing impairment, national registers on deafness and programmes on hearing screening. Training programmes and availability of professionals in the field of hearing and deafness is also shown. Hearing services, hearing aids provision, hearing testing equipment, professional organization and legislation in audiology is also documented. It is our conclusion that hearing impairment is a low priority for health systems in the developing world, technology continues to be excessively costly and material and human resources are limited, and services are poor and restricted.
A computerized adaptive Finnish speech in noise test was developed recently. As part of the test's evaluation process 172 patients with sensorineural hearing loss including 20 normally hearing subjects were measured using pure-tone audiometry, speech recognition threshold in noise (SRTN) test and conventional speech audiometry without background noise. As anticipated, sensorineural hearing loss yielded an elevation of SRTN although individual differences were considerable. The SRTN test was accurate as the absolute difference between individual repeated SRTNs was, on average, 1.5 dB (SD 1.5 dB) when the range of possible test values is from approximately -12 to +20 dB. On average, the learning effect was 0.5 dB.
A natural and a synthetic face were compared with regard to speech-reading performance, with a visual and an audio-visual condition, and with three levels of contextual cueing in an experiment with 90 normal-hearing subjects. Auditory presentation (speech in noise) served as a control condition. The results showed main effects for type of face, presentation mode and contextual cueing, and also an interaction between presentation mode and type of face, such that performance was superior for the natural compared with the synthetic face, and especially in the audio-visual mode. Audio-visual speech-reading was more accurate than visual and auditory presentation and contextual cueing improved performance overall. It is suggested that a synthetic face can be a valuable and useful support if proper cueing and an auditory signal are provided, but it is outperformed by a natural face with regard to complementarity to an underspecified auditory speech signal.
In recent years the need for reliable data on permanent childhood hearing impairment (PCHI) has increased, owing to both scientific interest and practical aspects such as implementation of neonatal hearing screening. In order to obtain data about the epidemiology of PCHI in the Austrian state of Tyrol, the medical records of all hearing-impaired Tyrolean children born between 1980 and 1994 were researched. A total of 165 children with at least moderate hearing impairment in the better ear were registered, of whom 52.7% were found to be moderately hearing-impaired, 24.2% severely hearing-impaired and 23.0% profoundly hearing-impaired. Sensorineural hearing loss was observed in 87.3%, conductive hearing loss in 6.7% and mixed hearing loss in 6.1%. As for aetiology, non-syndromic hereditary hearing loss was diagnosed in 22% of the children and syndromic hearing loss in 8%. Congenital malformation of the ear was found in 3%. In 19% of the children, perinatal risk factors were seen, and in 10% a pre-, peri- or postnatal infection had occurred. Aetiology remained unknown in 36% of the children. The prevalence rate of newborn hearing impairment was 1.27/1000 newborns. The results are considered to fit well to the PCHI findings reported from other European regions.
A computerized adaptive Finnish speech-in-noise test has recently been developed. The purpose of the present study was to measure speech recognition thresholds in noise (SRTN) in patients with sensorineural hearing impairment (SNHI) caused by mitochondrial mutation [mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS)] and in patients with SNHI from other causes and to compare them with those in normal hearing controls. SRTN differed significantly between controls and the patients with SNHI from other causes and between controls and the MELAS group, but not between SNHI patients and the MELAS group. Hearing in a noisy environment seems to be as impaired in MELAS patients as in patients with SNHI from other causes, in spite of the possible coexisting defects in the central nervous system.
