Valganciclovir in Infants with Hearing Loss and Clinically Inapparent Congenital Cytomegalovirus Infection: A Nonrandomized Controlled Trial

OBJECTIVE

To assess the efficacy of valganciclovir in infants with hearing loss and clinically inapparent congenital cytomegalovirus infection (cCMV), as there is no consensus on treatment of this group.

STUDY DESIGN

A nationwide, nonrandomized controlled trial, comparing 6 weeks of oral valganciclovir to no treatment in infants with cCMV, recruited after newborn hearing screening resulted in referral to an audiologist. The choice whether to treat was left to parents of subjects. Eligible subjects were full term infants aged <13 weeks with sensorineural hearing loss and diagnosed with cCMV through dried blood spot testing. The primary outcome, measured by linear and ordinal logistic regression, was change in best-ear hearing from baseline to follow-up at 18-22 months of age.

RESULTS

Thirty-seven participants were included in the final analysis, of whom 25 were in the treatment group and 12 in the control group. The majority of subjects in both groups had neuroimaging abnormalities, which were mostly mild. Hearing deterioration was more likely in the control group compared with the treatment group (common OR 0.10, 95% CI 0.02-0.45, P = .003). Mean best-ear hearing deteriorated by 13.7 dB in the control group, compared with improvement of 3.3 dB in the treatment group (difference 17 dB, 95% CI 2.6 - 31.4, P = .02).

CONCLUSIONS

We investigated treatment in children with hearing loss and clinically inapparent cCMV. Although our study was nonrandomized, it is the first prospective and controlled trial in this population. Valganciclovir-treated children with hearing loss and inapparent cCMV had less hearing deterioration at 18 through 22 months of age than control subjects.

EUDRACT REGISTRY NUMBER

2013-003068-30.

Targeted screening for congenital cytomegalovirus infection: clinical, audiological and neuroimaging findings

OBJECTIVE

To evaluate clinical, audiological and neuroimaging findings in a cohort of infants diagnosed with congenital cytomegalovirus (cCMV) infection after failure at newborn hearing screening.

METHODS

A prospective observational study in the Netherlands, using the existing newborn hearing screening infrastructure for well babies. Between July 2012 and November 2016, cytomegalovirus (CMV) PCR testing of neonatally obtained dried blood spots (DBS) was offered to all infants who failed newborn hearing screening. Clinical, neuroimaging and audiological data were collected.

RESULTS

DBS of 1374 infants were successfully tested and 59 were positive for CMV (4.3%). Data of 54 infants were retrieved. Three were small for gestational age and six had microcephaly. Forty-eight (89%) had sensorineural hearing loss (SNHL), of whom half had unilateral SNHL. In both unilaterally and bilaterally affected children, the majority of the impaired ears had severe or profound hearing loss. Neuroimaging abnormalities were found in 40 of 48 (83%) children who had evaluable cranial ultrasound and/or cerebral MRI. The abnormalities were mild in 34, moderate in 3 and severe in 3 infants. The degree of SNHL and the severity of neuroimaging abnormalities were found to be correlated (p=0.002).

CONCLUSIONS

The yield of targeted cCMV screening following newborn hearing screening failure was eight times higher than the estimated national birth prevalence of cCMV. The majority of this cohort of infants with clinically unsuspected cCMV disease had confirmed SNHL, neuroimaging abnormalities and lower than average birth weights and head circumferences. Newborns who fail newborn hearing screening should be tested for CMV to ensure appropriate clinical, neurodevelopmental and audiological follow-up.

The School Career of Children With Hearing Loss in Different Primary Educational Settings-A Large Longitudinal Nationwide Study

Children with hearing loss (HL) are at risk for a lower educational achievement. This longitudinal study compared the school career of a nationwide Dutch cohort with and without HL based on descriptive data of the governmental authority Statistics Netherlands. From 2008 to 2018, 3,367,129 children, of whom 1,193 used cochlear implants (CIs) and 8,874 used hearing aids (HAs), were attending primary and/or secondary education. Sixty-one percent of children with HL attended mainstream and 31% special primary education. Compared to mainstreamed pupils without HL, mainstreamed pupils with HL achieved lower levels for language and mathematics in primary education but eventually attended comparable types of secondary education. Children with HL attending special primary education attained lower types of secondary education compared to mainstreamed peers with and without HL. These findings suggest that future educational (and as a result professional) attainment of a child with HL depends on the type of primary educational setting.

Quality of life of children with hearing loss in special and mainstream education: A longitudinal study

OBJECTIVES

To compare the quality of life (QoL) of children with hearing loss (HL) and children with normal hearing (NH) and to examine how the QoL of children with HL changes over time, considering language skills, type of hearing device, degree of HL, and type of education.

METHODS AND MATERIALS

This longitudinal study included 62 children with HL and their parents. Developmental outcome data were collected at two time points, when the mean ages of the children were 4 and 11 years. The Pediatric Quality of Life (PedsQL™) questionnaire, which includes assessments of Physical, Emotional, Social, and School functioning, was completed by parents at both time points and by the children with HL at the second time point. Receptive and expressive language skills at 4 years were assessed by the Reynell Developmental Language Scale. Results were compared with a Dutch normative sample.

RESULTS

The QoL of children with HL was similar to that of children with NH at both time points on two of the four QoL scales, Emotional and Physical functioning. On the other two scales, Social and School functioning, children with HL who attended special education and children who switched to mainstream education showed lower scores than children with HL who were consistently in mainstream education and lower scores than children with NH. The School QoL of children with HL decreased over time, as did the School QoL of children with NH. Social QoL of children with cochlear implants decreased over time, but this was not the case in children with hearing aids. Language skills and the degree of HL did not clinically improve the QoL over time of preschool children with HL.

CONCLUSIONS

The QoL of children with HL in mainstream education and the Physical and Emotional QoL of all children with HL were satisfactory. It is essential to develop specific guidance regarding school activities for children with HL in special education and for children with HL who switch to mainstream education in order to increase their social QoL.

Systematic Evaluation of Self-Reported Hearing Ability in Six Dimensions Before and After a Hearing Aid Trial

Purpose The aim of the study was to evaluate the application of a modified version of the Amsterdam Inventory for Auditory Disabilities and Handicap to inventory self-reported hearing difficulties pre and post hearing aid fitting in 6 dimensions: detection, speech in silence, speech in noise, localization, discrimination, and noise tolerance. Method Questionnaires pre and post hearing aid fitting were collected during regular practice of hearing aid provision. Data of 740 subjects are presented; 337 already used hearing aids, and 403 were new users. Results Group-averaged scores improved due to hearing aid fitting for all 6 dimensions. Based on a criterion previously defined for the Amsterdam Inventory for Auditory Disabilities and Handicap questionnaire, 66% of subjects had a significant individual improvement in sum score. Experienced users showed lower improvement in scores, whereas their aided prescores were, on average, not better than the (unaided) score of 1st users. Conclusions The questionnaire can be applied as a structured approach to inventory hearing problems in 6 dimensions prior to hearing aid fitting and to systematically evaluate the effects of hearing aid fitting after a trial period. The data presented here can serve as normative data for comparison of individual subjects in clinical practice.

Terrible Twos or Early Signs of Psychopathology? Developmental Patterns in Early Identified Preschoolers With Cochlear Implants Compared With Hearing Controls

OBJECTIVE

Cochlear implants (CIs) have dramatically improved the lives of children who are deaf or hard of hearing; however, little is known about its implications for preventing the development of psychiatric symptoms in this at-risk population. This is the first longitudinal study to examine the early manifestation of emotional and behavioral disorders and associated risk and protective factors in early identified preschoolers with CIs compared with hearing peers.

DESIGN

Participants were 74 children with CIs and 190 hearing controls between ages 1 and 5 years (mean age, 3.8 years). Hearing loss was detected using the Newborn Hearing Screening in The Netherlands and Flanders. Parents completed the Early Childhood Inventory-4, a well-validated measure, to evaluate the symptoms of DSM-IV-defined psychiatric disorders, during three consecutive years. Language scores were derived from each child's medical notes.

RESULTS

Children with CIs and hearing controls evidenced comparable levels of disruptive behavior and anxiety/depression (which increased with age in both groups). Greater proficiency in language skills was associated with lower levels of psychopathology. Early CI and longer duration of CI use resulted in better language development. In turn, higher early language skills served as a protective factor against the development of disruptive behavior symptoms.

CONCLUSIONS

This longitudinal study uniquely shows that improvement in language skills mitigates the development of early signs of psychopathology. Early identification of hearing loss and CIs help children improve their language skills.

Evaluation of Auditory Functioning and Rehabilitation Using Patient-Reported Outcome Measures

There is lack of a systematic approach concerning how to select an adequate hearing aid and how to evaluate its efficacy with respect to the personal needs of rehabilitation. The goal of this study was to examine the applicability and added value of two widely used self-reporting questionnaires in relation to the evaluation of hearing aid fitting. We analyzed responses, pre- and postfitting, from 1,319 subjects who completed the Client Oriented Scale of Improvement (COSI) and a slightly adapted version of the Amsterdam Inventory for Auditory Disability and Handicap (in Dutch: AVAB). Most COSI responses were at or near the maximum possible score. Results show a close relation between COSI's degree of change and final ability (Spearman's rho = 0.71). Both AVAB and COSI showed a significant effect of hearing aid experience, but-in contrast to AVAB-COSI did not show a significant effect of the degree of hearing loss. In addition, a Friedman test showed significant differences between six dimensions of auditory functioning for both AVAB and COSI, although post hoc analysis revealed that for COSI, the dimension speech in quiet explained most variation between dimensions. In conclusion, the effects of hearing loss were more salient in AVAB, while both AVAB and COSI showed differences regarding hearing aid experience. Combining the advantages of both methods results in a detailed evaluation of hearing aid rehabilitation. Our results therefore suggest that both methods should be used in a complementary manner, rather than separately.

Benefit of contralateral routing of signals for unilateral cochlear implant users

One way to improve speech understanding in noise for HI with a unilateral hearing loss is by contralateral routing of signals (CROS). Such a CROS-system captures sounds with an additional microphone at the worst hearing ear and transmits these to the better one. The better ear is then provided with a mix of signals originating from both ears. The goal of this study is to quantify the effect of a CROS-system on speech reception thresholds (SRTs) with unilaterally implanted CI-users in diffuse and directional noise as a function of speaker location. Listening tests are performed and an accurate directional intelligibly model is proposed used for further analysis. In diffuse noise it is concluded that the use of a CROS system results in a maximum gain in SRT of 7.9 dB when speech comes from the CROS side compared to a maximum loss in SRT of 2.1 dB when speech comes from the implanted side. In the case of directional noise, the effect of the CROS is symmetric and the maximum loss or gain in SRT was around 9 dB. The study therefore shows a clear potential of using the CROS system in diffuse noise.

Symptoms of Psychopathology in Hearing-Impaired Children

OBJECTIVES

Children with hearing loss are at risk of developing psychopathology, which has detrimental consequences for academic and psychosocial functioning later in life. Yet, the causes of the extensive variability in outcomes are not fully understood. Therefore, the authors wanted to objectify symptoms of psychopathology in children with cochlear implants or hearing aids, and in normally hearing peers, and to identify various risk and protective factors.

DESIGN

The large sample (mean age = 11.8 years) included three subgroups with comparable age, gender, socioeconomic status, and nonverbal intelligence: 57 with cochlear implants, 75 with conventional hearing aids, and 129 children who were normally hearing. Psychopathology was assessed by means of self- and parent-report measures.

RESULTS

Children with cochlear implants showed similar levels of symptoms of psychopathology when compared with their normally hearing peers, but children with hearing aids had significantly higher levels of psychopathological symptoms, while their hearing losses were approximately 43 dB lower than those of children with implants. Type of device was related with internalizing symptoms but not with externalizing symptoms. Furthermore, lower age and sufficient language and communication skills predicted less psychopathological symptoms.

CONCLUSIONS

Children who are deaf or profoundly hearing impaired and have cochlear implants have lower levels of psychopathological symptoms than children with moderate or severe hearing loss who have hearing aids. Most likely, it is not the type of hearing device but rather the intensity of the rehabilitation program that can account for this difference. This outcome has major consequences for the next generation of children with hearing loss because children with profound hearing impairment still have the potential to have levels of psychopathology that are comparable to children who are normally hearing.

Low empathy in deaf and hard of hearing (pre)adolescents compared to normal hearing controls

OBJECTIVE

The purpose of this study was to examine the level of empathy in deaf and hard of hearing (pre)adolescents compared to normal hearing controls and to define the influence of language and various hearing loss characteristics on the development of empathy.

METHODS

The study group (mean age 11.9 years) consisted of 122 deaf and hard of hearing children (52 children with cochlear implants and 70 children with conventional hearing aids) and 162 normal hearing children. The two groups were compared using self-reports, a parent-report and observation tasks to rate the children's level of empathy, their attendance to others' emotions, emotion recognition, and supportive behavior.

RESULTS

Deaf and hard of hearing children reported lower levels of cognitive empathy and prosocial motivation than normal hearing children, regardless of their type of hearing device. The level of emotion recognition was equal in both groups. During observations, deaf and hard of hearing children showed more attention to the emotion evoking events but less supportive behavior compared to their normal hearing peers. Deaf and hard of hearing children attending mainstream education or using oral language show higher levels of cognitive empathy and prosocial motivation than deaf and hard of hearing children who use sign (supported) language or attend special education. However, they are still outperformed by normal hearing children.

CONCLUSIONS

Deaf and hard of hearing children, especially those in special education, show lower levels of empathy than normal hearing children, which can have consequences for initiating and maintaining relationships.

Self-esteem in hearing-impaired children: the influence of communication, education, and audiological characteristics

OBJECTIVE

Sufficient self-esteem is extremely important for psychosocial functioning. It is hypothesized that hearing-impaired (HI) children have lower levels of self-esteem, because, among other things, they frequently experience lower language and communication skills. Therefore, the aim of this study was to compare HI children's self-esteem across different domains with those of normal hearing (NH) children and to investigate the influence of communication, type of education, and audiological characteristics.

METHODS

This large (N = 252) retrospective, multicenter study consisted of two age- and gender-matched groups: 123 HI children and 129 NH controls (mean age  = 11.8 years). Self-reports were used to measure self-esteem across four domains: perceived social acceptance by peers, perceived parental attention, perceived physical appearance, and global self-esteem.

RESULTS

HI children experienced lower levels of self-esteem regarding peers and parents than NH controls. Particularly HI children who attended special education for the deaf were at risk, even after correcting for their language development and intelligence. Yet, levels of global self-esteem and self-esteem involving physical appearance in HI children equalled those of NH controls. Furthermore, younger age at implantation and longer duration of having cochlear implants (CIs) were related to higher levels of self-esteem.

CONCLUSION

HI children experience lower levels of self-esteem in the social domains. Yet, due to the heterogeneity of the HI population, there is high variability in levels of self-esteem.

DISCUSSION

Clinicians must always be aware of the risk and protective factors related to self-esteem in order to help individual patients reach their full potential.

Behavioral problems in school-aged hearing-impaired children: the influence of sociodemographic, linguistic, and medical factors

The purpose of this study was to examine several behavioral problems in school-aged hearing-impaired children with hearing aids or cochlear implants, compared to normally hearing children. Additionally, we wanted to investigate which sociodemographic, linguistic, and medical factors contributed to the level of behavioral problems, to pinpoint where targeted interventions can take place. This large, retrospective study included a sample of 261 school-aged children (mean age = 11.8 years, SD = 1.6), that consisted of three age- and gender-matched subgroups: 75 with hearing aids, 57 with cochlear implants, and 129 normally hearing controls. Self- and parent-reports concerning reactive and proactive aggression, delinquency, and symptoms of psychopathy, attention deficit hyperactivity disorder, oppositional defiant disorder, and conduct disorder were used. In addition, several language and intelligence tests were administered. Hearing-impaired children showed significantly more proactive aggression, symptoms of psychopathy, attention deficit hyperactivity disorder, oppositional defiant disorder, and conduct disorder than their normally hearing peers. More behavioral problems were associated with special schools for the deaf, sign (-supported) language, hearing aids (in contrast to cochlear implants), higher age, male gender, lower socioeconomic status, lower intelligence, and delayed language development. Hearing-impaired children face multiple problems regarding their behavior. The outcomes implicate that professionals should be aware of the higher risk of developing behavioral problems, in order to screen, detect, and treat in time. Furthermore, the associated risk and protective factors emphasize that clinicians must always consider the heterogeneity of the group of hearing-impaired children, in order to help and support the individual patient.

Psychopathology and its risk and protective factors in hearing-impaired children and adolescents: a systematic review

IMPORTANCE

Pediatric hearing impairment is a chronic handicap that can potentially lead to the development of psychopathology. Yet, for hearing-impaired children and adolescents, the exact occurrence of various forms of psychopathology and its causes are unclear, while this knowledge is essential to enable targeted screenings and interventions.

OBJECTIVE

To investigate the level of psychopathological symptoms in hearing-impaired children and adolescents as compared with normally hearing peers. Second, the influence of type of hearing device and possible risk and protective factors on psychopathology were examined.

EVIDENCE REVIEW

A systematic literature search was performed covering relevant databases, including PubMed, Embase, and Web of Science. Two independent researchers identified the relevant articles. The final search was performed on May 2, 2013, and resulted in a total of 35 articles.

FINDINGS

Literature consistently demonstrated that hearing-impaired children and adolescents were more prone to developing depression, aggression, oppositional defiant disorder, conduct disorder, and psychopathy than their normally hearing peers. Levels of anxiety, somatization, and delinquency were elevated in some, but not all, hearing-impaired participants, for reasons related to sex, age, and type of school. Divergent results were obtained for the level of attention-deficit/hyperactivity disorder and the influence of type of hearing device on psychopathology. Possible risk and protective factors were identified, including age at detection and intervention of hearing loss, additional disabilities, communication skills, intelligence, type of school, and number of siblings.

CONCLUSIONS AND RELEVANCE

Literature on psychopathology in hearing-impaired children and adolescents is scarce and sometimes inconsistent. To define a more precise occurrence of psychopathology, more studies are needed. These studies should have a longitudinal design to draw firmer conclusions on causality. Hopefully, this will lead to more knowledge in the future to help and support each hearing-impaired individual.

Depression in hearing-impaired children

OBJECTIVE

The purpose of this study was to examine the levels of depressive symptoms and the unique contribution of two aspects of emotion regulation (coping and mood states) to the development of depression in hearing-impaired children and a control group.

METHODS

In order to compare the groups, self-report questionnaires concerning symptoms of depression, coping strategies, and mood states were used. The study group consisted of 27 children with cochlear implants, 56 children with conventional hearing aids, and 117 normally hearing children.

RESULTS

Hearing-impaired children reliably reported more symptoms of depression than their normally hearing peers. Degree of hearing loss, socioeconomic status, gender, and age were unrelated to the level of depressive symptoms. But attending mainstream schools or using exclusively speech for communication were related to fewer depressive symptoms. The associations with depressive symptoms differed between the groups. For hearing-impaired children, the cognitive aspects (coping) and the affective aspects (mood states) of emotional functioning contributed separately to the prediction of depressive symptoms. For normally hearing children an integration of cognitive and affective aspects was detected: adequate coping skills prevented the development of negative mood states and in turn depressive symptoms.

CONCLUSIONS

Hearing-impaired children reported more depressive symptoms than normally hearing children. Prevention and treatment of depression in hearing-impaired children could focus on the use of coping strategies adequately, because these strategies have a direct relation with the level of depression.

Hyperacusis in patients with complex regional pain syndrome related dystonia

INTRODUCTION

In complex regional pain syndrome type 1 (CRPS-1), patients may have manifestations of central involvement, including allodynia, hyperalgesia or dystonia. We noted that more severely affected patients may experience hyperacusis, which may also reflect central involvement. The aim of this study was to evaluate the occurrence and characteristics of hyperacusis in patients with CRPS related dystonia.

METHODS

The presence of hyperacusis, speech reception thresholds (SRT), pure-tone thresholds (PTT) and uncomfortable loudness (UCL) was evaluated in 40 patients with CRPS related dystonia.

RESULTS

PTT and SRT were normal for all patients. 15 patients (38%) reported hyperacusis and this was associated with allodynia/hyperalgesia and with more affected extremities. UCLs of patients with hyperacusis were significantly lower than UCLs of patients without hyperacusis.

CONCLUSION

Hyperacusis is common among severely affected patients with CRPS related dystonia and may indicate that the disease spreads beyond those circuits related to sensory-motor processing of extremities.

Evaluation of the Benefit for Cochlear Implantees of Two Assistive Directional Microphone Systems in an Artificial Diffuse Noise Situation

OBJECTIVE

People with cochlear implants have severe problems with speech understanding in noisy surroundings. This study evaluates and quantifies the effect of two assistive directional microphone systems compared to the standard headpiece microphone on speech perception in quiet surroundings and in background noise, in a laboratory setting developed to reflect a situation whereby the listener is disturbed by a noise with a mainly diffuse character due to many sources in a reverberant room.

DESIGN

Thirteen postlingually deafened patients, implanted in the Leiden University Medical Centre with the Clarion CII device, participated in the study. An experimental set-up with 8 uncorrelated steady-state noise sources was used to test speech perception on monosyllabic words. Each subject was tested with a standard headpiece microphone, and the two assistive directional microphones, TX3 Handymic by Phonak and the Linkit array microphone by Etymotic Research. Testing was done in quiet at a level of 65 dB SPL and with decreasing signal-to-noise ratios (SNR) down to -15 dB.

RESULTS

Using the assistive directional microphones, speech recognition in background noise improved substantially and was not affected in quiet. At an SNR of 0 dB, the average CVC scores improved from 45% for the headpiece microphone to 67% and 62% for the TX3 Handymic and the Linkit respectively. Compared to the headpiece, the Speech Reception Threshold (SRT) improved by 8.2 dB SNR and 5.9 dB SNR for the TX3 Handymic and the Linkit respectively. The gain in SRT for TX3 Handymic and Linkit was neither correlated to the SRT score with headpiece nor the duration of CI-use.

CONCLUSION

The speech recognition test in background noise showed a clear benefit from the assistive directional microphones for cochlear implantees compared to the standard microphone. In a noisy environment, the significant benefit from these assistive device microphones may allow understanding of speech with greater ease.

Better Speech Perception in Noise With an Assistive Multimicrophone Array for Hearing Aids

OBJECTIVE

To evaluate the improvement in speech intelligibility in noise obtained with an assistive real-time fixed endfire array of bidirectional microphones in comparison with an omnidirectional hearing aid microphone in a realistic environment.

DESIGN

The microphone array was evaluated physically in anechoic and reverberant conditions. Perceptual tests of speech intelligibility in noise were carried out in a reverberant room, with two types of noise and six different noise scenarios with single and multiple noise sources. Ten normal-hearing subjects and 10 hearing aid users participated. The speech reception threshold for sentences was measured in each test setting for the omnidirectional microphone of the hearing aid and for the hearing aid in combination with the array with one and three active microphones. In addition, the extra improvement of five active array microphones, relative to three, was determined in another group of 10 normal-hearing listeners.

RESULTS

Improvements in speech intelligibility in noise obtained with the array relative to an omnidirectional microphone depend on noise scenario and subject group. Improvements up to 12 dB for normal-hearing and 9 dB for hearing-impaired listeners were obtained with three active array microphones relative to an omnidirectional microphone for one noise source at 90 degrees . For three uncorrelated noise sources at 90 degrees, 180 degrees, and 270 degrees, improvements of approximately 9 dB and 6 dB were obtained for normal-hearing and hearing-impaired listeners, respectively. Even with a single noise source at 45 degrees, benefits of 4 dB were achieved in both subject groups. Five active microphones in the array can provide an additional improvement at 45 degrees of approximately 1 dB, relative to the three-microphone configuration for normal-hearing listeners.

CONCLUSIONS

These improvements in signal-to-noise ratio can be of great benefit for hearing aid users, who have difficulties with speech understanding in noisy environments.

Assessment of a directional microphone array for hearing-impaired listeners

Hearing-impaired listeners often have great difficulty understanding speech in surroundings with background noise or reverberation. Based on array techniques, two microphone prototypes (broadside and endfire) have been developed with strongly directional characteristics [Soede et al., "Development of a new directional hearing instrument based on array technology," J. Acoust. Soc. Am. 94, 785-798 (1993)]. Physical measurements show that the arrays attenuate reverberant sound by 6 dB (free-field) and can improve the signal-to-noise ratio by 7 dB in a diffuse noise field (measured with a KEMAR manikin). For the clinical assessment of these microphones an experimental setup was made in a sound-insulated listening room with one loudspeaker in front of the listener simulating the partner in a discussion and eight loudspeakers placed on the edges of a cube producing a diffuse background noise. The hearing-impaired subject wearing his own (familiar) hearing aid is placed in the center of the cube. The speech-reception threshold in noise for simple Dutch sentences was determined with a normal single omnidirectional microphone and with one of the microphone arrays. The results of monaural listening tests with hearing impaired subjects show that in comparison with an omnidirectional hearing-aid microphone the broadside and endfire microphone array gives a mean improvement of the speech reception threshold in noise of 7.0 dB (26 subjects) and 6.8 dB (27 subjects), respectively. Binaural listening with two endfire microphone arrays gives a binaural improvement which is comparable to the binaural improvement obtained by listening with two normal ears or two conventional hearing aids.

Development of a directional hearing instrument based on array technology

A directional hearing aid might be beneficial in reducing background noise in relation to the desired speech signal. Conventional hearing aids with a directional cardioid microphone are insufficient because of the low directivity of cardioids. Research was done to develop microphone(s) with strong directional characteristics using array techniques. Particular emphasis was given to optimization and stability. Free-field simulations of several robust models show that a directivity index of 9 dB can be obtained at the higher frequencies. Simulations were verified with a laboratory model. The results of the measurements show a good agreement with the simulations. Based on simulations and measurements, two portable models were developed and tested with a KEMAR manikin. The KEMAR measurements show that the two models give an improvement of the signal-to-noise ratio of approximately 7.5 dB in a diffuse sound field. It may be concluded that the developed microphones have the capability to reach a significant improvement of speech intelligibility in noise under practical circumstances.