18.3.1 Need for Family-Centred Early Intervention After Diagnosis of Hearing Loss (HL)

Newborn hearing screening (NHS) programmes and the early provision of hearing aids have improved the perspective of children with HL to develop the best possible speech-language and auditory skills. However, the early detection and the early provision of technical aids are not considered to be sufficient for successful speech-language development. Another significant factor is the early start of a family-centred early intervention that highlights the parents’ central role in their child’s communicative development (Moeller 2000; Holzinger and Fellinger 2013; Sarimski et al. 2013). Following the modern paradigms in early intervention and the guidelines for best practice of hearing-impaired infants, the focus should be on family-child interaction, rather than on child-directed therapy (Moeller et al. 2013).

Normally, for hearing parents, the diagnosis HL is unexpected. It may irritate parents in their communicative interaction with the infant and can impede their intuitive parental skills (Koester and Lahti-Harper 2010). However, a language-rich stimulation during natural interaction is most influential for successful communication development of children with HL (Szagun and Stumper 2012). Parents themselves wish for early and close-meshed support after the diagnosis (Young and Tattersall 2007).

18.3.2 The Muenster Parental Programme (MPP)

The MPP (see Fig. 18.3) is an evidence-based responsive parenting intervention specific to the needs of parents of infants with HL identified by newborn hearing screening (NHS) (Reichmuth et al. 2013; Glanemann et al. 2013). The concept of the MPP draws upon current research findings concerning early speech and language development of normally hearing children and of children with HL. It follows the principle of communication-orientated and natural auditory-oral approaches for children with HL. These concepts emphasise the importance of natural parent-child communication in everyday life (e.g. Batliner 2012; Clark 2007). The MPP incorporates essential elements of existing responsive parenting programmes for normally hearing children that focus on parents’ communication towards their child (international overview by Brady et al. 2009). These elements have been extended and modified to satisfy the needs of families who have a child with HL. Moreover, the MPP matches the demands of national (German) and international guidelines (Moeller et al. 2013; DGPP 2013).

Fundamentally, the MPP follows two main goals in optimising the conditions for the child to develop the best possible speech-language competence. First, parents get reinforcement concerning their intuitive parental skills and competences – especially in being responsive – and they are supported in communicating and interacting with their child (see Fig. 18.4). In working with the parents, the programme is respectful of individual differences and recognises each family’s strengths and natural skills. Second, the group sessions allow early contact and exchange with other families and offer mutual social and emotional support.

The MPP is a short intervention of 3 months and combines six multifamily parent-group sessions with four single-family parent sessions. It is designed for parents of hearing-impaired children who are at the preverbal level and who do not yet use words (age 3–18 months). The children may have a risk of an additional developmental delay. If the child is a candidate for cochlea implantation, the MPP serves as a valuable activity to bridge the time until implantation. Parents can already establish a sound basis for successful parent-child communication. Following the implantation parents can build on what they have experienced and learnt during the preoperative period.

In small groups without children, parents learn about communicative strategies, such as responsiveness, which nurture their child’s speech-language and auditory development (see Reichmuth et al. 2013 for more details on further contents). In two of the single sessions, parents learn to recognise their child’s communicative attempts and to be responsive to them. Here, they are guided by means of individual video feedback to employ and intensify responsive strategies in the interaction with their child. By this, parents often realise that they already use a great part of these strategies and (re)start to appreciate their own parenting skills.

In addition to the 3-month programme in early infanthood, there is an individual refresher session with video feedback when the child is at the early verbal stage, around 24–30 months of age. Embedded in dialogic picture book reading, as a typical and joyful interactive situation at that age, parents learn to transfer the MPP strategies to the now raised verbal level of their child (see Reichmuth et al. 2013 for more details on this concept).

18.3.3 Study Results

The accompanying study (prospective group design) showed by video analysis that parents who participated in the MPP could intensify their communication-enhancing behaviour towards their child more than parents of a control group (see Figs. 18.5 and 18.6). Moreover, at the end of the 3-month programme, children of participating parents vocalised more than children of the control group (see Fig. 18.7).

The feedback from participating parents was very affirmative. Specifically, they valued the exchange with other parents of affected children and the individual single sessions with video feedback. Altogether, they would recommend the MPP to other parents in a comparable situation (Glanemann et al. 2016).

The evidence-based Muenster Parental Programme fulfils the demands of modern family-centred early intervention (Moeller et al. 2013) and is a module of comprehensive early intervention. As such it can be recommended after early identification of HL.

18.4.1 Introduction

The aim of a hearing aid fitting is to make sounds and especially speech audible for the hearing-impaired person. As most people with a sensorineural hearing loss have a limited hearing range between their hearing threshold and their uncomfortable loudness threshold, the amplified sound has to be compressed into the remaining dynamic field so that soft sounds can be heard again and loud sounds do not get uncomfortably loud. To make a hearing aid wearable, it is also necessary to miniaturise the electronic components (see Fig. 18.8), including the microphone and receiver, as much as possible, but that still implies a number of restrictions especially concerning the sound quality and the bandwidth of the receiver. Therefore a certain amount of hearing loss is necessary for the unavoidable degradation of the sound passing through the miniature components of the hearing aid to be outperformed by the benefit that can be achieved through the amplification of the sound.

The individual hearing and communication needs, the degree and the configuration of the hearing loss and a careful review of the achieved benefit have to be considered in combination with a rigorous fitting and verification protocol for a hearing aid to be successful.

18.4.2 Audiological Candidacy and Audiometric Preconditions

The basis for any hearing aid fitting is an as precise as possible audiometric evaluation, including a frequency-specific threshold. Whenever possible these data should be completed by an estimate of the residual dynamic range, speech audiometric data and a measurement of acoustic characteristics of the outer ear and ear canal. The extent of individual audiometric data that can be collected will depend on the hearing-impaired person’s ability to cooperate.

Depending on the size of the ear canal and the air volume under the headphone, or between the tip of the ear mould and the eardrum, the sound pressure level at the eardrum differs from the reading at the dial of the audiometer. The sound pressure level will be higher at the eardrum for the smaller ear canals of children than at the bigger ear canals of adults. These differences can be calculated by taking into account the transfer characteristics of the transducer together with a measured correction factor for the individual ear canal. This calculated sound pressure level at the eardrum should then be the starting point for the programming algorithm of the hearing aid. For the verification process, it is additionally necessary to convert threshold data and measured hearing aid performance into the same scale unit (Fig. 18.9). For this purpose the data are mostly converted to dBSPL.

For children the programming algorithm also has to incorporate additional gain that is needed to give children enhanced audibility of speech sounds for their language acquisition, as they still do not have the capacity to “fill in the blanks” for inaudible sounds in the way that adult listeners do (American Academy of Audiology 2013).

As they still have to acquire their language skills, a hearing aid fitting should also be considered for children with very mild hearing losses of less than 30 dB and for children with unilateral hearing loss. After a trial period, the long-term provision of the hearing aid can only be justified if it can be proved that usable gain is provided and that a benefit in audibility can be expected.

For deaf children with additional needs, the assessment and the fitting should be provided by an experienced multi-professional team. For some of these children, the effect of their hearing loss on their development will be intensified by their additional handicaps, but for others hearing may be not their most urgent priority, or they may be very sensitive and easily overwhelmed by too much sound that they cannot differentiate.

18.4.3 Preparation of the Audiometric Data for Hearing Aid Fitting to Young Children

For the necessary conversions, some pre-existing correction factor tables can be used, such as dBHL to dBSPL, or the CDD values (coupler-to-dial difference), which are for a given transducer the difference between the audiometer dial reading and the corresponding sound pressure level in a 2 cc-coupler (which is used for measuring hearing aids). Other correction factors have to be measured individually, such as the RECD (real ear-to-coupler difference), which is the individual difference between the sound pressure level in the patient’s ear canal and that of the same sound delivered to a 2 cc-coupler (Fig. 18.9). The RECD can even be measured in babies, but average RECD values for monthly age intervals are available (DGPP 2012; Western University of Ontario National Centre for Audiology 2014). To keep the necessary corrections as small as possible, it is highly recommended to use insert earphones for measuring tone audiometry as well as ABR thresholds with children.

By combining these correction factors, threshold values in dBHL from the audiometer (or ABR) can be converted to the corresponding dBSPL at the eardrum. When using ABR threshold data, one additionally has to bear in mind that, depending on the kind of stimulus (e.g. click, toneburst, notch-noise, chirp), the kind of method (classic ABR or ASSR) and the type of machine, the results will vary in regard to how close they get to the “real” threshold in different frequency areas. So for tonebursts or for most ASSR measurements at low frequencies such as 500 Hz, threshold levels that are 30 dB (±20 dB) louder than the “real” threshold are common. Therefore the use of frequency-specific corrections to get from the dial reading of the ABR machine (dBnHL decibel above normal adult hearing) to an estimate of the “real” threshold is necessary (Fig. 18.10). These corrections will differ from clinic to clinic (depending on their equipment) and can therefore only be performed by the professional who did the ABR measurement. But the final threshold estimate that will be used for the hearing aid fitting should not only include the data from the ABR but also a summary of all the audiometric data available at the end of the diagnostic process. The threshold estimate should be as close as possible to the threshold in dBHL that would be expected from the hearing-impaired person if he were able to cooperate fully in a tone audiometry procedure. These values can then be used in the hearing aid fitting software without further “ABR corrections” provided by the fitting software itself (this function must then be disabled in the software!).

18.4.4 Types of Hearing Aid

Hearing aids can be classified in very different ways, by the:

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  Style of wearing: behind the ear (BTE), in the ear (ITE), in the ear canal (ITC), attached to glasses, body-worn, bone-anchored, partially or fully implanted (see Fig. 18.11)

  
  
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  Amount of gain and maximum output

  
  
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  Type of amplification: analogue, digital programmable, digital

  
  
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  Type of sound processing: linear, compression, wideband compression, the number of frequency and compression channels, the number and kind of sound-processing programmes for different hearing situations, the way of switching between these programmes

  
  
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  Type of receiver and the way of coupling the receiver to the ear: air conduction with standard tube and ear mould, with slim-tube, open fitting, external receiver in the ear canal, bone conduction

  
  
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  Routing of signals: monaural, bilateral, contralateral routing of signal (CROS) with a microphone on the worse hearing side and the receiver in an open fitting on the better (normal)-hearing side or BiCROS with a microphone on both sides connected to one receiver on the better-hearing side

  
  
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  Additional features that are available in a hearing aid: directional microphones, noise reduction, feedback cancellation

  
  
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  Special features for children: a switch and volume control that can be deactivated, a tamper-proof battery compartment, moisture-resistant, an LED indicating the functioning of the hearing aid

In regard to the complexity of many digital hearing aids with a high number of additional features and the option of attaching further hearing devices directly to the hearing aid (streamer, FM systems, telephones, etc.), many professionals today prefer the term “hearing system” instead of “hearing aid”.

The most widely used hearing aids in Europe are fully digital hearing aids with multi-frequency and multi-compression channels. For children up to primary school age, it is reasonable to use BTE hearing aids (American Academy of Audiology 2013), as they are the most robust devices and the ear moulds can be easily exchanged whenever the child grows and the ear mould starts leaking sound and produces feedback problems.

18.4.5 Types of Ear Mould

Ear moulds are necessary to channel the sound into the ear canal and to retain the hearing aid at the ear. The higher the gain of the hearing aid, the tighter the seal of the ear mould must be, to prevent feedback (whistling) (Fig. 18.12a). The length of the ear canal part of the ear mould determines the air volume that is left in front of the eardrum, and the smaller this volume is, the higher the sound pressure level at the eardrum becomes. The length, the diameter and the shape of the tubing in the ear mould influence significantly the frequency transmission into the ear canal. Therefore the ear mould is a part of the overall sound transmission of the hearing system, and it can enhance or degrade the performance of a hearing aid. So the effect of the ear mould has to be taken into account with any verification process.

Ear moulds can be classified for their shape and function (Fig. 18.12a–g). Ear moulds may be “vented” by a second borehole in the ear mould that reduces the occlusion effect (complaints of fullness in the ear) and warms and ventilates the otherwise quite humid space between the ear mould and the eardrum. Especially in any case of otitis externa, a humid chamber may further enhance the growth of bacteria and fungi in the ear canal.

Hearing loss of a lesser degree allows open ear mould fitting, which reduces the amount of occlusion and the contact to the skin of the ear canal and the pinna (Fig. 18.12b, c). Feedback cancellation systems or an increased distance between microphone and receiver may be necessary to avoid whistling artefacts.

For children the ear mould should be made from soft (normally silicone) material. In case of an allergy against one of the ear mould materials, there are alternative hypoallergenic materials available as well as special coatings (such as gilding of the ear mould or titanium ear moulds, Fig. 18.12d, e). For more than moderate hearing losses, the length of the ear canal part should reach the second bend of the ear canal (American Academy of Audiology 2013; BIAP 2012), and the outlet of the ear mould must point in the direction of the eardrum. As children grow and the softer tissue of a child’s ear will widen initially by the use of the ear mould, it may be necessary to renew ear moulds in babies every few weeks (BIAP 2012; DGPP 2012; Western University of Ontario National Center for Audiology 2014). Well-fitted and well-sealed ear moulds for babies with high-power hearing aids can prove to be a piece of art that needs a lot of experience and dedication.

A better sealing may be reached by a thermoplastic material (e.g. THERMOtec, Fig. 18.12f), which softens at body temperature, but it is more expensive, and because of the surface condition, more intensive cleaning (disinfection, ultrasonic cleaning) is necessary.

Ear moulds are available in many colours and with applications (e.g. comic motives or strass stones) suitable for children (Fig. 18.12g).

Please keep in mind that the making of any good ear mould starts with a perfect impression. During impression taking, penetration of the impression material in the middle ear through an unintended or pre-existent perforation of the eardrum is rarely reported but should strictly be avoided by careful handling and use of protective means in the ear canal, especially in patients with eardrum perforation or a tympanostomy tube (Silva et al. 2015).

As babies and young children cannot themselves complain specifically about hearing aid or ear mould problems that bother them, a tight quality control by the professionals is necessary. If there is any question of whether the sealing effect of an ear mould is sufficient, the seal of an ear mould should be measured. The necessary devices are available from the quality control measurements for noise protectors.

18.4.6 Selection and Fitting of the Hearing Aid

The degree and type of hearing loss will determine the amount of gain and maximum output level that is needed to make speech audible again. The age, the living conditions and the personal requirements of the hearing-impaired person will affect the choice of hearing aid type and hearing aid features. For children a robust hearing aid with a reliable repair service, a tamper-proof battery compartment, a volume control and switch that can be deactivated, a water-resistant shell and a direct audio input port to attach an FM receiver would be a suitable choice. It should be a digital, multichannel compression device (>4 channels) with a feedback-cancelling algorithm that does not affect the overall gain of the hearing aid.

Any person with bilateral hearing loss should be fitted bilaterally with hearing aids. There may be exemptions to this rule if it can be shown in the validation process that the second hearing aid compromises the hearing and understanding through the leading ear. In cases of asymmetrical losses, one should try to use the same hearing aid model on both sides. In the case of very asymmetrical losses, it may be necessary to use a more powerful hearing aid on the poorer hearing side, but it has to be shown that this hearing aid provides at least some benefit. With very young children, that proof of a benefit may not be achievable; therefore one may try to fit a hearing aid on the worse side as long as it is tolerated and does not provide feedback problems. In case of a profound hearing loss on the worse side, one may also consider a bimodal intervention with a cochlear implant on the profound side and a hearing aid on the better-hearing side.

(See also the paragraph “special issues”.)

18.4.7 Selection of Hearing Aid Features

It seems to be that in the recent past, more professionals are tending to follow the argument of the second group, for a more active use of the advanced features of hearing aids even with very young children, and especially utilising directional microphones and noise reduction systems. For the fitting of frequency-lowering techniques, see also the paragraph “verification”. The use of directional microphones should not be started until the baby is more upright and no longer lying most of the time in its bed; otherwise the contact of the directional microphones with the pillows may add a lot of rubbing noises to the hearing signal.

As children and especially very young children are not able to switch between different hearing aid programmes according to their actual needs in different hearing situations (such as quiet, noisy, multi-talker background, music, external wireless microphones, etc.), they need a precise-as-possible automated classification of the hearing situation and an automatic adaptation of the hearing aid mode/programme to the hearing situation. Studies seem to indicate that children need different classification boundaries for switching the hearing aid mode than do adults and that these special needs for children may even be age-dependent. Manufacturers are just starting to implement these findings into their fitting algorithms.

As most children in Europe get good-quality hearing aids, but not the high-end hearing aids, the features that are available in the mid-range hearing aids are less sophisticated, or some of them even unavailable, compared with the hearing aid models that were used for the scientific studies. But with fewer frequency channels and reduced classification capabilities, even the features still available may be less useful or produce more side effects than the more sophisticated algorithms in the hearing aids used in the studies. So for directional microphones, only adaptive systems are acceptable that ensure in quiet situations that directionality is switched off and in noisy situations that dominant speakers located to the side of or behind the child can also be understood. To minimise any negative effect on the speech perception of the child, noise reduction systems need as many frequency channels as possible that can be separately regulated and a very good child- and age-related hearing situation classification algorithm that can make use of a variety of specialised hearing programmes. These necessary requirements tend to be only available in the most advanced (and therefore most expensive) high-end hearing aids. Until now it is an open question in most countries how this technology can be made available to all or at least most children. If only limited automated algorithms are available in a hearing aid, the risk increases for a number of hearing situations that inappropriate features may be activated by the hearing aid. For these hearing aids, it may be more advisable to restrict the activation of features such as directional microphones or noise reduction systems to an often difficult case-by-case decision.

Some help for making the decision on whether and how to fit advanced data-logging algorithms may come from the data logging system of the hearing aids. Data-logging can provide an overview about the distribution of hearing situations that the child is confronted with in daily life (percentage of time in a quiet environment, in a noisy environment, in a multi-talker environment). An even better overview of the listening environment of children can be achieved by using sound recordings and communication analysis by the LENA system (LENA Research Foundation 2016).

18.4.8 Verification

Any hearing aid fitting requires a verification that the prescribed target gain, frequency range and prescribed maximum output levels are achieved for the individual conditions in the ear canal of the client. It has to be proved that the long-term average speech spectrum is made audible again. Such a technical control of the hearing aid performance is indispensable, especially when fitting hearing aids to children, as validation measurements are much more difficult and less reliable than with adults. Audibility and how well the hearing aid output data match the prescribed targets can be best evaluated when targets, output data and the hearing threshold of the patient are displayed in one graph. Such a display can be achieved with an SPLogram or with a percentile measurement (Fig. 18.13).

As most advanced hearing aids use speech-sensitive processing algorithms, it is necessary to use speech itself as a stimulus for the verification measurements, such as the International Speech Test Signal ISTS (American Academy of Audiology 2013; BIAP 2012; DGPP 2012). With this signal the performance of the hearing aid for soft, moderate and loud speech can be tested. For testing the maximum output tonebursts, warble and sinus tones at 90 dB are used. With these the maximum output level of digital multi-compression hearing aids may be underestimated; therefore more suitable broadband test signals are in preparation.

The SPLogram or the percentile measurement also provides a unique opportunity for a well-controlled and well-targeted approach for finding the cause of complaints by the client or a rejection of a hearing aid by a child. These measurements will also provide the necessary data to enhance certain frequency areas when the speech audiometry, speech testing or the speech development shows deficits for some speech sounds.

18.4.9 Validation

All these tests may provide valuable information about the performance and benefit, or the still remaining deficiencies, of a hearing aid fitting. But each of these tests has its strengths and pitfalls.

As any audiometry testing with the hearing aids can only provide data that are limited by the special and sometimes quite “artificial” test circumstances, the validation procedure must include a good anamnesis of the hearing performance and difficulties in daily life, as well as any concerns about the use of the hearing aids. The anamnesis can be supported by a questionnaire in the form of a structured interview. Questionnaires are also an efficient way of obtaining information about the progress of the child with the hearing aids from other team members, and they permit a good opportunity to monitor the progress of a hearing aid fitting process.

Memory box: A hearing aid fitting of children should only be finalised if audibility of speech sounds is secured as far as possible. This has to be documented by a measurement of the hearing aid output in relation to the child’s hearing threshold and the child’s uncomfortable loudness threshold (e.g. through an SPLogram or percentile measurement). The hearing aid benefit must be additionally validated by audiometric tests (speech audiometry and aided thresholds) as well as reports by the child’s caregivers.

18.4.10 Interdisciplinary Cooperation

Audiological assessment, hearing aid fitting and early intervention have to be a part of a holistic family-centred approach to meet the needs of a hearing-impaired child and its family. All stakeholders in this approach have to cooperate closely and transparently. Everyone has to ensure that the other professionals receive information and data that they need to fulfil their task timely and in a way that the data can be used with a minimised risk of misinterpretation. Any doubts and criticism should be exchanged directly and respectfully among the professionals. The different supplementary points of view can provide the opportunity of self-control and self-reflection. Such interdisciplinary cooperation also provides valuable self-protection in the difficult assessment and intervention process, so that needs of improvement and change can be identified as early as possible. Important steps in the intervention process, such as finalising the hearing aid fitting, suggesting a cochlear implantation or changing the mode of communication, should be taken in consent with the other professionals involved.

18.4.11 Special Issues

Therefore it is necessary always to crosscheck all test results, e.g. ABR versus VRA or BOA data, and the audiometric data versus reports about hearing reactions by the parents! Only a conclusive summary of all these data sources can be an acceptable basis for a diagnosis and basis for a hearing aid fitting.

Concerning the amount of amplification, one may have to consider that multiple disabilities may magnify the effect of hearing loss and therefore emphasise the need of compensation, but some of these children can also get more easily overwhelmed by sound and noise as they are less able to pick and listen selectively to the relevant sound source in a noisy environment. A well-documented verification of the applied gain and output characteristics provides the necessary data for a targeted fine-tuning of the hearing aid according to the needs, reactions and acceptance by the child.

These children can be highly selective in the sounds they are reacting to. Therefore listen to the family and ask about sounds that are familiar and of interest to the child. Try to integrate these sounds into your hearing evaluation (with and without hearing aids).

Please also keep in mind that for some multi-handicapped children, their hearing problem may be an important but not the most urgent problem the families have to deal with first, so that diagnostic procedures and hearing rehabilitation efforts have to be postponed. But even then keep in touch with family, and try to find the most appropriate way of assessment and support for this family.

18.5.1 Implantable Hearing Aids

Today, the majority of all implanted hearing aids are semi-implantable, i.e. they consist of an implanted part, always containing at least the interface, which delivers acoustic energy to some part of the ear or the skull of the user, and an externally worn part, which contains at least the energy source of the device, the microphone and an interface, which allow communication with the implanted part. From the considerable number of devices that have been developed and presented so far, the majority has been abandoned, and only a few systems have been implanted in more than 1000 users. However, implantable hearing aids are a very active area of research, so new designs and devices can be expected to become available in the future.

Today, implantable or semi-implantable hearing aids of the type described by (a) that drive the ossicular chain are used only relatively rarely in children. At some centres, they are used to treat aural atresia in children. Currently, however, at most centres even for this indication, one of the solutions of type (b) discussed further below is preferred. Indications for cochlear implants (c), finally, will be covered in Sect. 18.6.

18.5.2 Bone-Conduction (BC) Hearing Aids

BC hearing aids can be subdivided into implantable and non-implantable systems, both of which are used regularly in children (McDermott and Sheehan 2011). Some special features are shared by both kinds of system; some are specific to either implantable or non-implantable systems.

18.5.2.2 Non-Implantable Bone-Conduction Hearing Aids

Non-implantable BC hearing aids are easy to use and can be fitted quickly in children. No surgery is needed, and several different systems from different manufacturers, as well as a number of methods to attach the transducer to the head of the child, are available (Verstraeten et al. 2009). Figure 18.14 shows a girl wearing a BC aid on a softband, and Fig. 18.15 a shows the same aid attached to a headband. At some centres, BC hearing aids are not fitted much before the age of approximately 6 months, as indentations in the softer skull of very young children are more frequent. A number of current systems are shown in Figs. 18.14 and 18.15. They include strictly non-implantable devices, such as the contact mini (BHM Inc., Figs. 18.14 and 18.15a), the Ponto series devices (Oticon Medical, Fig. 18.15b) and the Baha series devices (Cochlear Inc., Fig. 18.15c), which can be used either with headbands, softbands or implants.

Currently, new systems are introduced frequently. Figure 18.16 shows two recent additions. In the ADHEAR system (MED-EL Inc., Fig. 18.16a), an adhesive adapter is placed behind the ear and can stay there for several days, before it is replaced by a new adhesive adapter. An audio processor is then snapped on the protruding adapter pin of the adhesive part. In the SoundArc System (Cochlear Inc., Fig. 18.16b), a sound processor is attached to a flexible arc, which is worn just above the ears and passes behind the head of the user, thus improving the cosmetic aspect considerably, when compared to the softband or the headband. One or two processors can be worn on the same arc.

Acoustic overstimulation of the inner ear is not possible with any of the current devices.

18.5.2.3 Implantable Bone-Conduction Hearing Aids

Currently, three basic types of implantable BC hearing aid are available. The oldest principle, the bone-anchored aid, has now been used for over 35 years. It consists of a percutaneous titanium implant to which an external sound processor is attached (Kurz et al. 2013). Figure 18.15b, c shows current sound processors, and Fig. 18.16b shows a model of such a system.

For the second type of implantable BC hearing aid, the same sound processors can be used, but the coupling to the skull is transcutaneous (Kurz et al. 2014). An implanted magnetic plate is connected to the skull and attracts an external magnetic plate, to which a sound processor is attached. The skin between the two magnetic plates remains intact and results in a small attenuation predominantly at frequencies above 2 kHz. Figures 18.15d and 18.17 a show the external components of such a transcutaneous system.

Similarly, the skin remains intact in the third type of implantable BC-device, shown in Fig. 18.15e, f (Zernotti and Sarasty 2015). Here, the transducer is implanted and is therefore attached directly to the skull, ensuring good acoustic coupling.

For children with a perfect inner ear function, the performance of these three types of implantable BC hearing aid can be expected to be comparable.

18.6.1 Cochlear Implantation: Basic Principles

Cochlear implantation is an accepted method of treatment for children and adults with severe-to-profound hearing loss who derive insufficient benefit from conventional hearing devices (Wilson and Dorman 2008; Holden et al. 2013). A cochlear implant (CI) evokes auditory sensation via direct electrical stimulation of the auditory pathways by converting acoustic signals into coded electrical pulses. These electrical pulses stimulate nerve fibres in the cochlea. The auditory nerve transmits the signals to the brain where they are interpreted as sounds (Clark 2003; Peterson et al. 2010).

A CI consists of internal components, which are surgically implanted under the skin, and external components, which are worn behind the ear (Fig. 18.18).

CI provision is not limited to the surgical issue of implantation which is presented in Sect. 18.24.

CI provision includes careful preoperative (ped)audiologic assessment and counselling and post-operative (re)habilitation. The latter starts with the initial fitting of the implant and covers a period of 2–3 years, depending on the CI user’s age and communication status.

18.6.2 Cochlear Implant Technology

Components

The internal components of a CI, which are surgically placed under the skin behind the ear, consist of (1) the implant, including the receiver and the magnet, and (2) the electrode array, including the electrode contacts. The implant contains the electronic device for signal processing. The electrode array is surgically placed within the cochlea and contains 12–22 electrodes for stimulating the nerve fibres within the cochlea. The external components are worn behind the ear and consist of the sound processor with microphone, the battery pack, the coil, the magnet and a cable connecting the sound processor and the coil. The sound processor contains the electronic device for signal processing (Zeng et al. 2008). The external coil is held in place behind the ear via external and internal magnets (Fig. 18.19).

Signal Processing

The starting point of signal processing is the microphone of the external sound processor, which converts acoustic sound into an electrical signal. The electronic device of the sound processor analyses and codes this signal into a special pattern of digital information by using a coding strategy. The coil transcutaneously transmits the coded electrical signal to the receiver. The internal electronic device decodes the transmitted signal and forwards it to the electrode array by means of specific electrical pulses of individual electrodes. These electrical pulses stimulate the nerve fibres within the cochlea (Rubinstein 2004). The aim of the signal processing of the cochlear implant is to produce electrical stimuli which closely resemble the stimuli that intact hair cells would produce with the same acoustic input. Hearing perception depends on the characteristics of the electrical stimulus and on the place of the stimulation. Accordingly, CI technology uses certain characteristics of signal processing/stimulating and the tonotopic organisation of the cochlea.

The tonotopy of the human cochlea describes the relationship between frequency and place of stimulation, meaning that an acoustic signal with a specific frequency results in the stimulation of auditory nerve fibres in a specific region of the cochlea (Greenwood 1990). The basal part of the cochlea is associated with high frequencies, and the apical part of the cochlea is associated with low frequencies (see Fig. 18.20). Accordingly, cochlear implants map high frequencies to basal electrodes and low frequencies to apical electrodes (Oxenham et al. 2004).

Cochlear implants can cover a frequency range of approximately 100–8500 Hz, in which each electrode is assigned to a certain frequency band. For example, for spectral fractionising, a frequency range (188–7938 Hz) is assigned to 22 frequency bands. The final amplitude of the electric current pulse of a specific electrode is proportional to the energy of the amplitude of the acoustic input of the associated frequency band. Here mainly the signal amplitude changes over time, the so-called envelope information is taken into account, whereas the spectral information is largely reduced. In most cases, the shape of the electrical stimulus is a charge balanced biphasic pulse. The duration of the electrical pulses is very small (usually <50 μs). The characteristic of the signal processing for converting the acoustic input to the final electrical stimulus is defined by the coding strategy. Various coding strategies are available, for example, ACE (advanced combination encoder), CIS (continuous interleaved sampling), SPEAK (spectral peak coding), HiRes120 (high-resolution fidelity—120 virtual channels), FSP (fine structure processing) and FS4 (fine structure processing on 4 channels).

Figure 18.21 shows the colour-mapped intensity of the electrical pulses for the acoustic signal corresponding to the spoken German word “Zeit” (tsa͜it). Here the signal coding strategy ACE (advanced combination encoder) was used, segmenting the acoustic signal into 22 frequency bands. For each time instant, the frequency bands that feature the highest acoustical energy were chosen in order to stimulate the associated electrodes simultaneously. The colour mapping illustrates the intensity of the electrical stimulus according to the intensity of the acoustic signal, specified as a percentage of the dynamic range (DR) of each electrode. The colour-mapped intensity is a relative (%) not an absolute value. The absolute intensity of this current flow is an individual quantity which has to be determined for each CI user and for each electrode individually. This process is called cochlear implant fitting (see next section).

18.6.3 Cochlear Implant Fitting

Hearing through a CI differs greatly from normal hearing, and the (re)habilitation process and the ultimate performance show great variability across CI users (Peterson et al. 2010). Adequate fitting of the CI is the centrepiece of this gradual process. It is important to emphasise that these fitting processes require parallel aural rehabilitation approaches that include speech and language therapy, psychosocial support, etc. Thus, post-operative therapy entails more than just regular fitting sessions. This is particularly true for children, who should participate in multidisciplinary (re)habilitation programmes for the entire period of their speech and language development. However, adults also need support by therapists of different professional backgrounds to become accustomed to the changing hearing impressions over time.

Basically, cochlear implant fitting means determining a CI user’s Threshold (THR or T-Level) and Maximum Comfortable Level (MCL or C-Level) for each electrode referring to the electrical current flow and the duration of this current flow for each individual electrode (Shapiro and Bradham 2012). Figure 18.22 shows a screenshot of the fitting software “Custom Sound”. To determine the MCL and THR of individual channels, single electrode stimulation is performed within the fitting section. MCL is defined as the current flow which produces a loud but still comfortable perception when stimulating a certain electrode (or the maximum loudness of the comfortable region). The corresponding THR is defined as the current flow at the hearing threshold (a current flow less than the THR is not perceptible for the CI user). An objective measurement of neural responses to electrical stimulations—neural response telemetry (NRT)—can support the fitting procedure. Normally, the first fitting procedure is executed about 3 weeks after implantation. Since the perception of these pulses is not consistent over time, it is necessary to repeat the fitting procedure regularly. This reflects the learning process that occurs as the CI user becomes increasingly accustomed to stimulation through the implant. Thus, after the initial fitting of the CI, CI users will need to return to the CI rehabilitation centre regularly for subsequent refitting within the (re)habilitation paradigm. Frequent refitting is required, especially during the first year of implant use. After the first year, less frequent sessions will be required. Later on, most CI users continue to require occasional adjustments (yearly or twice a year) for as long as they use their implant.

18.6.4 Candidacy and Indication in Children

The implementation of universal newborn hearing screening has been enhancing the prospects of early clinical diagnostics and therapy of hearing-impaired infants. As early intervention facilitates speech and language acquisition, physicians specialised in communication disorders, notably paedaudiologists, are challenged to provide reliable diagnosis within the first months of life. With respect to early cochlear implantation, an essential concern is the issue of diagnostic specificity and reliability in young infants: the risk of implanting a child without severe-to-profound hearing loss (Sampaio et al. 2011).

High standards and multidisciplinarity are therefore crucial for the assessment of candidacy for v implantation, and the final recommendation should be given by an experienced council of specialists. The diagnostic procedure needs to be appropriate to the developmental status and to the age of the child. Thus, audiometric assessment should include behavioural observation audiometry, visual reinforcement audiometry, play audiometry or pure-tone audiometry. Electrophysiological testing incorporates tympanometry, stapedial reflex measurements, otoacoustic emissions, frequency-specific ABR or auditory steady-state responses (ASSR).

As ABR thresholds can change, at least two ABR measurements should be performed before initiating a cochlea implantation (Louza et al. 2016). Special attention is mandatory for infants treated in the neonatal intensive care unit, who often show a significant improvement of ABR thresholds in their development in comparison to the initial ABR measures (Morimoto et al. 2010).

For a detailed description of audiometric and electrophysiological testing, see Chap. 16. Since most of the infants with hearing loss initially receive hearing aids, verification measurements are essential to compare the performance with and without hearing aids (see Sect. 18.4). Further assessment includes diagnostic interviews of parents, age-related detailed evaluation of verbal and non-verbal communication skills (see Sect. 16.​16) and the estimation of the general cognitive developmental stage (see Sect. 16.​18). Another major aspect of candidacy assessment is the radiological examination of the cochlea and auditory pathway with particular consequences in cases of cochlear malformation (see Sect. 16.​21). An extended individual diagnostic procedure needs to be provided for children with multiple disabilities (see Sects. 16.​23 and 16.​24). Generally, the interdisciplinary diagnostic approach described allows a confident assessment of a child’s hearing loss within the first 12 months of life, including a hearing aid trial.

In principle, there is an indication for cochlear implantation for individuals with severe-to-profound hearing loss who obtain little or no benefit from acoustic amplification in the best-aided condition and show no progress in spite of auditory training and speech and language therapy. In contrast to the former requirement of bilateral deafness, most devices now are approved for use in patients with severe-to-profound hearing loss, even including asymmetric and unilateral losses. The above-mentioned interdisciplinary diagnostic approach clarifies that candidacy not only depends on audiometric findings. Age and developmental status also determine the relevance of the different measures for decision-making. For example, electrophysiological measures, in particular frequency-specific ABR and prelinguistic evaluation of communication skills, are of special importance in candidacy assessment in infants after 9–12 months of life with congenitally profound hearing loss. In contrast, in a toddler with progressive hearing loss, a detailed evaluation of the different levels of speech communication might be of particular importance to assess the handicaps’ severity. With regard to the developmental status, it is important to understand that ABR may fail in preterm children in the first months of life and in other children with disturbance of brain function or retarded maturation. Since reversible ABR abnormalities are common among neonates and infants at high risk of hearing loss, a control ABR some months later or repetitive measurements are necessary for precise threshold assessment (Psarommatis et al. 2017).

Recent publications have suggested guidance values with respect to mean pure-tone thresholds in unaided conditions. These authors recommend that children presenting with pure-tone thresholds worse than 75–85 dB HL should be considered as candidates for cochlear implantation (Leigh et al. 2011; Lovett et al. 2015). In cases of bilateral severe-to-profound hearing loss, bilateral cochlear implantation is recommended. Apart from general limitations of unilateral CI supply in binaural CI candidates, it has been shown that left ear placement resulted in restricted long-term language outcomes in comparison to initial right ear cochlear implantation (Geers et al. 2016).

In patients suffering from asymmetrical hearing loss, a bimodal provision can be advised with a cochlear implant on the side with profound hearing loss and a conventional hearing aid on the opposite ear (see Sect. 18.4). Recently it has been further shown that children with unilateral hearing loss benefit from cochlear implantation owing to successful binaural processing and integration of electrical and acoustic stimulation (Hassepass et al. 2013). For patients with stable low-frequency residual hearing, specific devices for electro-acoustic stimulation should be considered (see Sect. 18.7). Apart from severe-to-profound sensorineural hearing loss, cochlear implants might also be suitable in special sorts of hearing disorders such as auditory neuropathy. In the case of deafness resulting from meningitis, immediate implantation is necessary owing to the risk of cochlear fibrosis and rapid ossification, which can be assessed by MRI (see Sect. 16.​21).

For many years, the lower age limit for implantation was 1–2 years. There is increasing evidence that early implantation in children before 12 months of age provides a significant advantage for spoken language achievement (see, e.g. Nicholas and Geers 2013). However, such a treatment modality should be decided cautiously and only after obtaining valid and stable objective and subjective hearing thresholds especially in children with high potential of recovery of an abnormal ABR (Psarommatis et al. 2011).

Apart from the challenges in diagnosis and anaesthetic and surgical management, a cochlear implantation in these very young children requires an adequate provision of post-operative rehabilitative resources.

For deaf children who are not cochlear implant candidates owing to cochlear nerve aplasia, the auditory brainstem implant (ABI) might be a reasonable option although providing inferior speech and language outcome perspectives in comparison with CI provision (Noij et al. 2015).

18.6.5 Post-Operative (re) Habilitation and Follow-Up

Beside preoperative audiologic assessment and surgery, the post-operative (re)habilitation is a centrepiece of the three-part way of CI provision. In principle, adults with a post-lingual acquired hearing loss need a specified rehabilitation programme for restoration of hearing and speech understanding. In contrast, prelingual deafened children enter a habilitation process for the acquisition of speech and communication skills. Commonalities and differences of habilitation and rehabilitation approaches have to be considered in the therapeutic content, the structure and the duration of the different programmes.

Speech and language therapy and cochlear implant fitting represent central aspects of habilitation programmes in children. Special focus is on early intervention and therapeutic parental guidance programmes with respect to intra-familial communication skills. Further therapeutic issues include principles of linguistic enrichment, augmentative communication and literacy training in the hearing-disabled children. It encourages training in respect of specific deficits, i.e. training of compensatory strategies, and might include alternative modes of communication. However, rehabilitation programmes are not limited to speech therapy and fitting but require a holistic approach to coordinate a multidisciplinary collaboration. Among others, this includes the management of psychological and socio-emotional sequelae for the child and its family and the consideration of educational needs. Further, because of the incidence of vestibular loss in children with cochlear implants and missing spontaneous recovery after implantation, a specific vestibular rehabilitation might be considered (Janky and Givens 2015). For a detailed description of aural rehabilitation approaches as applied after cochlear implantation, see Sect. 18.13.

The structures of (re)habilitation programmes after cochlear implantation show regional differences depending on health insurance funds, national legal regulations of special support and local developments. To provide focused clinical experience in the requested multidisciplinary programmes, they are commonly offered by specialised institutions (cochlear implant rehabilitation centres). These centres integrate the work of different professions: in particular physicians specialised in communication disorders, speech and language therapists, physicists or engineers, psychologists, occupational or music therapists and administration staff.

Generally, (re)habilitation starts with the initial fitting about 3–4 weeks after implantation. Often, speech and language therapists have already been introduced to the family owing to their counselling and diagnostic work before surgery. In prelingual deaf children, the multidisciplinary rehabilitation programme should run at least 3 years. Depending on the individual communication status and the local preconditions, the children and their families get regular appointments in the centre. However, cochlear-implanted patients require a lifelong follow-up care. Thus, also after completion of the rehabilitation programme, the patients have routine access to the specialists to check the device and to address problems associated with their handicap. In children this commonly includes educational and inclusion issues. In case of multiply handicapped children, the rehabilitative approach is particularly challenging and requires a specific individualisation and extension of the programme contents.

18.6.6 Bilateral Cochlear Implantation

Binaural hearing describes the integration of information that the brain receives from the two ears. By means of the head shadow effect and the central processing of listening cues based on timing, frequency and level between both ears, binaural hearing clearly enhances sound localisation and speech understanding in noise.

In many patients with profound hearing loss in both ears, unilateral cochlear implantation provides sufficient speech understanding in quiet. However, these unilaterally implanted patients frequently complain about difficulties in everyday listening conditions, such as impossible sound localisation, often creating a safety issue, and hearing restrictions in noise. Consequently, these patients should be considered for bilateral implantation because of the expectancy of improved speech intelligibility and sound localisation with two devices. This is supported by the psychoacoustic findings of the importance of bilateral hearing for normal-hearing people and hearing aid recipients.

Bilateral implantation can be undertaken either simultaneously or sequentially. Simultaneous surgery of both implants during one operation is commonly performed in children with bilateral deafness. Sequential surgery means a patient initially receives one implant and then later on decides to have the other ear implanted as often experienced in patients with progressive hearing loss.

Recently, a European Bilateral Pediatric Cochlear Implant Forum consensus statement was published: “Currently we feel that the infant or child with unambiguous cochlear implant candidacy should receive bilateral cochlear implants simultaneously as soon as possible after definitive diagnosis of deafness to permit optimal auditory development; an atraumatic surgical technique designed to preserve cochlear function, minimise cochlear damage, and allow easy, possibly repeated re-implantation is recommended” (Ramsden et al. 2012).

In patients with asymmetrical hearing loss and adequate residual hearing on the better side, a bimodal supply should be advised with a CI on the side with profound hearing loss and a conventional hearing aid on the opposite ear (see Sect. 18.4).

18.7.1 Electric-Acoustic Stimulation (EAS): Basic Principles

Traditionally, cochlear implants (CI) have been provided to children who have severe-to-profound sensorineural hearing loss. More recently, owing to better sound processing techniques, advances in technology and improved hearing preservation (HP) surgery, children with functional low-frequency hearing and severe-to-profound or even complete high-frequency hearing loss can also be considered as candidates for CI (see Fig. 18.23). Individuals with this type of hearing loss are often referred to as having “partial hearing” because they are able to hear well at low frequencies.

Partial deafness can be congenital or acquired. Kuthubutheen et al. (2012) have identified the more frequent causes of partial deafness in children as genetic variation, very low birth weight in premature babies or drug-induced hearing loss due to ototoxic antibiotic or cisplatin.

The strategy from which these children can benefit is “electric-acoustic stimulation (EAS)”, first described by von Ilberg et al. (1999). Children who are fitted with EAS are able to exploit the advantages of using both electric and acoustic stimulation in the same ear. Electric stimulation of the auditory system is transmitted via the CI (to provide audibility to the very poor high-frequency hearing at the base of the cochlea), and the acoustic stimulation is via the hearing aid in the same ear (to maintain frequency resolution and waveform fine structure to residual low-frequency hearing at the apical part of the cochlea). As depicted in Fig. 18.24a, both the CI and the hearing aid are integrated in a single behind-the-ear (BTE) sound processor. In cases where the child has normal low-frequency hearing, unamplified acoustic stimulation can occur in combination with a CI in the same ear.

In addition to a conventional cochlear implant, an acoustic stimulator is integrated in the BTE housing (see Fig. 18.24a) in order to transmit the low frequencies into the outer ear canal. The characteristic of the acoustic stimulator is depicted in Fig. 18.24b. Its maximal gain of 40–50 dB SPL is restricted to the frequency range 125–1500 Hz.

EAS is typically realised in the same ear (see Fig. 18.24a), but the combination of acoustic and electric stimulation can be clinically implemented in different modalities (see Fig. 18.25).

Ipsilateral EAS	Combined EAS speech processor in one ear
Bimodal	CI in one ear; hearing aid in the opposite ear
Bilateral EAS	Combined EAS speech processor in both ears
Binaural EAS	Combined EAS speech processor in one ear; hearing aid in the opposite ear
Electric complement	CI for high frequencies only; no amplification at low frequencies needed

The EAS combination helps to compensate for some of the deficits of CIs, such as small electrical dynamic ranges and poor temporal information. It is well documented that the amount of speech information available to children via a CI alone is quite limited (Wilson and Dorman 2008), especially in challenging and noisy environments. EAS offers a new possibility for regaining satisfactory hearing and speech perception, above and beyond what hearing aids alone can achieve, or what CIs alone can provide, in children who suffer from severe or total high-frequency hearing loss. EAS is particularly effective in situations with competing sound, especially where there are multiple talkers. It has not only an additive but in many cases a synergistic effect (Wilson and Dorman 2008).

18.7.2 Hearing Preservation

As the performance of EAS largely depends on the amount of residual acoustic low-frequency hearing, a meticulous surgical technique is necessary to minimise trauma to the delicate intra-cochlear structures. It is particularly important not to interfere with the still functioning auditory system of the apical region during the insertion of the electrode carrier.

Consequently, the insertion depth of the electrode should correspond to the amount of residual hearing: the more low-frequency hearing to be preserved, the shorter the electrode should be. However, in order to guarantee a fully functioning CI system in the rare cases of subsequent partial or complete hearing loss, the insertion depth should not fall below 22 mm. Furthermore, the individual length of the cochlear duct, which can vary considerably (Erixon et al. 2009), has to be determined preoperatively by high precision imaging. Owing to the development of softer electrodes of smaller diameter, there is now a tendency to use longer electrodes, and successfully, in hearing and structure preservation surgery. This is particularly reasonable in cases with a progressive hearing loss.

In addition to the hearing and structure preservation surgery, other factors such as pre-, intra- and post-operative steroid application (Sweeny et al. 2015) and gene therapy—as a future option (Staecker et al. 2007)—are applied to support the amount of early and long-term preservation of acoustic hearing.

Under these conditions, with the use of a 20 mm electrode array, the risk of losing residual hearing in children was assessed by Skarżyński and Lorens (2010) to be less than 15%. Comparable HP results in children have also been found with longer electrode arrays of 24 mm. Thus Rajan et al. (2012) reported an average loss of hearing in children of 3 dB (±1.2 dB standard deviation). Considering that even small amounts of acoustic hearing can be important for speech recognition, any attempt should be made to preserve it, even though a subsequent successful implementation of EAS cannot be precisely predicted.

18.7.3 Limitation of Hearing Aids with a Significant High-Frequency Hearing Loss

Children with partial hearing, i.e. severe-to-complete high-frequency hearing loss, usually wear bilateral high-power hearing aids and are often reported to be “doing well” because they are compared with other severe-to-profound hearing-impaired children. This results in a misunderstanding of the child’s hearing difficulties and an underestimation of the child’s true potential.

These children will have great difficulty perceiving speech cues associated with the manner and place of articulation, even with the best hearing aids available. The substantial loss of inner hair cells in the high-frequency region of the cochlea prevents the transmission of temporal and spectral cues to the brain (Turner et al. 2004). This will inhibit the neural coding of these speech cues that define various phonemes. The use of frequency-lowering and frequency-compression aids may result in good detection of high-frequency sounds, but the child will not be able to discriminate between them with accuracy (Gifford et al. 2007). Therefore, inadequate high-frequency amplification results in perception of sounds that lacks the quality and clarity important for word discrimination and speech understanding in noise.

Children need to be able to hear and discriminate high-frequency speech sounds in order to develop them in their own speech. Inaccurate speech patterns developed through compromised hearing may be irreversible, even with remedial intervention. Persistent inadequate access to sound can result in impaired speech intelligibility and quality, subtle language delays and vocabulary gaps that can worsen as the child gets older. Delage and Tuller (2007) observed language delays in over 50% of adolescents with prelingual mild-to-moderate hearing loss. Additionally, Yoshinaga-Itano et al. (2010) observed that a higher proportion of children with severe-to-profound hearing loss who use hearing aids are “gap openers” (i.e. the gap between their age-equivalent language scores and chronological age increases over time), compared with their matched peers with profound hearing loss and CI, who are more likely to be “gap closers” (i.e. the gap between their age-equivalent language scores and chronological age closes over time).

18.7.4 EAS Indication in Children

Apart from the given audiological limits (Fig. 18.23), specific guidelines regarding CI for children with partial hearing have yet to be established (Gratacap et al. 2015). It is therefore imperative that any EAS candidate has individual evaluation. As a consequence, professionals must understand the limitations of hearing aid technology and the potential impact these limitations have on a child’s speech and language development. Increasing awareness about the consequences of partial deafness, together with early detection and intervention, can prevent permanent speech and language impairment in these children (Jayawardena et al. 2012).

Early intervention with CI is an established principle for congenitally severe-to-profound deaf children (see Sect. 18.6). In the same way, unless there is early intervention of children with congenital partial hearing, functional outcomes will be compromised. Therefore, families should be counselled on the possibility of CI and EAS, preferably within the first year of their child’s life or diagnosis of hearing loss. They need to understand the long-term implications of high-frequency hearing loss and be reassured about HP. Waiting for their child to fail linguistically or academically is leaving the referral too late.

18.7.5 EAS Assessment Test Battery

Ascertaining the amount of benefit that a child receives from hearing aids versus the potential benefit of CI can be challenging in this client group (see Fig. 18.26 and Table 18.1). Not only does it require detailed assessment but also ongoing extensive counselling with the family. Owing to the progress in speech understanding and speech performance in the early years, parents might be of the opinion that their child is hearing adequately enough with their hearing aids. Furthermore, parents may worry that any low-frequency hearing will be irreversibly damaged during CI surgery, thereby focusing more on what the child has to lose, rather than on what the child could gain from EAS.

Table 18.1

Comparison between hearing aids and EAS showing the potential advantages (in green) versus disadvantages (in orange) of hearing aids and EAS

A complete pre-implant assessment test battery of hearing thresholds, developmentally appropriate speech perception in quiet and in noise, speech and language development, cognitive abilities, educational attainment and quality of life is required (see Fig. 18.26). It may also be necessary to repeat certain tests at specified intervals, in order to ascertain if the predicted rate of progress is being achieved with hearing aids alone.

In addition to determining hearing thresholds, functional hearing ability must be assessed, in each ear separately in quiet, to determine if there is an interaural difference. This will help in determining whether unilateral implantation (i.e. the child uses bimodal stimulation) or bilateral implantation is more appropriate. If implanted unilaterally, generally the poorer functioning ear is implanted, leaving the better ear for the hearing aid. This is contrary to traditional thinking. Speech perception tests carried out in noise are particularly important because the detrimental effects of partial hearing may only be apparent in adverse listening conditions.

Alongside pre-recorded assessments, functional speech perception tests may include aided live voice Ling sound detection and discrimination and minimal pair discrimination with particular focus on high frequencies and VCV/CVC (vowel-consonant-vowel/consonant-vowel-consonant) discrimination. If the child is preverbal, then tests of discrimination may include the auditory speech sounds evaluation (A(section)E) (Govaerts et al. 2006), which does not require the child to understand words.

Receptive and expressive language must be carefully evaluated by using standardised language assessments, and if more evidence is still required to determine whether EAS is appropriate, then the tests should be re-administered over a specified period of time to see whether the predicted amount of progress has been made. Children learn spoken language through incidental listening. Whilst it is possible for children with partial hearing to learn reasonable functional communication, they are likely to have some delays. Detailed assessment, including vocabulary and concepts if appropriate, will highlight any difficulties the child may be experiencing.

The EAS pre-implant assessment can also involve standardised cognitive tests to determine if the child is accessing enough sound to develop their speech and language properly. Comparisons between non-verbal cognitive test results with verbal cognitive test scores and language assessment scores can be made in order to see if there is a mismatch. A child not reaching his verbal potential may be indicative of compromised hearing.

Formal and informal quality of life measures, either through questionnaires or simple discussions with the family, can provide insight into peer interaction, the ability to cope in different communication situations and the child’s overall emotional contentment. Information gleaned through these discussions can also contribute to the overall picture of how the child’s hearing loss is impinging on their development.

Throughout the assessment described above, it is essential that there is ongoing feedback, discussion and counselling with parents, the child (if old enough) and the child’s team of support professionals. Some parents may need help to shift their focus to what the child has to gain from EAS, instead of being solely concerned about what they might lose. Parents therefore need to understand what each assessment is for, the results of each and the overall prognosis for their child’s speech, language and educational attainment. They are then in a position to make an informed choice on behalf of their child.

18.7.6 Results with EAS

EAS studies to date have mainly been carried out on adults. Those studies have shown that EAS can significantly improve speech perception in quiet but particularly in challenging noisy conditions. A European multicentre clinical trial was conducted by Gstoettner et al. (2008). In the best-aided condition with bilateral hearing aids, preoperative open-set sentence scores were 24% in quiet and 14% in noise. Twelve months after EAS, the speech recognition scores had significantly increased to 76% in quiet and 60% in noise. Studies in adults have also shown an improvement in music enjoyment and natural sound quality with EAS when compared with CI alone (Brockmeier et al. 2010).

In those rare cases where partial hearing cannot be primarily preserved, or when the preserved hearing deteriorates over time, it is possible to increase electrical input into the lower frequencies gradually until the EAS user has switched over to full electrical stimulation. Outcomes of partially hearing adults who lost their residual hearing post-EAS still show better results with a CI than the hearing aid that they had worn before surgery (Lorens et al. 2008). Furthermore, if reimplantation is required owing to device failure, preservation of residual hearing is possible, as described by Jayawardena et al. (2012).

There is no reason to believe that children should not benefit from EAS in the same way as adults; indeed, Skarżyński et al. (2002) published the first cases of HP surgery with EAS and “electrical component” strategies in children and found that the children performed equally well as, or even better than, comparable adult recipients.

For congenital partial hearing loss in children, early implantation for EAS yields better results in the same way as for “traditional” CI candidates (Gratacap et al. 2015). Wilson et al. (2016) found that the speech intelligibility of younger children with congenital partial hearing consistently improved after CI, but not for children who were implanted when older.

Whilst children with partial hearing may already function “well” with their hearing aids in a quiet environment, the greatest benefit is often in noise. Skarżyński and Lorens (2010) showed children’s open-set word scores in noise improved from 7% (best aided before EAS) to 47% (after EAS).

18.7.7 Summary

Children with partial hearing can gain significant benefit from EAS, particularly if they are implanted before language gaps or irreversible speech patterns become established. A growing body of research and clinical evidence is now able to show surgical success with hearing preservation techniques in children; moreover, the evidence demonstrates the significant gains that EAS has over hearing aids in challenging listening situations. Professionals working with families of children with partial hearing have a crucial role in providing information and reassurance in order to facilitate timely referrals to CI teams.

18.11.1 Introduction

Hearing aids (HA) and cochlear implants (CI) can compensate for the loudness deficit of a sensorineural hearing loss. But any such loss is not only characterised by its loudness deficit but also by a degradation of the quality of hearing with respect to the discrimination of small frequency and time differences and distortion. Furthermore, the passage of the sound through the tiny microphone and especially the tiny receiver of a hearing aid, or the limited number of channels of a CI, already provides a signal of restricted sound quality and bandwidth to the ear. In summary, even after an optimal fitting of a HA or CI, “normal hearing” cannot be restored by these devices; therefore hearing and understanding can still be very difficult and sometimes impossible, especially in noisy environments.

Further improvement is possible (and necessary) through the use of additional listening devices such as loop systems or wireless sound transmitter systems, e.g. the former FM systems (frequency modulation systems) and now digital wireless transmitter systems or Bluetooth streamers, which feed the sound signal from a remote microphone, TV set or telephone directly into the hearing aid. A classic example of using a wireless transmitter system for hearing-impaired children would be in school, where the teacher would wear a wireless microphone (Fig. 18.27), which picks up the voice of the teacher near his mouth and sends it wirelessly to a receiver that is attached to the pupil’s hearing aids (Fig. 18.28) providing the pupil with a clear speech signal of the teacher.

More and more competing and technically sophisticated systems are coming on the market, but a number of the systems work only within the range of products of one specific manufacturer and cannot be used with a hearing aid from a different manufacturer. Therefore for some of these systems, one has to see them as a combined package of the two hearing aids together with a wireless transmitter system tailored to the individual needs of the hearing-impaired (adult or adolescent) person.

Infants and children who are still learning to decode and understand speech need a higher signal-to-noise ratio for speech comprehension than that of adults with well-developed auditory systems and communication skills. Without a good positive signal-to-noise ratio, children cannot detect grammatical markers such as unvoiced word endings. Only a reliable and consistent input of these grammatical markers and all soft speech sounds allows the children to develop their grammatical knowledge and later on their phonological awareness. Depending on their degree of hearing loss and the challenges of their acoustic environment, a wireless microphone system can be necessary even for infants starting around 1 year of age.

18.11.2 Fitting, Verification and Validation of Wireless Microphone Systems

As wireless microphone systems (FM) or other assistive listening devices are often coupled to hearing aids or cochlear implants that do not come from the same manufacturer, and as these combined systems are used in a wide range of environments such as TV sound transmitters or telephone amplifiers at home; loop systems in churches, cinemas or theatres; and FM systems in schools, universities or conferences, it is not possible to take into account in the clinical test situation all the sources of interference that might influence the performance in real life. Therefore any complaint by the child should be taken seriously, and the complete system of hearing aid and assistive listening device has to be checked not only in the laboratory but also with simultaneous inputs to FM and HA to judge the overall signal quality. The relationship of the FM level to the hearing aid microphone has to be performed under the conditions of actual use of the system.

18.11.3 Special Issues

If important sounds such as alarm bells, telephones, doorbells or alarm clocks, and even the sound of a crying baby, cannot be made audible enough for the hearing-impaired person, electronic systems can transform these sound signals into a visible signal (e.g. a flashing light) or a tactile signal (e.g. a vibration). For this purpose wired and wireless alarm systems are available. Before purchasing one of these systems, testing the system is always recommended.

If speech can no longer be made audible, or to relieve the strains of difficult listening situations, it is necessary to use text or signing. SMS and Internet with email, video telephone or speech-to-text services provide a number of easily accessible communication options.

18.12.1 Room Acoustics of Classrooms

Most classrooms are designed to provide space for a maximum number of pupils whilst offering free line of sight to the lecture desk of the teacher. These conditions might be optimal for the visual aspects of “talk and chalk” teaching style but are often problematic because of the sound field distribution in classrooms.

18.12.2 Improvement of Classroom Acoustics

A number of methods can be applied to improve the acoustics in classrooms. Some of them require major changes of the room boundaries and might require costly structural modifications of walls and floors. Some are easy to implement if no such modifications are necessary. The decision on the extent and potential impact on acoustic measures can be made once the nature and intensity of the present unfavourable sound field and the envisaged improvement are defined.

18.13.1 Aural Habilitation Programmes

Deaf children today have wonderful opportunities to develop language and listening through advanced hearing aid technology. However, providing the equipment is only the start of the journey, not an end in itself. Clinicians must work closely with educators and parents to optimise the opportunities available.

It is also important that professionals provide families with unbiased information on the full range of approaches available and be skilled in supporting families to consider and make properly informed choices (Doherty-Sneddon 2003; Young et al. 2006). Each family is unique and influenced by its own complex tapestry of personal history and cultural experience. A communication approach that suits one child and family may not be right for another, and it is important for families to have access to unbiased and independent information to support them in deepening their own understanding of their potential choices (Carr 2015).

The main types of aural habilitation programmes are categorised below:

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