**5. Limitations in outcomes with unilateral cochlear implants**

Historically, the consequences of unilateral hearing loss (UHL) have been underestimated, both for children with normal hearing and those with a unilateral cochlear implant, as spoken language can still be developed with one hearing ear. Prior to the introduction of neonatal hearing screening, many children with UHL were undiagnosed until they attended school, where communication difficulties in noisy educational environments or failure to progress academically at the expected rate raised suspicions of hearing loss. Although there has been limited research on the effect of UHL on the development of spoken language, mild through to significant delays have been reported in several studies of children with UHL and normal hearing in the unimplanted ear, although there has been insufficient follow-up to determine whether the reported delays persisted through childhood (Cho Lieu, 2004). A review of the literature in this area also found that school-aged children with UHL have increased rates of academic failure (22-35% rate of repeating at least one grade), additional needs for educational assistance (12-41%), and behavioural problems in the classroom (Cho Lieu, 2004).

Despite the fact that many children with a unilateral implant demonstrate excellent speech perception abilities in the controlled testing environment of a sound proof booth (Cheng et al., 1999; Leigh et al. 2008c; Sarant et al., 2001), this performance does not represent their speech perception abilities in the real world. The difficulties experienced by children with one normal hearing ear and one ear with UHL are similar (but worse) for children with a

Cochlear Implants in Children: A Review 357

decision, as loss of functional and useful hearing is being risked for a probable, but not guaranteed, benefit. Parents usually take into account their child's degree of hearing loss in both ears (if the child has no cochlear implants) or in the non-implanted ear, professional recommendations, costs (typically between \$US40,000 -\$US60,000 (Papsin & Gordon, 2007), their own attitudes and desires for their child, and surgical/medical and other risks (see section 6.1.4). Parents of children who are deemed eligible by an implant team for bilateral cochlear implants may still choose to give their child a unilateral implant. Reasons for this decision have included a desire to see what the benefits of one implant are before proceeding with another, concerns about the appearance of children wearing two speech processors, saving an ear for future technological developments (see 6.1.3), and difficulty

**6.1.2 Physiological and functional arguments for bilateral cochlear implantation** 

The arguments for bilateral cochlear implantation include stimulation of both auditory nerves to ensure that the better ear is stimulated, as the benefits of cochlear implantation are not necessarily symmetrical for each ear. As previously discussed, many factors influence outcomes, and although some factors will be the same for both ears in a particular individual (for example, communication mode, cognitive ability etc.), others may not. These could include the anatomical structure and physiology of the ears, effects of the pathology that caused the hearing loss, and in the case of children who receive two cochlear implants separated in time (sequential implantation), the duration of deafness will differ between the ears. A further reason for bilateral cochlear implantation is to prevent the neural degeneration that has been documented in humans and animal studies as a result of auditory deprivation (Hardie, 1998; Sharma et al., 2002; Shepherd, 1997). Bilateral implantation also ensures that children still have hearing in the case of speech processor or device failure in one ear, which can significantly reduce stress for children and their families if these events occur. Finally, having bilateral cochlear implants may facilitate binaural hearing, which requires the perception of auditory information in both ears. As discussed earlier, children with unilateral cochlear implants experience the difficulties associated with unilateral deafness, such as an inability to localize sounds, and difficulty perceiving speech in background noise. For the relatively small number of children who have sufficient hearing to use a hearing aid in their non-implanted (or contralateral) ear, the literature shows that binaural benefit is gained through use of the cochlear implant and hearing aid together (Frush Holt et al., 2005; Mok et al., 2007). However, for many children with a bilateral profound or severe-profound hearing loss, the use of a contralateral hearing aid in the non-implanted ear is not a viable option, due to a lack of residual hearing. For these children, bilateral cochlear implantation is the only means of providing binaural hearing.

Arguments against bilateral implantation include 'saving' an ear for future technology while using a hearing aid with residual hearing (if there is sufficient residual hearing). Although it is known that changes in the cochlea occur after implantation, and that these are permanent, it is not known whether repeated re-implantation with cochlear implants or with other future technology is possible after many years of cochlear implant use (although reimplantation is usually successful in the case of device failure). It is also unknown if or

accepting children's hearing loss.

**6.1.3 Access to future technology** 

single cochlear implant and a severe-profound or profound hearing loss in the nonimplanted ear. These include difficulty understanding speech that is soft, or speech in noisy environments, such as the playground or classroom, and difficulty locating sound sources, such as their peers in a group conversation, or their teachers in the classroom. These auditory challenges can limit their ability to follow or take part in a group conversation, or to focus in the correct direction when the teacher begins to speak. The amount and quality of speech heard by children with one cochlear implant and a significant hearing loss in the other ear is greatly reduced and fragmented compared to what is heard by children with normal hearing. Further, understanding what they do hear is made difficult by their often delayed language skills. With poor language knowledge, many of these children are unable to piece together poorly heard or overheard information, and therefore to learn incidentally (without direct teaching), as do children with normal hearing. The inability to 'overhear' spoken conversations limits the access of these children to many avenues of incidental learning, and therefore restricts their acquisition of knowledge of language, social interaction, and how the world works, stifling their development in many areas.

A unilateral cochlear implant does not guarantee the development of language, speech production, academic or social skills comparable to those of children with normal hearing. Although there are many children with a unilateral cochlear implant who are able to develop these skills at an age-appropriate rate, there also remain many who show delayed development in these areas, some of whom maintain or increase their delay through to adulthood. Given the difficulties of unilateral hearing loss, giving children bilateral cochlear implants could potentially improve outcomes.

### **6. Bilateral cochlear implants**

A recent report on worldwide trends in bilateral cochlear implantation estimated that 59%of bilateral cochlear implant recipients in the U.S., and 78% of recipients in other countries are currently children (Peters et al., 2010). It was observed that by the end of 2007, 70% of all bilateral cochlear implants had been received by children, with children aged 3-10 years being most highly represented in this group (33% of all bilateral surgeries; Peters et al., 2010). 70% of children received 2 cochlear implants in sequential operations (2 separate operations). Of the remaining 30%, children aged less than 3 years were the only group for whom the majority (58%) received bilateral cochlear implants simultaneously (during the same operation). Bilateral cochlear implantation in children is a growing trend worldwide; in 2010, implant manufacturers' databases indicated that there were 4986 children with bilateral implants (Peters et al., 2010).

#### **6.1**

#### **6.1.1 Decision making**

The decision to give a child one or two cochlear implants is a difficult one for parents, despite the growing trend toward implanting children at a young age with simultaneous bilateral cochlear implants. Until recently, there has been a lack of strong evidence to support bilateral implantation, particularly with regard to longer term outcomes (Hyde et al., 2010). For parents of children with no useable residual hearing, the decision is more straightforward, as binaural hearing offers significant benefits over monaural hearing. However, parents of children with useable aided residual hearing face a more difficult

single cochlear implant and a severe-profound or profound hearing loss in the nonimplanted ear. These include difficulty understanding speech that is soft, or speech in noisy environments, such as the playground or classroom, and difficulty locating sound sources, such as their peers in a group conversation, or their teachers in the classroom. These auditory challenges can limit their ability to follow or take part in a group conversation, or to focus in the correct direction when the teacher begins to speak. The amount and quality of speech heard by children with one cochlear implant and a significant hearing loss in the other ear is greatly reduced and fragmented compared to what is heard by children with normal hearing. Further, understanding what they do hear is made difficult by their often delayed language skills. With poor language knowledge, many of these children are unable to piece together poorly heard or overheard information, and therefore to learn incidentally (without direct teaching), as do children with normal hearing. The inability to 'overhear' spoken conversations limits the access of these children to many avenues of incidental learning, and therefore restricts their acquisition of knowledge of language, social

interaction, and how the world works, stifling their development in many areas.

implants could potentially improve outcomes.

**6. Bilateral cochlear implants** 

bilateral implants (Peters et al., 2010).

**6.1.1 Decision making** 

**6.1** 

A unilateral cochlear implant does not guarantee the development of language, speech production, academic or social skills comparable to those of children with normal hearing. Although there are many children with a unilateral cochlear implant who are able to develop these skills at an age-appropriate rate, there also remain many who show delayed development in these areas, some of whom maintain or increase their delay through to adulthood. Given the difficulties of unilateral hearing loss, giving children bilateral cochlear

A recent report on worldwide trends in bilateral cochlear implantation estimated that 59%of bilateral cochlear implant recipients in the U.S., and 78% of recipients in other countries are currently children (Peters et al., 2010). It was observed that by the end of 2007, 70% of all bilateral cochlear implants had been received by children, with children aged 3-10 years being most highly represented in this group (33% of all bilateral surgeries; Peters et al., 2010). 70% of children received 2 cochlear implants in sequential operations (2 separate operations). Of the remaining 30%, children aged less than 3 years were the only group for whom the majority (58%) received bilateral cochlear implants simultaneously (during the same operation). Bilateral cochlear implantation in children is a growing trend worldwide; in 2010, implant manufacturers' databases indicated that there were 4986 children with

The decision to give a child one or two cochlear implants is a difficult one for parents, despite the growing trend toward implanting children at a young age with simultaneous bilateral cochlear implants. Until recently, there has been a lack of strong evidence to support bilateral implantation, particularly with regard to longer term outcomes (Hyde et al., 2010). For parents of children with no useable residual hearing, the decision is more straightforward, as binaural hearing offers significant benefits over monaural hearing. However, parents of children with useable aided residual hearing face a more difficult decision, as loss of functional and useful hearing is being risked for a probable, but not guaranteed, benefit. Parents usually take into account their child's degree of hearing loss in both ears (if the child has no cochlear implants) or in the non-implanted ear, professional recommendations, costs (typically between \$US40,000 -\$US60,000 (Papsin & Gordon, 2007), their own attitudes and desires for their child, and surgical/medical and other risks (see section 6.1.4). Parents of children who are deemed eligible by an implant team for bilateral cochlear implants may still choose to give their child a unilateral implant. Reasons for this decision have included a desire to see what the benefits of one implant are before proceeding with another, concerns about the appearance of children wearing two speech processors, saving an ear for future technological developments (see 6.1.3), and difficulty accepting children's hearing loss.

#### **6.1.2 Physiological and functional arguments for bilateral cochlear implantation**

The arguments for bilateral cochlear implantation include stimulation of both auditory nerves to ensure that the better ear is stimulated, as the benefits of cochlear implantation are not necessarily symmetrical for each ear. As previously discussed, many factors influence outcomes, and although some factors will be the same for both ears in a particular individual (for example, communication mode, cognitive ability etc.), others may not. These could include the anatomical structure and physiology of the ears, effects of the pathology that caused the hearing loss, and in the case of children who receive two cochlear implants separated in time (sequential implantation), the duration of deafness will differ between the ears. A further reason for bilateral cochlear implantation is to prevent the neural degeneration that has been documented in humans and animal studies as a result of auditory deprivation (Hardie, 1998; Sharma et al., 2002; Shepherd, 1997). Bilateral implantation also ensures that children still have hearing in the case of speech processor or device failure in one ear, which can significantly reduce stress for children and their families if these events occur. Finally, having bilateral cochlear implants may facilitate binaural hearing, which requires the perception of auditory information in both ears. As discussed earlier, children with unilateral cochlear implants experience the difficulties associated with unilateral deafness, such as an inability to localize sounds, and difficulty perceiving speech in background noise. For the relatively small number of children who have sufficient hearing to use a hearing aid in their non-implanted (or contralateral) ear, the literature shows that binaural benefit is gained through use of the cochlear implant and hearing aid together (Frush Holt et al., 2005; Mok et al., 2007). However, for many children with a bilateral profound or severe-profound hearing loss, the use of a contralateral hearing aid in the non-implanted ear is not a viable option, due to a lack of residual hearing. For these children, bilateral cochlear implantation is the only means of providing binaural hearing.

#### **6.1.3 Access to future technology**

Arguments against bilateral implantation include 'saving' an ear for future technology while using a hearing aid with residual hearing (if there is sufficient residual hearing). Although it is known that changes in the cochlea occur after implantation, and that these are permanent, it is not known whether repeated re-implantation with cochlear implants or with other future technology is possible after many years of cochlear implant use (although reimplantation is usually successful in the case of device failure). It is also unknown if or

Cochlear Implants in Children: A Review 359

than, the original implants, but the risks, costs, and inconvenience of surgery must be undertaken. Another longer-term risk is the increased risk of bacterial meningitis, due to the fact that the cochlear implant is a foreign body, and can act as a nidus for infection when there is a bacterial illness (ASHA, 2004). This risk is highest for children with malformed cochleae, those who contract meningitis prior to cochlear implantation, children aged less than five years, and children with otitis media or immunodeficiency. A further longer-term complication is facial nerve stimulation, which can occur at any time after cochlear implantation, but is rare. Children most at risk of this are those with malformed cochleae. Fortunately, it is a simple procedure for an audiologist to switch off the electrode/s causing

A final and important risk that is unique to sequential bilateral cochlear implantation is that some (usually older) children may not like the sound of their second cochlear implant, and will eventually become non-users. While many children, particularly those who have had one cochlear implant and have another after a significant period of time, may not initially like the sound of their second implant, most adapt to it over time with encouragement and support. However, some children never adapt, and show a pattern of inconsistent use over several years that culminates in rejection when they are older. There have been no reports in the literature to date about adaptation and non-user rates for either large groups of children with bilateral implants or for simultaneously implanted children. Factors thought to contribute to this outcome in children with a unilateral cochlear implant include older age at implantation, dislike of the auditory percept, facial nerve pain or twitching, peer pressure in secondary school, family issues, non-mainstream school settings, use of signed communication, lack of involvement in the decision-making process (older children), and poor speech intelligibility after several years of cochlear implant use (Archbold et al., 2009;

Published information on the current non-user rate for children with unilateral cochlear implants suggests the risk of rejection is low; the reported non-user rate is currently around 3% (Archbold et al. 2009; Uziel et al. 2007). However, for children receiving a second, sequential cochlear implant, the situation is entirely different, as they must adapt to a second, different sound percept; one that may not compare favourably with that provided by their first cochlear implant. In the first study to be published on adaptation in children with bilateral implants, Galvin and Hughes (in press) noted that a higher proportion of children who were implanted simultaneously adapted to full-time use of their devices (95%) than those implanted sequentially (70%), and that adaptation to bilateral implant use was not easy for almost 20% of the 46 children studied. Both Galvin and colleagues, and Archbold (2009; in a study of long term use of unilateral cochlear implants in children) noted that children who eventually become non-users often first demonstrate a pattern of inconsistent use. Archbold also noted that children who became non-users usually had disabilities additional to their hearing loss. The possibility of this eventuality should be taken into account by parents, and also by children old enough to participate in the

When a person with normal hearing listens with two ears (rather than just one) sound quality is improved, it is easier to locate the source of a sound, and it is easier to understand

the unwanted sensation.

Ray et al., 2006; Watson & Gregory, 2005).

decision-making process.

**6.2 Benefits of bilateral cochlear implants** 

when future technologies such as gene therapy or neural regeneration will become available for clinical use, and it is accepted that there is a critical time period for central auditory brain and language development, beyond which future technology may not be beneficial. Without knowing what form future technologies may take, it is not possible to predict how useful they may be for individuals who have 'waited' and not proceeded with the current cochlear implant technology.

#### **6.1.4 Risks**

Many parents have concerns about the risks of cochlear implant surgery, and some of these risks are increased with two separate implant operations, as is the case with sequential implant procedures. Simultaneous implant operations require less than double the surgery time and eliminate the need for, and risks of, two anaesthetics and recovery periods. Complications as a result of cochlear implant surgery can be categorised as major and minor, and most occur very close to the time of surgery, although some have been reported up to 14 years post-surgery, and can recur. Major complications include infections or skin flap breakdown in the area around the implant, extrusion of the end of the electrode array outside the cochlea, device failure (requiring explantation of the device), cholesteatoma, permanent facial nerve damage, persistent eardrum perforation, cerebrospinal fluid leak with subsequent meningitis, and magnet displacement. For children with anatomical deformities of the cochlea (such as Mondini deformity, in which there are less than the normal two and a half turns in the cochlea), the risk of facial nerve damage is greater. However, reported major complication rates are very low, ranging from 2 - 5% (Bhatia et al., 2004; Cohen et al., 1989; Loundon et al., 2010).

Minor complications are those which can be resolved without surgery, and include vertigo with or without nausea, persistent otitis media (middle ear infection), facial palsy, tinnitus, mild skin flap infection, flap swelling, hematoma (bruising), taste disturbance, and pain around the operation site. The incidence of minor complications is higher and more subject to variation between cochlear implant centers; studies of large numbers of patients ranging from 4% - 20% (Bhatia et al., 2004; Dutt et al., 2005; Loundon et al., 2010). Other risks include those of any surgical procedure, including the risks associated with an anaesthetic and blood loss. Some risks are increased for younger children, including an increased risk of anaesthetic complications. A further risk is due to the relatively small size of their skulls. Although their cochleae are adult-sized at birth, their small skull size increases the risk of displacement of the electrode array with subsequent significant skull growth. There is also a high prevalence of otitis media in this age group, which raises the risk of significant infection in the implant area as a result of infection spread from the middle ear. Due to these concerns, the FDA currently approves cochlear implantation in children only from the age of 2 years and older (ASHA, 2004). In summary, although there are several possible complications of cochlear implant surgery, the incidence of life-threatening complications is extremely low, and the rates of major and minor post-operative complications are also low, making cochlear implant surgery in children a reliable and safe procedure.

Longer term risks of cochlear implantation include device failure. Although cochlear implants are designed to last for a lifetime, about 2% of devices do fail (ASHA, 2004). Device failure can result in a changed auditory percept or a total lack of function, and reimplantation is the only solution. Fortunately, most re-implants function as well as, or better

when future technologies such as gene therapy or neural regeneration will become available for clinical use, and it is accepted that there is a critical time period for central auditory brain and language development, beyond which future technology may not be beneficial. Without knowing what form future technologies may take, it is not possible to predict how useful they may be for individuals who have 'waited' and not proceeded with the current cochlear

Many parents have concerns about the risks of cochlear implant surgery, and some of these risks are increased with two separate implant operations, as is the case with sequential implant procedures. Simultaneous implant operations require less than double the surgery time and eliminate the need for, and risks of, two anaesthetics and recovery periods. Complications as a result of cochlear implant surgery can be categorised as major and minor, and most occur very close to the time of surgery, although some have been reported up to 14 years post-surgery, and can recur. Major complications include infections or skin flap breakdown in the area around the implant, extrusion of the end of the electrode array outside the cochlea, device failure (requiring explantation of the device), cholesteatoma, permanent facial nerve damage, persistent eardrum perforation, cerebrospinal fluid leak with subsequent meningitis, and magnet displacement. For children with anatomical deformities of the cochlea (such as Mondini deformity, in which there are less than the normal two and a half turns in the cochlea), the risk of facial nerve damage is greater. However, reported major complication rates are very low, ranging from 2 - 5% (Bhatia et al.,

Minor complications are those which can be resolved without surgery, and include vertigo with or without nausea, persistent otitis media (middle ear infection), facial palsy, tinnitus, mild skin flap infection, flap swelling, hematoma (bruising), taste disturbance, and pain around the operation site. The incidence of minor complications is higher and more subject to variation between cochlear implant centers; studies of large numbers of patients ranging from 4% - 20% (Bhatia et al., 2004; Dutt et al., 2005; Loundon et al., 2010). Other risks include those of any surgical procedure, including the risks associated with an anaesthetic and blood loss. Some risks are increased for younger children, including an increased risk of anaesthetic complications. A further risk is due to the relatively small size of their skulls. Although their cochleae are adult-sized at birth, their small skull size increases the risk of displacement of the electrode array with subsequent significant skull growth. There is also a high prevalence of otitis media in this age group, which raises the risk of significant infection in the implant area as a result of infection spread from the middle ear. Due to these concerns, the FDA currently approves cochlear implantation in children only from the age of 2 years and older (ASHA, 2004). In summary, although there are several possible complications of cochlear implant surgery, the incidence of life-threatening complications is extremely low, and the rates of major and minor post-operative complications are also low,

making cochlear implant surgery in children a reliable and safe procedure.

Longer term risks of cochlear implantation include device failure. Although cochlear implants are designed to last for a lifetime, about 2% of devices do fail (ASHA, 2004). Device failure can result in a changed auditory percept or a total lack of function, and reimplantation is the only solution. Fortunately, most re-implants function as well as, or better

implant technology.

2004; Cohen et al., 1989; Loundon et al., 2010).

**6.1.4 Risks** 

than, the original implants, but the risks, costs, and inconvenience of surgery must be undertaken. Another longer-term risk is the increased risk of bacterial meningitis, due to the fact that the cochlear implant is a foreign body, and can act as a nidus for infection when there is a bacterial illness (ASHA, 2004). This risk is highest for children with malformed cochleae, those who contract meningitis prior to cochlear implantation, children aged less than five years, and children with otitis media or immunodeficiency. A further longer-term complication is facial nerve stimulation, which can occur at any time after cochlear implantation, but is rare. Children most at risk of this are those with malformed cochleae. Fortunately, it is a simple procedure for an audiologist to switch off the electrode/s causing the unwanted sensation.

A final and important risk that is unique to sequential bilateral cochlear implantation is that some (usually older) children may not like the sound of their second cochlear implant, and will eventually become non-users. While many children, particularly those who have had one cochlear implant and have another after a significant period of time, may not initially like the sound of their second implant, most adapt to it over time with encouragement and support. However, some children never adapt, and show a pattern of inconsistent use over several years that culminates in rejection when they are older. There have been no reports in the literature to date about adaptation and non-user rates for either large groups of children with bilateral implants or for simultaneously implanted children. Factors thought to contribute to this outcome in children with a unilateral cochlear implant include older age at implantation, dislike of the auditory percept, facial nerve pain or twitching, peer pressure in secondary school, family issues, non-mainstream school settings, use of signed communication, lack of involvement in the decision-making process (older children), and poor speech intelligibility after several years of cochlear implant use (Archbold et al., 2009; Ray et al., 2006; Watson & Gregory, 2005).

Published information on the current non-user rate for children with unilateral cochlear implants suggests the risk of rejection is low; the reported non-user rate is currently around 3% (Archbold et al. 2009; Uziel et al. 2007). However, for children receiving a second, sequential cochlear implant, the situation is entirely different, as they must adapt to a second, different sound percept; one that may not compare favourably with that provided by their first cochlear implant. In the first study to be published on adaptation in children with bilateral implants, Galvin and Hughes (in press) noted that a higher proportion of children who were implanted simultaneously adapted to full-time use of their devices (95%) than those implanted sequentially (70%), and that adaptation to bilateral implant use was not easy for almost 20% of the 46 children studied. Both Galvin and colleagues, and Archbold (2009; in a study of long term use of unilateral cochlear implants in children) noted that children who eventually become non-users often first demonstrate a pattern of inconsistent use. Archbold also noted that children who became non-users usually had disabilities additional to their hearing loss. The possibility of this eventuality should be taken into account by parents, and also by children old enough to participate in the decision-making process.

## **6.2 Benefits of bilateral cochlear implants**

When a person with normal hearing listens with two ears (rather than just one) sound quality is improved, it is easier to locate the source of a sound, and it is easier to understand

Cochlear Implants in Children: A Review 361

2010). Other children are more limited in their localization ability; able to lateralize sounds from the left or right side of their heads confidently and with high accuracy, but unable to determine the direction of the sound source (as occurs with true binaural processing) as the stimulus is presented closer to the front and centre of their heads (Galvin et al., 2008b; Grieco-Calub & Litovsky, 2010). Many other bilaterally implanted children (particularly older children) have shown no ability at all to locate sound sources (Galvin et al., 2007a). Of the children who show some spatial awareness, many do not differ significantly in their ability to children with bimodal stimulation (a cochlear implant plus hearing aid), and none have the abilities of children with normal hearing (Sparreboom et al., 2010). Although overall the best performers are younger, not all young children demonstrate an ability to

Most of the research on outcomes for children with bilateral cochlear implants has focused on speech perception in noise and sound localization abilities. There is little research to date comparing broader outcomes of children with unilateral versus bilateral cochlear implants, and at the time of writing, there were no reports of speech production or academic outcomes. An initial theoretical analysis of the cost effectiveness of bilateral implantation suggested that it "is possibly a cost-effective use of resources", but that further data on the costs and benefits of bilateral implantation compared with unilateral implantation are required to reach a definitive conclusion (Summerfield et al., 2010). To date, two studies using standardized quality-of-life measures have attempted to determine whether bilateral implants facilitate improved quality of life in children, however neither reported a significant improvement for children with bilateral implants (Beijen, 2007; Lovett et al.,

Information on the impact of bilateral cochlear implantation on language is currently limited. A recent study comparing the preverbal communication of children implanted before age 3 years (27 bilaterally; 42 unilaterally) reported that children with bilateral cochlear implants were significantly more likely to use vocalisation to communicate and to use hearing when interacting with an adult than were children with unilateral implants (Tait et al., 2010). After statistically controlling for the influence of age at implantation and length of deafness, it was found that bilateral implantation contributed to 51% of the variance in outcomes. A multi-center study of 91 children with unilateral (n=60) and bilateral (n=31) implants reported that bilateral implantation was not associated with improved expressive or receptive language development (Niparko et al., 2010). Similarly, Nittrouer & Chappman (2009) examined the vocabulary, receptive and expressive language abilities of 58 children tested at age 3.5 years and also found no differences in outcomes between 15 children with unilateral and 26 with bilateral cochlear implants. Both of these studies provide no support, in terms of language development, for providing young children with bilateral cochlear

However, recent initial results of another prospective, multicentre study comparing outcomes for children with unilateral and bilateral cochlear implants showed a significant advantage for bilaterally implanted children with regard to language development (Sarant et al., in press). The groups of unilaterally (n= 11) and bilaterally (n=17) implanted 5-yearold children in this study did not differ with regard to average non-verbal cognitive ability,

locate sound sources (Galvin et al., 2010; Galvin et al., 2007a).

**6.2.3 Broader outcomes of bilateral implantation** 

2010).

implants.

speech, particularly in background noise. The improved sound quality with two ears is commonly described as fuller, more spacious, and more natural. To locate sound sources, the listener primarily uses the differences in timing and level of sound arriving at each ear, with sound arriving later and being softer at the ear furthest from the sound source. This localization ability allows the listener to locate sounds in the environment, to find the speaker in a group conversation, and to be more aware of changes in their auditory environment. Speech perception is improved with two ears because the brain has two opportunities to process the same signal (binaural redundancy), and because the combined signal is slightly louder (binaural summation). The benefits of two ears are particularly significant when speech and noise are coming from different directions. Firstly, due to the physical barrier of the head (the head-shadow effect), the noise level will be lower at the ear that is furthest from the noise source. Given that speech will usually be arriving from in front of the head, the level of the speech signal is equal at both ears. The listener is therefore better able to perceive speech by attending primarily to the ear at which the noise level is lower. Secondly, with speech and noise coming from different directions, each ear receives a different balance of speech and noise. The brain is able to compare these two different signals and reduce the impact of the noise to increase the salience of the speech signal (binaural unmasking).

#### **6.2.1 Speech perception**

The speech perception abilities of children with bilateral cochlear implants have been explored using both standardized measures and a variety of study-specific measures in quiet conditions and in various noise conditions (for example, Galvin et al., 2007a, b; Scherf et al., 2007; van Deun et al., 2010). A review of the research found that 11/13 of the studies reported significant improvement in children's speech perception in noise abilities (Johnston et al., 2009). Some of these improvements were due simply to the head shadow effect, or to the ability to concentrate on the sound from one ear over another (Galvin et al., 2008a; Galvin et al., 2007a; Litovsky et al., 2006a). A recent study found that although they did not perform as well as children with normal hearing, bilaterally implanted children performed significantly better than unilaterally implanted children on tests of speech perception performance in noise (Lovett et al., 2010). As with outcomes for children with unilateral cochlear implants, the degree of improvement varies widely between individuals. Improved speech perception in noise has been associated with shorter periods of hearing loss in the second ear in some studies (Litovsky et al., 2004; Peters et al., 2007; Steffens et al., 2008), but not all have found this link (Kuhn-Inacker et al., 2004; Litovsky et al., 2006a; Wolfe et al., 2007). Two studies that did not find improvements in speech perception in noise included children who had a long time period between their first and second cochlear implants. There have also been reports of improved speech perception performance in quiet conditions with bilateral implants (Scherf et al., 2007; Zeitler et al., 2008).

#### **6.2.2 Localization of sound**

Bilateral cochlear implantation has not yet shown a clear benefit for sound localization. In assessments of localization performance for long-term users to date, some children can localize sounds well (Litovsky et al., 2006b; Lovett et al., 2010). Bilateral implantation has been associated with increases of 18.5% in the accuracy of sound localization (Lovett et al.,

speech, particularly in background noise. The improved sound quality with two ears is commonly described as fuller, more spacious, and more natural. To locate sound sources, the listener primarily uses the differences in timing and level of sound arriving at each ear, with sound arriving later and being softer at the ear furthest from the sound source. This localization ability allows the listener to locate sounds in the environment, to find the speaker in a group conversation, and to be more aware of changes in their auditory environment. Speech perception is improved with two ears because the brain has two opportunities to process the same signal (binaural redundancy), and because the combined signal is slightly louder (binaural summation). The benefits of two ears are particularly significant when speech and noise are coming from different directions. Firstly, due to the physical barrier of the head (the head-shadow effect), the noise level will be lower at the ear that is furthest from the noise source. Given that speech will usually be arriving from in front of the head, the level of the speech signal is equal at both ears. The listener is therefore better able to perceive speech by attending primarily to the ear at which the noise level is lower. Secondly, with speech and noise coming from different directions, each ear receives a different balance of speech and noise. The brain is able to compare these two different signals and reduce the impact of the noise to increase the salience of the speech signal

The speech perception abilities of children with bilateral cochlear implants have been explored using both standardized measures and a variety of study-specific measures in quiet conditions and in various noise conditions (for example, Galvin et al., 2007a, b; Scherf et al., 2007; van Deun et al., 2010). A review of the research found that 11/13 of the studies reported significant improvement in children's speech perception in noise abilities (Johnston et al., 2009). Some of these improvements were due simply to the head shadow effect, or to the ability to concentrate on the sound from one ear over another (Galvin et al., 2008a; Galvin et al., 2007a; Litovsky et al., 2006a). A recent study found that although they did not perform as well as children with normal hearing, bilaterally implanted children performed significantly better than unilaterally implanted children on tests of speech perception performance in noise (Lovett et al., 2010). As with outcomes for children with unilateral cochlear implants, the degree of improvement varies widely between individuals. Improved speech perception in noise has been associated with shorter periods of hearing loss in the second ear in some studies (Litovsky et al., 2004; Peters et al., 2007; Steffens et al., 2008), but not all have found this link (Kuhn-Inacker et al., 2004; Litovsky et al., 2006a; Wolfe et al., 2007). Two studies that did not find improvements in speech perception in noise included children who had a long time period between their first and second cochlear implants. There have also been reports of improved speech perception performance in quiet conditions with

Bilateral cochlear implantation has not yet shown a clear benefit for sound localization. In assessments of localization performance for long-term users to date, some children can localize sounds well (Litovsky et al., 2006b; Lovett et al., 2010). Bilateral implantation has been associated with increases of 18.5% in the accuracy of sound localization (Lovett et al.,

(binaural unmasking).

**6.2.1 Speech perception** 

**6.2.2 Localization of sound** 

bilateral implants (Scherf et al., 2007; Zeitler et al., 2008).

2010). Other children are more limited in their localization ability; able to lateralize sounds from the left or right side of their heads confidently and with high accuracy, but unable to determine the direction of the sound source (as occurs with true binaural processing) as the stimulus is presented closer to the front and centre of their heads (Galvin et al., 2008b; Grieco-Calub & Litovsky, 2010). Many other bilaterally implanted children (particularly older children) have shown no ability at all to locate sound sources (Galvin et al., 2007a). Of the children who show some spatial awareness, many do not differ significantly in their ability to children with bimodal stimulation (a cochlear implant plus hearing aid), and none have the abilities of children with normal hearing (Sparreboom et al., 2010). Although overall the best performers are younger, not all young children demonstrate an ability to locate sound sources (Galvin et al., 2010; Galvin et al., 2007a).
