This report presents a review of the situation in a number of countries with respect to public health policy for funding of hearing aid services in general and support to bilateral fittings in particular. The data show considerable variations among the countries studied in number of hearing aids fitted per 1000 inhabitants, differing by a factor of 6 between the extremes. Also the percentage of bilateral fittings differs with an average estimated to be of the order of 50%. For hearing-impaired children, bilateral fittings are given full financial support in most countries studied. The data presented indicate the need for a reliable, scientifically valid evidence-base regarding bilateral hearing aid fitting. © 2006 British Society of Audiology, International Society of Audiology, and Nordic Audiological Society.

Objective: This paper intends to discuss issues related to cultural, ethnic, and other nonaudiological variables that may affect the response when trying to determine outcome of audiological rehabilitation in different countries. Design: The ideal measure for the determination of outcome of audiological rehabilitation would be sensitive to changes in disability as well as handicap. Further, it would allow unforeseen effects to be identified and not be limited by language borders or cultural and ethnic differences. A variety of critical factors are discussed that are related to culture, social traditions, ethnic factors, etc. that may affect outcome measures and thus make international equivalence difficult. Conclusions: With careful consideration of the factors discussed, a basic set of questions could be formulated and agreed on, calibrated on suitable populations in different countries, and thereafter used as a bridge across borders to allow comparison of different procedures or meta-analyses of studies performed by different laboratories.

Assessment of outcome of hearing aid fitting in children should contain several dimensions: audibility, speech recognition, subjective benefit and speech production. Audibility may be: determined by means of aided hearing thresholds or real-ear measurements. For determining speech recognition, methods different from those used for adult patients must be used, especially for children with congenital hearing loss. In these children the development of the spoken language and vocabulary has to be considered, especially when testing speech recognition but also with regard to speech production. Subjective assessment of benefit to a large extent has to rely on the assessment by parents and teachers for children younger than school age. However, several studies have shown that children from the age of around 7 years can usually produce reliable responses in this respect. Speech production has to be assessed in terms of intelligibility by others, who may or may not be used to the individual child's speech. Ideally, the outcome should be assessed repeatedly at suitable intervals in order to be able to follow the child's communicative development.

   Noise is an increasing problem in everyday life, and many noise-induced hearing problems are irreversible. This book focuses on all aspects of noise-related problems, including noise effects on stress levels, functional changes after noise-induced cochlear damage, occupational hearing loss and noise conservation problems.

Hearing loss gives rise to a number of disabilities. Problems in recognizing speech, especially in difficult environments, give rise to the largest number of complaints. Other kinds of disabilities may concern the reduced ability to detect, identify and localize sounds quickly and reliably. Such sounds may be warning or alarm signals, as well as music and birds singing. The communicative disability affects both hearing-impaired people and other people in their environment-family members, fellow workers, etc. Hearing-impaired people are not always aware of all the consequences of the impairment, they do not always know what they are missing. Several studies have shown that uncorrected hearing loss gives rise to poorer quality of life, related to isolation, reduced social activity, and a feeling of being excluded, leading to an increased prevalence of symptoms of depression. These findings indicate the importance of early identification of hearing loss and offers of rehabilitative support, where the fitting of hearing aids is usually an important component. Several studies also point to a significant correlation between hearing loss and loss of cognitive functions. Most of these studies show such a correlation without being able to show whether the hearing loss caused the reduction in cognitive performance or if both the hearing loss and the cognitive decline are parts of a common, general age-related degeneration. A couple of these studies, however, indicate that the uncorrected hearing loss may be the cause of cognitive decline. Whichever alternative is true, the correlation should be seen as a clear indication for early hearing aid fitting for those needing it. Monaural hearing aid fitting in subjects with bilateral hearing loss may give rise to a reduced ability to recognize speech presented to the unaided ear, the so-called late-onset auditory deprivation effect. This functional decline is reversible in some but not all subjects after fitting of a hearing aid also on the previously unaided ear.

A clinical trial of Oticon DigiFocus hearing aid was performed. The test aid was evaluated on 33 subjects with several years' experience as users of modern analog hearing aids. These aids were used as reference for the 1-month-long trial. The Abbreviated Profile of Hearing Aid Benefit (APHAB) showed a mean difference in benefit with superior ratings for the test aid concerning ease of communication, speech in reverberation and speech in background noise. The subjects' own aids were rated somewhat better concerning aversiveness of sounds, but this difference was not statistically significant. The Gothenburg Profile showed a statistically significant difference between the test aid and the reference aids in favour of the test aid. The difference was not most evident with regard to speech communication and the effects of hearing loss on social interactions. Sound quality ratings concerning clearness were significantly higher for the test aid. Speech recognition thresholds in noise were on average 0.7 dB better for the test aids when tested at speech levels 60 and 75 dB. The difference was statistically significant only at 75 dB. There was significant interaction between general preference and hearing aid type, indicating that overall sound quality was an important factor affecting the general preference for either the test aid or the reference aid. Twenty-three subjects generally preferred the test aid, six preferred their own aid and four stated no difference.

Clinical experience indicates that first-time hearing aid users prefer less gain and lower maximum output levels than experienced users. This hypothesis was tested on 20 subjects being fitted with their first aids. The study was double blinded by using a programmable hearing aid, set to either the standard setting according to the manufacturer's software or to reduced gain and maximum output. Half of the subjects started with one hearing aid and half with the other, changing to the other hearing aid after 3 days trial with each setting. At the end of the study, subjects stated preference in specified situations and overall. No significant differences in APHAB, sound quality, estimated communication ability or perceived loudness scores were seen for the two settings. Nine subjects preferred the standard setting, seven the reduced setting and four were undecided. No correlation could be found between preference and audiological variables.

Clinical procedures related to patients with Alzheimer's Disease (AD) largely fail to address the patient's hearing. Given the challenges of this population, unconventional indicators of treatment efficacy may be required. Palmer et al (1999) reported on caregiver-tracked behaviors as outcome measures for hearing aid intervention. Using these data, hearing aid use and subsequent behavior was modeled as a first-order dynamic system, characterized by responses following an exponential time course. The results of such modeling suggest predictable outcomes of hearing aid intervention, or at least useful parameters of quantification (e.g. time-constant and steady-state response), permitting critical assessment of effects of intervention on negative behaviors versus hearing aid use, comparisons among behaviors, and/or comparisons of hearing-aid-use patterns and behavior counts among patients. Use in this and other difficult-to-test populations warrant further study to evaluate clinical efficacy of the analysis described. © 2005 British Society of Audiology, International Society of Audiology, and Nordic Audiological Society.

The development of integrated circuits during the last decades has made it possible to incorporate digital signal processing in hearing aids that fit into the ear canal and are powered by small zink-air batteries. The digital signal processing provides new possibilities for the hearing aid to modify the signal to fit the impaired ear. A linear phase filter bank that is intended as a basic building block of the signal processing in digital hearing aids is introduced in this dissertation. The filterbank is computationally very efficient and divides the input signal into a number of narrow band signals for further signal processing. The filter bank was combined with band specific gains and two compressors to form the signal processing of a hearing aid. The compressors allow leveldependent gain. Three alternative fitting strategies used to adjust the characteristics of this hearing aid to the individual hearing impaired listener were evaluated. The three fitting strategies differed mainly in the characteristics of the compressors. The strategies were evaluated by hearing impaired subjects in a field test and in laboratory tests. When the subjects were grouped according to their preference among the fitting strategies, the results showed significant differences in the hearing loss configuration between the groups.

One of the main tasks of a hearing aid is to amplify the signal to make it audible for the hearing impaired user. The maximum gain that can be used in a hearing aid will be controlled by the feedback from the output to the microphone, as the hearing aid will be a part of a closed loop system. The feedback path depends on several factors such as the position of the microphone (differs between hearing aid categories), size of vent, and the acoustics around the hearing aid. The feedback, and thus the maximum gain that can be used in a hearing aid, has been identified with a number of different hearing aids in a number of conditions that can be expected when the hearing aid is used under real-life conditions.

Feedback cancellation can be used to reduce the negative effects of feedback on the performance of the hearing aid. An internal feedback in the hearing aid that is an estimate of the external feedback is then used to cancel the feedback signal. The external feedback path will vary as the hearing aid is used ( e.g. when a telephone set is placed by the ear). It is thus desirable to continuously identify the feedback path. One approach to do this is to utilize closed loop identification with the direct method and some recursive identification method. The output and input signals of the hearing aid are then considered as input and output signal of the system to be identified, i.e. the feedback path. An advantage with this method is that the identification can be done without modifying the output signal. A drawback is that the estimate may be biased, depending on the characteristics of the input signal. A difference from many other closed loop identification problems is that the data used for identification will depend on previous estimates of the system. A feedback cancellation algorithm where Filtered-X LMS is used with the direct method has been analyzed. Filtered-XLMS is computationally efficient and gives a possibility to incorporate known characteristics of the feedback path in the model set used. Prefiltering was also used in the algorithm as it can provide an unbiased estimate if the spectrum of the input signal is known.

Experiments in cats have shown that sneezing can be induced using low intensity electrical current. This study focusses on answering the question whether the sneezing-reflex can also be induced in man through electrical stimulation, whether it is reproducible, and if the response can be abolished pharmacologically? Three healthy males were tested using intranasal stimulation in different parts of the nose using a current from an electric pulse generator. Using currents in the range 2-11 mA, it was possible to induce and reproduce sneezing in the anterior portion of the nose corresponding to the distribution area of the anterior ethmoidal nerve. In one tested subject, local anaesthetics applied to the mucous membranes of the nose abolished the sneezing. Sneeze reflex-reduction may be one way to reduce viral contamination between subjects. Further research could include pharmacological investigations to identify a sneeze-inhibiting substance with small risks for side effects that can be added to common cold nasal sprays.

Central auditory processing is complex and can not be completely evaluated by a single method. This thesis focuses on assessment of some aspects of central auditory functions by the use of dichotic speech tests, cognitive tests that tax functions important for speech processing and electrophysiological tests.

Paper A deals with the cognitive effects in dichotic speech testing in elderly hearing impaired subjects. Dichotic speech tests and cognitive tests were performed on 30 hearing impaired subjects ranging in age from 42 to 84 years. The dichotic test material consisted of digits, short sentences and consonant-vowel-syllables. The cognitive test material comprised tests for short-term memory, verbal information processing and phonological processing. Effects of age in dichotic speech tests in elderly were verified. The degree of effect was dependent upon focusing condition and test material. The different listening tasks in the dichotic tests put different demands on cognitive ability, shown by a varying degree of correlation between cognitive functions and dichotic test parameters. Age-related cognitive decline in the elderly was strongly connected with problems to perceive stimuli presented to the left ear.

Paper B presents a new cognitive test battery, performed in text, auditory and audiovisual modalities. The tests are sensitive for functions important for speech processing and understanding. The test battery was evaluated in four groups, differing in age and hearing status. Each group comprised twelve subjects. The effect of low-level noise on cognitive functions was investigated. The only significant result in the text modality was an age effect in speed of performance, which was also seen in the auditory and audiovisual modalities. In the auditory and audiovisual modalities effects of hearing status and modality were seen in accuracy parameters. Interaction between hearing status and modality, both in accuracy and speed of performance, shows that hearing-impaired subjects benefit more from visual cues. In noise generally poorer results were obtained, especially in the auditory modality and for the elderly, affecting both accuracy and speed. The test battery has proven to be useful in assessing the relative contribution of different input-modalities and the effect of age, hearing-impairment and visual contribution on functions important for speech processing.

Paper C describes the development of a system for recording of auditory evoked potentials. The system is built around a personal computer with a data-acquisition board with analogue input and output channels. Acoustic stimuli are presented to the test subject and responses to the acoustic stimuli are recorded in an EEG-recording system. The program is written in the graphical programming environment LabView (National Instruments). With the system it is possible to perform all clinical standard measurements. In addition, test-procedures not available in commercial auditory evoked potential systems have been developed. For the assessment of auditory discrimination a toolkit for evaluation of the mismatch negativity potential was developed and evaluated in six normal-hearing subjects.

A Swedish Hearing In Noise Test (HINT), consisting of everyday sentences to be used in an adaptive procedure to estimate the speech recognition thresholds in noise and quiet, has been developed. The material consists of 250 sentences, with a length of five to nine syllables, normalized for naturalness, difficulty and reliability. The sentences were recorded with a female speaker. From the sentences, 25 phonemically balanced lists were created. All lists fluctuate less than 1 dB of the overall mean. The standard deviation of the test-retest difference is 0.94 dB when testing with one list, and decreases to 0.68 dB and 0.56 dB for two and three lists, respectively. The average speech recognition thresholds in noise for the Swedish sentences were -3.0 dB signal/noise ratio (SD = 1.1 dB). The present study has resulted in a well-defined and internationally comparable set of sentences, which can be used in Swedish audiological rehabilitation and research to measure speech recognition in noise and quiet. © 2006 British Society of Audiology, International Society of Audiology, and Nordic Audiological Society.

Speech recognition and cognitive functions important for speech understanding were evaluated by objective measures and by scores of perceived effort, with and without hearing aids. The tests were performed in silence, and with background conditions of speech spectrum random noise and ordinary speech. One young and one elderly group of twelve hearing-impaired subjects each participated. Hearing aid use improved speech recognition in silence (7 dB) and in the condition with speech as background (2.5 dB S/N), but did not change the perceived effort scores. In the cognitive tests no hearing aid benefit was seen in objective measures, while there was an effect of hearing aid use in scores of perceived effort, subjects reported less effort. There were no age effects on hearing aid benefit. In conclusion, hearing aid use may result in reduced effort in listening tasks that is not associated with improvement in objective scores. © 2005 British Society of Audiology, International Society of Audiology, and Nordic Audiological Society.

Jacoby's white noise task and an explicit recognition task were used to investigate whether individuals with eating disorders demonstrate implicit memory bias and explicit memory bias, respectively, for information related to eating and body appearance. Included were 33 women with eating disorders (seven with anorexia nervosa and 26 with bulimia nervosa), 29 with nonclinical eating disorder‐related concerns, and 36 healthy controls. Results showed partial support for implicit memory bias but no support for explicit memory bias. These findings suggest that eating disorders may be characterized by relative initial automatic bias for eating disorder‐relevant information but not by bias at later stages of information processing. However, previous studies have demonstrated explicit memory bias in eating disorders, which is inconsistent with this interpretation. Future research is required to clarify the precise cognitive biases associated with eating disorders.

Relevant reference data are required in order to determine the effect from occupational noise exposure on hearing. Pure-tone averages (PTA) of hearing threshold levels simplify the evaluation for audiometric frequencies typically affected by noise. The present study provides reference data of high frequency (HF) PTA over 3, 4 and 6 kHz for a general adult population, aged from 20 to 79 years, not exposed to hazardous occupational noise. The results are presented as statistical distributions of HF PTA values as functions of age, and as prevalence of different degree of HF PTA in the age groups 20-29, 30-39, 40-49, 50-59, 60-69 and 70-79 years.

A method for evaluating the spectral, temporal and combined spectral temporal resolution of hearing is presented; it was used to obtain masked hearing thresholds using the fixed frequency Békéy technique. The masking noise was a broadband random noise with a 3 dB/octave roll off (pink noise). Spectral resolution was assessed by introducing a spectral gap in the masking noise centered at the test tone frequency. Temporal resolution was assessed by introducing temporal gaps, the centre of which coincided in time with the centre of the test tone-pulses. The spectral and temporal gaps were used either separately or simultaneously. Release of masking values were calculated from masked hearing thresholds. One test group comprised 16 normal-hearing subjects, a second group 16 elderly (age 55-75 years) subjects with normal hearing for their age. Temporal gaps were 20, 50 and 100 ms long. Spectral gaps had a bandwidth of 1/10, 1/3, and 1 octave. Each gap or combination of gaps was tested at the frequencies 0.5, 1, 2 and 4 kHz. Release of masking increased with increasing temporal or spectral gaps. If a temporal gap and a spectral gap were combined, the release of masking increased further. Maximum release of masking was obtained with the 100 ms temporal gap combined with the 1 octave notch filter. The overall difference in release of masking between the young and elderly normal-hearing group was 2 dB.

A system for recording of evoked potentials from auditory stimulation was developed. The system consists of a PC equipped with an audio bandwidth board with analog input and output channels. The sound stimulus signal is generated in the computer, D/A converted, and via audio amplifier fed to earphones on the test subject. Auditory evoked potentials in response to sound stimuli are recorded via electrodes, amplified and filtered in an EEG recording system and fed to an A/D converter. The signal is analysed in the PC. The modular design of the program makes it a flexible system where stimulus and recording parameters can easily be modified and new applications can be added to standard clinical measurements.

Three applications that are not possible with commercially available systems were developed and evaluated. a) A diagnostic procedure to verify hydrops in patients with Meniere's disease. b) Intraoperative recordings of auditory evoked potentials during neurootological surgery. c) Recording of mismatch negativity (MMN) potentials in evaluation of central auditory functions.