**4.1 Age at diagnosis**

With the establishment of newborn hearing screening in many developed countries around the world, the average age of diagnosis of hearing loss in these countries has dropped to 12- 25 months, with many babies identified as young as 3 months of age (Dalzell et al., 2000; Harrison et al., 2003; Watkin et al., 2007). As mentioned previously, the earlier identification of hearing loss has resulted in a rapid rise in the numbers of children receiving cochlear implants at younger ages (ASHA, 2004). It was estimated that the number of children receiving cochlear implants before the age of 2 years between 1991 and 2002 increased forty fold (Drinkwater, 2004), and it is likely that this growth rate has not declined. However, there are still many children in developed countries who are not receiving cochlear implants early in life. It is disappointing to note that despite earlier identification of hearing loss through newborn hearing screening programs, many families (and almost half of the families in the U.S. who are referred for further hearing assessment of their newborn babies) still do not receive early intervention services by the age of 6 months, as is recommended by the 2007 Position Statement of the Joint Committee on Infant Hearing (JCIH, 2007). The

al., 2007).

Cochlear Implants in Children: A Review 351

stimulation there is a period of about 3.5 years during which the central auditory system retains its maximum plasticity. This can extend in some children up to the age of approximately 7 years, after which it is significantly reduced (Sharma et al., 2005; Sharma et al., 2002). Harrison and colleagues (2005), who examined the speech perception performance of children implanted at different ages, argue that the situation is not quite as simple as this. They hypothesize that although central auditory plasticity is limited for children implanted at older ages, there is no age at which there is a clear cut-off, but instead there is an agerelated plasticity effect that depends to some extent on the tests used to assess performance. Early research on cochlear implantation in children supported the biological plasticity theory, showing a strong negative relationship between duration of deafness (or age at implant) and speech perception outcomes (Apuzzo, 1995; Nikolopoulos et al., 1999; Osberger, 1991; Staller et al., 1991). Initially, speech perception results for children who were not congenitally deaf, received their cochlear implant relatively quickly, and therefore had a shorter period of deafness, were superior to those for children with congenital deafness and later implantation (Pisoni et al., 1999; Staller et al., 1991). As Marshark (2007) noted, children who have later onset hearing loss have usually developed better language skills prior to implantation, and therefore show better achievement afterwards (for example, Moog & Geers, 2003). For children with congenital deafness, a significant correlation between age at implantation and outcomes has also been documented in many recent studies. Children implanted earlier show faster growth of speech perception (Tajudeen et al., 2010; Uziel et al., 2007), language (Connor et al., 2000; Nikolopoulos et al., 2004; Schorr et al., 2008; Tomblin et al., 2005) and reading abilities (Archbold et al., 2008a; Geers et al., 2008; James et al., 2008; Johnson & Goswami, 2010), and also have improved psychosocial outcomes (Schorr, 2006). Development of speech production is also associated with age at implantation, with slower rates of development shown by children who received their implants later (Flipsen, 2008; Peng et al., 2004; Tye-Murray et al., 1995). Interestingly, for children implanted very early, early age at implantation and speech production have been observed to have the opposite association, with one study documenting slower vocal development for children implanted when younger. Greater physical, cognitive, and social maturity were thought to provide children implanted at older ages with an advantage for early speech development (Ertmer et

More recently, there have been reports of even better outcomes in children implanted around the age of 2 years or younger, with higher proportions of children achieving speech perception, language and reading skills commensurate with those of their hearing peers (Duchesne et al., 2009; Geers, 2004; Niparko et al,. 2010; Svirsky et al., 2004). These results have been observed to be "consistent with the existence of a 'sensitive period' for language development, and a gradual decline in language acquisition skills as a function of age" (Svirsky et al., 2004). Svirsky and colleagues qualify this observation by suggesting that the auditory information provided by a cochlear implant is significantly inferior to that received by children with normal hearing, and that it is possible that sensitive periods for speech and language development may exist for cochlear implant users and not for children with

Nicholas and Geers (2007) studied the language development of 76 children who had received a cochlear implant by their third birthday. They concluded that children who received an implant by 12-16 months, before substantial spoken language delay had

normal hearing because of the diminished auditory signal the former receive.

reasons for this are varied, and include a lack of understanding of the importance of early identification and intervention, problems with follow-up systems, lack of access to appropriate services and other issues related to babies' health (Sass-Lehrer, 2011). It is also reported that around one third of pediatric implant recipients who passed the newborn hearing screening assessment subsequently become implant candidates through progressive hearing loss in the first years of life due to genetic causes such as the Connexin 26 mutation, Usher Syndrome, or to other causes such as auditory neuropathy or congenital Cytomegalovirus (CMV) (Young et al., 2011), and these children also receive cochlear implants when older.

Although age at diagnosis has been reported by many studies to be an influential factor in outcomes for children with cochlear implants, some studies have not found this link (Geers et al., 2009; Geers, 2004; Harris & Terlektsi 2011; Sarant et al., 2009; Wake et al., 2005). Two of these studies included a greater proportion of children who were diagnosed late and were therefore implanted at older ages, reporting poorer performance than other studies of children whose hearing loss was identified earlier. Nicholas and Geers (2006) reported that age at diagnosis was not a significant predictive factor in language outcomes unless it led to children receiving a cochlear implant before 24 months of age. Evidence that age at diagnosis is an important factor has become stronger as children receive cochlear implants at younger ages. Several studies have reported excellent speech perception abilities and ageappropriate language outcomes for many young children who were diagnosed with hearing loss in the first six months of life (Apuzzo, 1995; Yoshinaga-Itano, 2003b; Yoshinaga-Itano et al., 1998), and there is mounting evidence that early-diagnosed children are developing language at a faster rate than their later-diagnosed peers (Connor & Zwolan, 2004; Kennedy et al., 2006).

### **4.2 Age at implant/duration of profound deafness**

Age at implantation is often quite close to time of diagnosis early in life due to newborn screening. For children with congenital hearing loss, 'age at implant' is equal to 'duration of deafness'. Many human and animal studies of the development of the neurosensory pathways of the primary auditory cortex in the brain have suggested that the plasticity, or potential for development, of neural pathways is greatest during early development, and that there is therefore a 'critical period', during which auditory stimulation must occur in order for neural maturation to occur (Kral et al., 2001; Sharma et al., 2002). If stimulation does not occur within this timeframe, the auditory system degenerates (Kral et al., 2001; Shepherd, 1997). In humans with normal hearing, maturation of the central auditory system continues throughout childhood through to adolescence. Research with humans has shown that the central auditory system can retain its plasticity for some years without auditory input, and when stimulated by a cochlear implant will commence maturation at the same rate as for children with normal hearing, with the maturational sequence delayed by the period of sensory deprivation (Ponton et al., 1996).

It has been found, however, that after long periods of deprivation, such as in children who have used a unilateral implant for several years and have then received a second, bilateral implant, that there were abnormalities in spatial patterns of cortical activity in the brain not observed in children who received a second cochlear implant after a shorter time (Gordon et al., 2010). Further physiological studies suggest that in the absence of normal auditory

reasons for this are varied, and include a lack of understanding of the importance of early identification and intervention, problems with follow-up systems, lack of access to appropriate services and other issues related to babies' health (Sass-Lehrer, 2011). It is also reported that around one third of pediatric implant recipients who passed the newborn hearing screening assessment subsequently become implant candidates through progressive hearing loss in the first years of life due to genetic causes such as the Connexin 26 mutation, Usher Syndrome, or to other causes such as auditory neuropathy or congenital Cytomegalovirus (CMV) (Young et al., 2011), and these children also receive cochlear

Although age at diagnosis has been reported by many studies to be an influential factor in outcomes for children with cochlear implants, some studies have not found this link (Geers et al., 2009; Geers, 2004; Harris & Terlektsi 2011; Sarant et al., 2009; Wake et al., 2005). Two of these studies included a greater proportion of children who were diagnosed late and were therefore implanted at older ages, reporting poorer performance than other studies of children whose hearing loss was identified earlier. Nicholas and Geers (2006) reported that age at diagnosis was not a significant predictive factor in language outcomes unless it led to children receiving a cochlear implant before 24 months of age. Evidence that age at diagnosis is an important factor has become stronger as children receive cochlear implants at younger ages. Several studies have reported excellent speech perception abilities and ageappropriate language outcomes for many young children who were diagnosed with hearing loss in the first six months of life (Apuzzo, 1995; Yoshinaga-Itano, 2003b; Yoshinaga-Itano et al., 1998), and there is mounting evidence that early-diagnosed children are developing language at a faster rate than their later-diagnosed peers (Connor & Zwolan, 2004; Kennedy

Age at implantation is often quite close to time of diagnosis early in life due to newborn screening. For children with congenital hearing loss, 'age at implant' is equal to 'duration of deafness'. Many human and animal studies of the development of the neurosensory pathways of the primary auditory cortex in the brain have suggested that the plasticity, or potential for development, of neural pathways is greatest during early development, and that there is therefore a 'critical period', during which auditory stimulation must occur in order for neural maturation to occur (Kral et al., 2001; Sharma et al., 2002). If stimulation does not occur within this timeframe, the auditory system degenerates (Kral et al., 2001; Shepherd, 1997). In humans with normal hearing, maturation of the central auditory system continues throughout childhood through to adolescence. Research with humans has shown that the central auditory system can retain its plasticity for some years without auditory input, and when stimulated by a cochlear implant will commence maturation at the same rate as for children with normal hearing, with the maturational sequence delayed by the

It has been found, however, that after long periods of deprivation, such as in children who have used a unilateral implant for several years and have then received a second, bilateral implant, that there were abnormalities in spatial patterns of cortical activity in the brain not observed in children who received a second cochlear implant after a shorter time (Gordon et al., 2010). Further physiological studies suggest that in the absence of normal auditory

implants when older.

et al., 2006).

**4.2 Age at implant/duration of profound deafness** 

period of sensory deprivation (Ponton et al., 1996).

stimulation there is a period of about 3.5 years during which the central auditory system retains its maximum plasticity. This can extend in some children up to the age of approximately 7 years, after which it is significantly reduced (Sharma et al., 2005; Sharma et al., 2002). Harrison and colleagues (2005), who examined the speech perception performance of children implanted at different ages, argue that the situation is not quite as simple as this. They hypothesize that although central auditory plasticity is limited for children implanted at older ages, there is no age at which there is a clear cut-off, but instead there is an age-

related plasticity effect that depends to some extent on the tests used to assess performance.

Early research on cochlear implantation in children supported the biological plasticity theory, showing a strong negative relationship between duration of deafness (or age at implant) and speech perception outcomes (Apuzzo, 1995; Nikolopoulos et al., 1999; Osberger, 1991; Staller et al., 1991). Initially, speech perception results for children who were not congenitally deaf, received their cochlear implant relatively quickly, and therefore had a shorter period of deafness, were superior to those for children with congenital deafness and later implantation (Pisoni et al., 1999; Staller et al., 1991). As Marshark (2007) noted, children who have later onset hearing loss have usually developed better language skills prior to implantation, and therefore show better achievement afterwards (for example, Moog & Geers, 2003). For children with congenital deafness, a significant correlation between age at implantation and outcomes has also been documented in many recent studies. Children implanted earlier show faster growth of speech perception (Tajudeen et al., 2010; Uziel et al., 2007), language (Connor et al., 2000; Nikolopoulos et al., 2004; Schorr et al., 2008; Tomblin et al., 2005) and reading abilities (Archbold et al., 2008a; Geers et al., 2008; James et al., 2008; Johnson & Goswami, 2010), and also have improved psychosocial outcomes (Schorr, 2006). Development of speech production is also associated with age at implantation, with slower rates of development shown by children who received their implants later (Flipsen, 2008; Peng et al., 2004; Tye-Murray et al., 1995). Interestingly, for children implanted very early, early age at implantation and speech production have been observed to have the opposite association, with one study documenting slower vocal development for children implanted when younger. Greater physical, cognitive, and social maturity were thought to provide children implanted at older ages with an advantage for early speech development (Ertmer et al., 2007).

More recently, there have been reports of even better outcomes in children implanted around the age of 2 years or younger, with higher proportions of children achieving speech perception, language and reading skills commensurate with those of their hearing peers (Duchesne et al., 2009; Geers, 2004; Niparko et al,. 2010; Svirsky et al., 2004). These results have been observed to be "consistent with the existence of a 'sensitive period' for language development, and a gradual decline in language acquisition skills as a function of age" (Svirsky et al., 2004). Svirsky and colleagues qualify this observation by suggesting that the auditory information provided by a cochlear implant is significantly inferior to that received by children with normal hearing, and that it is possible that sensitive periods for speech and language development may exist for cochlear implant users and not for children with normal hearing because of the diminished auditory signal the former receive.

Nicholas and Geers (2007) studied the language development of 76 children who had received a cochlear implant by their third birthday. They concluded that children who received an implant by 12-16 months, before substantial spoken language delay had

Cochlear Implants in Children: A Review 353

have reported it to be one of the most significant factors of all those examined, having much greater influence than other variables (Geers et al., 2009; Geers, 2003). Non-verbal IQ has been shown to have a significant effect on the development of vocabulary (Mayne, 2000), language (Geers et al., 2009; Geers et al., 2008; Sarant et al., 2009; Sarant, Hughes, & Blamey, 2010), reading (Moog & Geers, 2003), and speech production (Tobey et al., 2003). Although, after adjusting for the effect of language, cognitive ability usually has no direct effect on speech perception performance, it does have an indirect effect on this outcome. This is because language is strongly influenced by cognitive ability, and is the medium through which speech perception assessments are conducted; children have to comprehend the language used in speech perception tests and respond using spoken language (Sarant et al., 2010). Many studies have demonstrated a strong association between language and speech

Cognitive delay has been associated with reduced development of speech perception and production skills in populations of children with diagnosed additional disabilities (Holt & Kirk, 2005; Pyman et al., 2000; Waltzman et al., 2000), but is also a predictive factor for children who are in the average range for non-verbal cognitive abilities (Moog & Geers, 2003). Pisoni and colleagues emphasized the importance of cognitive factors such as memory, attention, and verbal rehearsal speed in determining outcomes after implantation (Pisoni & Cleary, 2003; Pisoni et al., 1999), and postulated that 'central' cognitive factors might explain some of the previously unexplained variance in outcomes for children with cochlear implants (Pisoni & Cleary, 2003; Pisoni et al., 1999). Geers and Sedey (2011) added credence to this theory with their recent observation that faster verbal rehearsal speed contributed to better language outcomes in children implanted between 2 and 5 years of age with more than 10 years of cochlear implant experience. In further support of Pisoni and colleagues' theory, it has recently been reported that when compared to children of the same age and cognitive ability, children with cochlear implants still demonstrate language delays that are disproportionate to their cognitive potential (Meinzen-Derr et al., 2011). The cognitive processes underlying this performance-functional gap need to be investigated and understood in order to implement appropriate intervention strategies to close the gap and improve outcomes for a greater proportion of children with cochlear

Communication mode, often dichotomized into oral communication and total communication (signing plus speaking), has long been investigated as a source of variance in outcomes for children with cochlear implants, with mixed results. Proponents of oral communication maintain that maximal auditory benefit from cochlear implants can only be gained if hearing and speech are the only media for communication. There are several reports of children attending oral communication programs achieving higher speech perception and language scores than children in total communication programs (Archbold et al., 2000; El-Hakim et al., 2001; Geers et al., 2003; Meyer et al., 1998; Moog & Geers, 2003). Similarly, speech production outcomes are reported to be better for children in oral education settings. Tobey et al (2003) found oral-aural communication and teaching methods that emphasized speaking and listening to be the most influential factors in determining speech production development in children implanted by age 5 years. These

perception ability (for example, Blamey et al., 2001; Niparko et al., 2010).

implants.

**4.5 Communication mode** 

developed, were more likely to achieve age-appropriate spoken language. These children 'caught up' with their hearing peers by 4.5 years of age, whereas children implanted after 24 months of age did not. Both Nicholas and Geers (2007) and Tomblin and colleagues (2005) observed an early burst of language growth in children implanted before the age of 18 months which was not seen in children implanted after this age. More recent studies suggest implanting children as early as before 12 months of age, with strong development of speech perception and language skills reported at age-appropriate rates for many or all of the children (Svirsky et al., 2004; Tajudeen et al., 2010; Waltzman & Roland, 2005; Wie, 2010).

A review of recent studies concluded that the evidence suggests that cochlear implantation before the age of 2 years is more effective than after this time, but that it is not yet clear whether implantation of children under 12 months of age provides greater benefit (Ali & O'Connell, 2007). As implantation of children under the age of 2 years is a relatively recent practice, limited evidence has been obtained for short-term outcomes (only up to approximately 5-8 years post-implantation) and the effect of implantation at a very young age on longer-term outcomes is still unknown (Ali & O'Connell, 2007). It is also not yet known whether children implanted at older ages, who have been shown to develop more slowly, will eventually reach equivalent long-term milestones to those implanted earlier. Some more recent longer term studies support this view, showing that although age at implantation strongly influences outcomes in younger children, the effect of this factor appears to wane with increasing age and implant experience (Geers, 2004; Hay-McCutcheon et al., 2008; Moog & Geers, 2003). Finally, when considering these reports, it is also important to remember that children implanted at younger ages are more likely to use oral communication, a factor that has also been shown to improve speech perception and spoken language outcomes.

#### **4.3 Degree of hearing loss**

There is conflicting evidence regarding the influence of degree of hearing loss on outcomes for children with cochlear implants. This factor has been reported as highly predictive of outcomes for children with cochlear implants in many studies. Speech perception abilities, language development and reading in children with hearing loss and those with cochlear implants have been found to decrease with increasing severity of hearing loss (Boothroyd et al., 1991; El-Hakim et al., 2001; Holt & Svirsky, 2008; Wake et al., 2005; Zwolan et al., 1997). Nicholas and Geers (2007) observed that children with better hearing prior to implantation showed faster language growth with increasing implant experience than did children with less pre-implant hearing. Conversely, some other studies that included more children who were older when implanted and at testing have not found a significant correlation between degree of hearing loss and speech perception, vocabulary or speech production outcomes (Blamey et al. 2001a; Harris & Terlektsi, 2011). The majority of published evidence supports a significant influence of degree of hearing loss on outcomes.

#### **4.4 Cognitive ability**

Non-verbal cognitive ability has been identified as one of the most influential factors on language outcomes in preschool children with hearing loss. The influence of cognitive skills is no less important for outcomes in children with cochlear implants, and several studies

developed, were more likely to achieve age-appropriate spoken language. These children 'caught up' with their hearing peers by 4.5 years of age, whereas children implanted after 24 months of age did not. Both Nicholas and Geers (2007) and Tomblin and colleagues (2005) observed an early burst of language growth in children implanted before the age of 18 months which was not seen in children implanted after this age. More recent studies suggest implanting children as early as before 12 months of age, with strong development of speech perception and language skills reported at age-appropriate rates for many or all of the children (Svirsky et al., 2004; Tajudeen et al., 2010; Waltzman & Roland, 2005; Wie, 2010).

A review of recent studies concluded that the evidence suggests that cochlear implantation before the age of 2 years is more effective than after this time, but that it is not yet clear whether implantation of children under 12 months of age provides greater benefit (Ali & O'Connell, 2007). As implantation of children under the age of 2 years is a relatively recent practice, limited evidence has been obtained for short-term outcomes (only up to approximately 5-8 years post-implantation) and the effect of implantation at a very young age on longer-term outcomes is still unknown (Ali & O'Connell, 2007). It is also not yet known whether children implanted at older ages, who have been shown to develop more slowly, will eventually reach equivalent long-term milestones to those implanted earlier. Some more recent longer term studies support this view, showing that although age at implantation strongly influences outcomes in younger children, the effect of this factor appears to wane with increasing age and implant experience (Geers, 2004; Hay-McCutcheon et al., 2008; Moog & Geers, 2003). Finally, when considering these reports, it is also important to remember that children implanted at younger ages are more likely to use oral communication, a factor that has also been shown to improve speech perception and spoken

There is conflicting evidence regarding the influence of degree of hearing loss on outcomes for children with cochlear implants. This factor has been reported as highly predictive of outcomes for children with cochlear implants in many studies. Speech perception abilities, language development and reading in children with hearing loss and those with cochlear implants have been found to decrease with increasing severity of hearing loss (Boothroyd et al., 1991; El-Hakim et al., 2001; Holt & Svirsky, 2008; Wake et al., 2005; Zwolan et al., 1997). Nicholas and Geers (2007) observed that children with better hearing prior to implantation showed faster language growth with increasing implant experience than did children with less pre-implant hearing. Conversely, some other studies that included more children who were older when implanted and at testing have not found a significant correlation between degree of hearing loss and speech perception, vocabulary or speech production outcomes (Blamey et al. 2001a; Harris & Terlektsi, 2011). The majority of published evidence supports

Non-verbal cognitive ability has been identified as one of the most influential factors on language outcomes in preschool children with hearing loss. The influence of cognitive skills is no less important for outcomes in children with cochlear implants, and several studies

a significant influence of degree of hearing loss on outcomes.

language outcomes.

**4.4 Cognitive ability** 

**4.3 Degree of hearing loss** 

have reported it to be one of the most significant factors of all those examined, having much greater influence than other variables (Geers et al., 2009; Geers, 2003). Non-verbal IQ has been shown to have a significant effect on the development of vocabulary (Mayne, 2000), language (Geers et al., 2009; Geers et al., 2008; Sarant et al., 2009; Sarant, Hughes, & Blamey, 2010), reading (Moog & Geers, 2003), and speech production (Tobey et al., 2003). Although, after adjusting for the effect of language, cognitive ability usually has no direct effect on speech perception performance, it does have an indirect effect on this outcome. This is because language is strongly influenced by cognitive ability, and is the medium through which speech perception assessments are conducted; children have to comprehend the language used in speech perception tests and respond using spoken language (Sarant et al., 2010). Many studies have demonstrated a strong association between language and speech perception ability (for example, Blamey et al., 2001; Niparko et al., 2010).

Cognitive delay has been associated with reduced development of speech perception and production skills in populations of children with diagnosed additional disabilities (Holt & Kirk, 2005; Pyman et al., 2000; Waltzman et al., 2000), but is also a predictive factor for children who are in the average range for non-verbal cognitive abilities (Moog & Geers, 2003). Pisoni and colleagues emphasized the importance of cognitive factors such as memory, attention, and verbal rehearsal speed in determining outcomes after implantation (Pisoni & Cleary, 2003; Pisoni et al., 1999), and postulated that 'central' cognitive factors might explain some of the previously unexplained variance in outcomes for children with cochlear implants (Pisoni & Cleary, 2003; Pisoni et al., 1999). Geers and Sedey (2011) added credence to this theory with their recent observation that faster verbal rehearsal speed contributed to better language outcomes in children implanted between 2 and 5 years of age with more than 10 years of cochlear implant experience. In further support of Pisoni and colleagues' theory, it has recently been reported that when compared to children of the same age and cognitive ability, children with cochlear implants still demonstrate language delays that are disproportionate to their cognitive potential (Meinzen-Derr et al., 2011). The cognitive processes underlying this performance-functional gap need to be investigated and understood in order to implement appropriate intervention strategies to close the gap and improve outcomes for a greater proportion of children with cochlear implants.

#### **4.5 Communication mode**

Communication mode, often dichotomized into oral communication and total communication (signing plus speaking), has long been investigated as a source of variance in outcomes for children with cochlear implants, with mixed results. Proponents of oral communication maintain that maximal auditory benefit from cochlear implants can only be gained if hearing and speech are the only media for communication. There are several reports of children attending oral communication programs achieving higher speech perception and language scores than children in total communication programs (Archbold et al., 2000; El-Hakim et al., 2001; Geers et al., 2003; Meyer et al., 1998; Moog & Geers, 2003). Similarly, speech production outcomes are reported to be better for children in oral education settings. Tobey et al (2003) found oral-aural communication and teaching methods that emphasized speaking and listening to be the most influential factors in determining speech production development in children implanted by age 5 years. These

Cochlear Implants in Children: A Review 355

been shown to demonstrate better communication skills and make higher contributions to

 Unsurprisingly, maternal communication skills are also a significant indicator for language development, early reading skills, and psychosocial development, with children of mothers who are better communicators developing better reading and language skills and having fewer behaviour problems (Calderon, 2000; Niparko et al., 2010). Children with a more highly educated parent caregiver have been reported to have better language, even in studies where the average educational level was relatively high (Geers et al., 2009; Sarant et al., 2009). It has been suggested that the relationship between socioeconomic status and language outcomes is actually mediated solely by properties of maternal speech that differ as a function of socioeconomic status (Hoff, 2003; Hoff & Tian, 2005). Gender also contributes to the variation in outcomes between children, with females consistently achieving better results with regard to speech production (Tobey et al., 2003), reading (Moog

Cochlear implant and speech characteristics such as the number of active electrodes in the implant array, larger dynamic ranges in speech processor maps, greater growth of loudness and length of time using the latest speech processing strategies have been found to significantly influence speech production and language outcomes in children implanted by age 5 years (Connor et al., 2000; Moog & Geers, 2003; Peng et al., 2004; Tobey et al., 2003). The number of surviving nerves has also been postulated to contribute to outcomes (Pyman

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

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

children's progress than non-participating parents (Fallon & Harris, 1991).

& Geers, 2003) and language development (Geers et al., 2009).

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

**4.7 Other factors** 

et al., 2000).

classroom (Cho Lieu, 2004).

environments were found to enhance speech production development, regardless of whether the environment was a mainstream school or a special school, although children in mainstream environments outperformed those in special education environments.

Proponents of the total communication approach maintain that children will obtain maximal information through the use of both speech and some form of manually coded English, as the latter will provide information that may be missed due to insufficient auditory abilities. Improved vocabulary development has been documented for children implanted early and enrolled in total communication educational programs over those in oral programs (Connor et al., 2000). There are also reports that mode of communication does not significantly influence some outcomes. Yoshinaga-Itano and Snyder (1996) found that mode of communication and learning did not significantly affect students' performance in the lexical/semantic characteristics of their written language. They hypothesized that written language is acquired in such a way that students need only one well-established language in order to acquire the written form of their language, and that both oral and signed communication methods may provide students with sufficient bases from which to learn written English. Similarly, several studies of speech perception, production, language, reading and later academic outcomes of children with cochlear implants have not found oral or total communication modes to be predictive of better results (Geers, 2003; Miyamoto et al., 1993; Niparko et al., 2010; Robbins et al., 1999; Uziel et al., 2007).

The absence of overwhelming evidence of the superiority of one communication method over the other may be due to differences in the characteristics of the children studied. Children who are implanted at younger ages are more likely to use an oral communication method, and particular educational programs may also have selection biases towards children with characteristics such as greater preoperative residual hearing or higher cognitive ability (Geers, 2006a). Some non-government funded educational programs are not accessible to families of lower socioeconomic status, and in this way only children from families with greater financial means and likely higher educational achievements will be enrolled in particular programs. When considering the effect of mode of communication, it is unclear in many cases whether children use oral communication after cochlear implantation because they are progressing well, or whether their rate of progress is due to their use of oral communication.

#### **4.6 Family characteristics**

Several family characteristics have been found to contribute to various outcomes for children with hearing loss, including those with cochlear implants. Family size has been observed to impact on speech production outcomes, with children from smaller families making faster progress (Moog & Geers, 2003; Tobey et al., 2003). This is presumably due to the fact that parents of smaller families may have more time and/or resources to devote to assisting their children's communication development. Similarly, children from families of higher socioeconomic status have achieved better speech production, language and literacy outcomes (Connor & Zwolan, 2004; Dollaghan et al., 1999; Holt & Svirsky, 2008; Niparko et al., 2010; Tobey et al., 2003). Greater parental involvement in children's intervention programs has also been associated with improved language development (Moeller, 2000; Sarant et al., 2009; Watkin et al., 2007). This is presumably due to increased follow-up and improved communication at home, as parents who become involved in intervention have

environments were found to enhance speech production development, regardless of whether the environment was a mainstream school or a special school, although children in

Proponents of the total communication approach maintain that children will obtain maximal information through the use of both speech and some form of manually coded English, as the latter will provide information that may be missed due to insufficient auditory abilities. Improved vocabulary development has been documented for children implanted early and enrolled in total communication educational programs over those in oral programs (Connor et al., 2000). There are also reports that mode of communication does not significantly influence some outcomes. Yoshinaga-Itano and Snyder (1996) found that mode of communication and learning did not significantly affect students' performance in the lexical/semantic characteristics of their written language. They hypothesized that written language is acquired in such a way that students need only one well-established language in order to acquire the written form of their language, and that both oral and signed communication methods may provide students with sufficient bases from which to learn written English. Similarly, several studies of speech perception, production, language, reading and later academic outcomes of children with cochlear implants have not found oral or total communication modes to be predictive of better results (Geers, 2003; Miyamoto et

The absence of overwhelming evidence of the superiority of one communication method over the other may be due to differences in the characteristics of the children studied. Children who are implanted at younger ages are more likely to use an oral communication method, and particular educational programs may also have selection biases towards children with characteristics such as greater preoperative residual hearing or higher cognitive ability (Geers, 2006a). Some non-government funded educational programs are not accessible to families of lower socioeconomic status, and in this way only children from families with greater financial means and likely higher educational achievements will be enrolled in particular programs. When considering the effect of mode of communication, it is unclear in many cases whether children use oral communication after cochlear implantation because they are progressing well, or whether their rate of progress is due to

Several family characteristics have been found to contribute to various outcomes for children with hearing loss, including those with cochlear implants. Family size has been observed to impact on speech production outcomes, with children from smaller families making faster progress (Moog & Geers, 2003; Tobey et al., 2003). This is presumably due to the fact that parents of smaller families may have more time and/or resources to devote to assisting their children's communication development. Similarly, children from families of higher socioeconomic status have achieved better speech production, language and literacy outcomes (Connor & Zwolan, 2004; Dollaghan et al., 1999; Holt & Svirsky, 2008; Niparko et al., 2010; Tobey et al., 2003). Greater parental involvement in children's intervention programs has also been associated with improved language development (Moeller, 2000; Sarant et al., 2009; Watkin et al., 2007). This is presumably due to increased follow-up and improved communication at home, as parents who become involved in intervention have

mainstream environments outperformed those in special education environments.

al., 1993; Niparko et al., 2010; Robbins et al., 1999; Uziel et al., 2007).

their use of oral communication.

**4.6 Family characteristics** 

been shown to demonstrate better communication skills and make higher contributions to children's progress than non-participating parents (Fallon & Harris, 1991).

 Unsurprisingly, maternal communication skills are also a significant indicator for language development, early reading skills, and psychosocial development, with children of mothers who are better communicators developing better reading and language skills and having fewer behaviour problems (Calderon, 2000; Niparko et al., 2010). Children with a more highly educated parent caregiver have been reported to have better language, even in studies where the average educational level was relatively high (Geers et al., 2009; Sarant et al., 2009). It has been suggested that the relationship between socioeconomic status and language outcomes is actually mediated solely by properties of maternal speech that differ as a function of socioeconomic status (Hoff, 2003; Hoff & Tian, 2005). Gender also contributes to the variation in outcomes between children, with females consistently achieving better results with regard to speech production (Tobey et al., 2003), reading (Moog & Geers, 2003) and language development (Geers et al., 2009).
