The major components of the MSTB are the Hearing in Noise Test (HINT) and the Consonant/Nucleus/Consonant Test (CNC). The HINT ² provides a measure of speech recognition ability for sentences in quiet and in noise. The background noise is filtered to match the long-term average spectrum of the sentences. In the MSTB, the HINT sentence lists are presented at 70 +dB in quiet and at 10 +dB signal-to-noise ratio (i.e., noise at 60 +dB). Smaller signal-to-noise ratios (e.g., 5 +dB or 0 +dB) may also be used to avoid ceiling effects. Although normal-hearing listeners can comprehend sentences effectively with signal-to-noise ratios of 3 +dB, implant recipients typically show degraded speech recognition when signal-to-noise ratios are reduced beyond 10 +dB.

The CNC consists of lists of monosyllabic words with equal phonemic distribution, with each list having approximately the same phonemic distribution as the English language.³ Such lists provide material for performance testing that is more likely to represent daily experience with speech stimuli. These tests measure percentage of words correctly recognized. Open-set conditions for monosyllabic word recognition are considered the most difficult challenge to a listener with a cochlear implant, and such tests are useful to compare outcomes in adults.⁴ Revised CNC lists⁵ were developed to eliminate uncommon words and proper nouns. Ten lists of 50 words contain monosyllabic words that are employed with a frequency of greater than 4 per 1 million, as calculated in word-frequency tables. As part of the MSTB protocol, during each preoperative and postoperative evaluation, one CNC and one HINT list should be presented in quiet at 70 dB(A). In addition, if the patient performs greater than 30% under quiet conditions, HINT sentences can be presented in noise at 10 +dB signal-to-noise ratio.

Implant Performance in Adults

Improved speech perception is the primary goal of cochlear implantation. Although initial clinical series judged implant efficacy mostly on environmental sound perception and performance on closed-set tests, greater emphasis is now placed on measures of open-set speech comprehension. Speech-perception results from early clinical trials have served to guide the evolution of cochlear implantation. Gantz and colleagues ⁶ provided early comparative data in their assessment of environmental sound and speech perception in a large cohort of nonrandomized single-channel and multichannel implant users. Multichannel implants provided significantly higher levels of performance on all measures. Cohen and associates⁷ performed the first prospective, randomized trial of cochlear implants through the U.S. Veterans’ Administration hospital system. The trial provided high-quality clinical data and convincing evidence of open-set speech recognition, and established the clear superiority of multichannel over single-channel designs. The study was the first to report a low complication rate and high device reliability in individuals deafened after language acquisition from multiple centers with varying levels of prior programmatic implant experience.

Cohen and Waltzman,⁸ Skinner and colleagues,^9,¹⁰ and Wilson and associates¹¹ assessed effects of changing external processing capabilities. They compared the performance of subjects fitted with processors designed to increase the rate of information transfer through higher rates of pulsed stimulation. Each study assessed a different processor, and study design and processing strategy also differed among studies. In each study, the use of a more sophisticated speech processor led to significantly better performance in open-set speech recognition.

Clinical observations in patients with current processors indicate that for patients with implant experience longer than 6 months, the mean score on open-set word testing approximates 25% to 40% (range 0% to 100%).^7,¹²^–¹⁴ Results achieved with the most recently developed speech processing strategies reveal mean scores greater than 75% on words-in-sentence testing (range 0% to 100%). Although subjects perform substantially poorer on single-word testing, these mean scores continue to improve as speech-processing strategy evolves.¹⁰ After implantation, speech recognition by telephone¹⁵ and music appreciation are often observed.

Benefits are enhanced through the use of more recently developed processing strategies. Spahr and colleagues ¹⁶ observed that differences in implant design affect performance, especially in difficult listening situations. Input dynamic range and the method by which compression is implemented seem to be the major factors that account for results in difficult listening situations, with greater performance associated with the expanded dynamic range offered by current processing strategies employed by the Advanced Bionics and MedEl devices.

Predictors of Benefit in Adults

Assessments of speech recognition in adults with cochlear implants offer the opportunity to develop models of benefit prediction. As investigators identify the salient predictive factors, candidacy, device and processing strategy, and the degree of postoperative auditory rehabilitation necessary, they can be better informed. The contributions of modifiers to differences in performance (multivariate analysis) have been addressed in several large studies.^6,^7,¹²–¹⁴,¹⁷–¹⁹ The following factors have been evaluated:

• Subject variables: age of onset, age of implantation, deafness duration, etiology, preoperative hearing, survival and location of spiral ganglion cells, patency of the scala tympani, cognitive skills, personality, visual attention, motivation, engagement, communication mode, and auditory memory

• Device variables: processor, implant, electrode geometry, electrode number, duration and pattern of implant use, and strategy employed by the speech processing unit

Although the significance of the above-listed factors varies across different populations, multiple regression analysis has identified variables with high predictive value for speech comprehension. Length of implant use accounts for a high degree of variance in speech perception measured postoperatively. When length of use is controlled, preoperative hearing (particularly with respect to speech recognition) also accounts for a high degree of variance. Duration of deafness, age of implantation, cochlear patency, subject engagement with the therapeutic regimen, and processor type also carry high predictive values for speech understanding.

In addition to the factors in the list, the choice of ear to implant is a highly compelling issue. Other studies have emphasized the utility of implanting the better hearing ear.¹³ At Johns Hopkins Hospital, we have long advocated the implantation of the poorer hearing ear. Although more data are needed, our studies so far reveal no significant difference in implant performance based on whether the better or worse hearing ear is implanted. Figure 160-1 shows a regression plot of the predicted postoperative word scores for each patient as modeled by the Johns Hopkins (implant poorer ear) and Iowa formulas (better ear).¹⁷ Virtually identical scores are predicted on the basis of each patient’s duration of deafness and preoperative sentence recognition scores. These data suggest that results obtained through cochlear implantation of the poorer hearing ear are statistically equivalent to results obtained through implantation of the better hearing ear. The similarity of results obtained through both methods suggests that implantation may have a beneficial effect on central auditory pathway development regardless of sidedness.

Figure 160-1. Regression plot of the predicted postoperative word scores for each patient as modeled by the Johns Hopkins (implant poorer ear) and Iowa formulas (better ear). There are virtually identical scores predicted on the basis of each patient’s duration of deafness and preoperative sentence recognition scores. These data suggest that results obtained through cochlear implantation of the poorer hearing ear are statistically equivalent to results obtained through implantation of the better hearing ear. The similarity of results obtained through both methods suggests that implantation may have a beneficial effect on central auditory pathway development regardless of sidedness. CNC, Consonant/Nucleus/Consonant Test.

Another variable that influences speech perception is technologic sophistication of the implanted device. Improvements in speech perception have been associated with generational improvements in signal processing strategies, speech processors, and electrode arrays,²⁰ but may reflect clinical trends and technologic advances.¹³ Criteria for cochlear implant candidacy are constantly expanding. Research has shown that patients with greater residual hearing show even more promising results. Identification of monosyllabic words for individuals using early generations of the Nucleus (Cochlear Corp., Sydney, Australia) multichannel cochlear implant averaged 16%,⁶ whereas performance exceeds 50% on similar measures with current technology.^10,¹⁶ Earlier studies have contrasted performance across different manufacturers of devices. Differences in performance seem more closely related, however, to general demographic differences across patient populations, tests used, and length of experience with the devices than to differences in characteristics of like-generation devices per se.^21,²²

Cochlear Implantation with Hearing Preservation in Adults

There has been considerable interest in clinical strategies that combine residual acoustic hearing with electric hearing provided by a cochlear implant. Two strategies have been developed, depending on baseline hearing status. A combined mode uses a cochlear implant in one ear and a hearing aid in the other ear.²³ A hybrid strategy uses a hearing aid and a cochlear implant in the same ear.^24,²⁵

The goal of combining amplification with a cochlear implant in the opposite ear is to preserve perceptual advantages inherent in (predominantly low frequency) acoustic hearing in an attempt to capture at least some binaural cues. In fact, binaural advantages are observed in some patients.²³ Tests of speech perception in noise reveal trends toward a binaural advantage for word recognition depending on the direction of origin of noise (with advantages obviated when noise is on the hearing aid side). Localization ability improved with both devices. These data support the use of a hearing aid opposite a cochlear implant for appropriate patients.

Success with hearing preservation ^26,²⁷ in ears implanted with scala tympani electrodes has encouraged the development of hybrid modes of stimulation—electroacoustic hearing. Various surgical strategies have been adopted in attempts to limit cochlear trauma with scala tympani electrode insertion, enhancing opportunities for preserving residual (typically, <1 kHz) hearing. Hearing preservation procedures are designed to avert basilar membrane rupture and attendant spiral ganglion cell loss. Optimal preservation seems to be achieved with placement of the cochleostomy in a strategic location (away from the basilar membrane) along with cautious insertion of adapted, smaller arrays in a manner that limits impact on the endosteal and basilar membrane surfaces.²⁸

Electroacoustic hearing seems to confer distinct advantages in speech perception and in music listening.^25,²⁹ Improvements in speech-in-noise understanding and melody recognition are linked to the ability to distinguish fine pitch differences through preserved, low-frequency acoustic hearing. There may be expanded spectral representation that more faithfully supports higher frequency hearing over time.³⁰ These observations suggest that the preservation of residual low-frequency hearing should be considered in selected patients. Observations of advantages in electroacoustic hearing may expand candidate selection criteria for cochlear implantation.

Although electroacoustic stimulation is a promising treatment for patients with residual low-frequency hearing, a small subset lose residual hearing despite best attempts with preservation. Such patients may obtain expected levels of benefit using the electric mode of the hybrid implant alone. For patients unable to achieve this benefit from an electroacoustic strategy after losing residual hearing, reimplantation with a standard array seems to provide higher levels of speech recognition.³¹

Implant Performance in Children

Pediatric cochlear implantation began with House-3M, single-channel implants in 1980. Investigational trials with multichannel cochlear implants began with adolescents (10 to 17 years old) in 1985 and with children (2 to 9 years old) in November 1986. Implantation of infants and toddlers younger than 2 years began in 1995.³² Although clinical experience with cochlear implantation is shorter in children than in adults, a large body of clinical reports is now available.^33,³⁴ Investigators have evaluated the hearing and speech receptive benefit of cochlear implants in children since 1985.

Auditory Performance Assessments for Children

Auditory performance in children is assessed with a battery of audiologic tests that can address the wide range of perceptual skills exhibited by children with severe-to-profound sensorineural hearing loss. Although substantial auditory gains are apparent in implanted children, the range of quantifiable improvement varies widely among children, and depends heavily on the duration of use of the device, preoperative conditions, and longitudinal experience and training effects. For this reason, testing should survey a range of levels of speech recognition, including simple awareness of sound, pattern perception (discrimination of time and stress differences of utterance), closed-set (multiple choice) speech recognition, and open-set (auditory only) recognition.

Methodologic variables must be considered when attempting to rate objectively the effect of cochlear implants on the development of speech perception in deaf children. Difficulties are inherent in objectively rating communication competence in very young children. Older children may exhibit advantages by virtue of greater familiarity with a test’s context, independent of perceptual skills. Objective assessment mandates a structured setting that is not always conducive to eliciting a child’s best cooperative effort. Investigators must also account for discontinuity in the age-appropriate measures necessary for longitudinal assessment.³⁴ Methodologic challenges and developmental considerations inherent in pediatric implant assessment have been examined in detail by Kirk and Diefendorf,³⁵ who categorized variables as relating to the following:

• Internal variables: the child’s age and level of language and cognitive development

• External variables: the child’s ability and willingness to respond as influenced by reinforcement and required memory task

• Methodologic variables: the procedure of voice presentation, the test administered, and the available options from which to choose a response

Tests of speech perceptions typically used for childhood assessment have been described in detail,^1a,³⁵–³⁷ and usually consist of closed-set tests that assess word identification among a limited set of options with auditory cues only, open-set tests (scored by percentage of individual words correctly repeated), and structured interviews of parents using criteria-based surveys³⁸ to assess response to sound in everyday situations and behaviors related to spoken communication.

Early Studies of Speech Reception in Children with Cochlear Implants

House and colleagues ³⁹ found that children with cochlear implants obtain substantial improvement in auditory thresholds, closed-set speech recognition, and limited open-set speech recognition with the House-3M single-channel implant. Miyamoto and coworkers⁴⁰ provided systematic, well-controlled assessments of childhood cohorts and consistently showed performance advantages of multichannel over single-channel implants. Other early studies by Fryauf-Bertschy,⁴¹ Gantz,⁴² Miyamoto,¹⁸ and Waltzman⁴³ and their colleagues observed that implanted children gain substantial speech perceptive capabilities for 5 years after implantation. Because many of the implanted children tracked in these studies were congenitally or prelingually deaf, there are compelling data to indicate that implantation can provide auditory access during critical developmental stages to form the early correlates of spoken language.

The studies we have cited have shown implant benefit in children with total or near-total hearing loss. An important issue for candidacy of children with lesser degrees of hearing impairment is the study of implant benefit relative to controls who have not received implants. Classification of children according to preoperative hearing levels can provide a common ground for comparison. Miyamoto and associates ⁴⁴ described the following candidacy scale for stratifying children according to aided pure-tone detection thresholds: “Gold” class hearing aid users have unaided thresholds of 90 to 100 dB at two of three frequencies (0.5 kHz, 1 kHz, 2 kHz), with a mean of 94 dB. “Silver” class hearing aid users have unaided thresholds of 101 to 110 dB at two of three frequencies, with a mean of 104 dB. “Bronze” class users have unaided thresholds of greater than 110 dB at two of three frequencies, with a mean greater than 110 dB.

Hearing aid users in the “gold” category generally fall into Boothroyd’s ⁴⁵ category of “considerable residual hearing.” In many such cases, hearing aid users that function at this level show substantial capabilities for near-normal trajectories of speech and oral language acquisition. This particular group of profoundly hearing-impaired children sets a comparative standard for speech perception performance. “Silver” category hearing aid users receive few spectral cues and rely heavily on temporal cues for speech perception. “Bronze” category users are considered “totally deaf,” and receive only low-frequency percepts and restricted or no temporal cues.

Most hearing-impaired children who have received cochlear implants fell into or were eventually moved into the “bronze” category. Compared with children using amplification, children with implants have shown the following:

• After 2 years of implant experience, mean speech intelligibility scores of implanted children surpass those of “silver” category hearing aid users and approach within 10% scores of “gold” category users, particularly on more stringent tests of speech comprehension.^44,⁴⁶ Longitudinal tracking of implanted children shows no evidence of a plateau effect in mean scores of speech comprehension. In conjunction with evidence based on multivariate analysis, this observation suggests that length of implant use is the primary determinant of receptive benefit.

• Trends toward continued improvement in speech reception are also associated with improved intelligibility of speech.⁴⁷ Although the measured proficiency of speech produced remains low through the first 2 years after implantation, intelligibility scores thereafter show dramatic gains and surpass those of hearing aid users in the “silver” category.⁴⁸ These observations are consistent with observations of gains in speech intelligibility in other childhood cohorts.^49,⁵⁰

More Recent Studies of Speech Reception in Children with Cochlear Implants

Between 1994 and 2004, numerous reports documented various levels of gains in speech recognition in young deaf children using multichannel cochlear implants. Miyamoto and coworkers ¹⁸ noted that in 29 children with 1 to 4 years of experience with a cochlear implant, approximately one half achieved open-set speech recognition. Waltzman and Cohen⁵¹ found that 14 children implanted before age 3 years attained high levels of speech perception performance with only 2 years of experience. Fryauf-Bertschy and coworkers⁵² examined speech perception in cochlear-implanted children over 4 years, and noted significant increases in pattern perception and results of closed-set speech perception tests.

Variability in speech-perception performance across subjects is widely recognized, and is related to several variables, including age of implantation,^33,^42,⁵²^–⁵⁴ mode of communication,^43,⁵⁵ family support,⁵² and length of deafness.^56,⁵⁷ Miyamoto and colleagues⁴⁰ found that duration of deafness, communication mode, age at onset of deafness, and type of processor accounted for approximately 35% of variance in closed-set testing. The length of implant use alone accounted for a larger percentage of variance on all speech perception measures. In a 5-year follow-up study, O’Donoghue and associates⁵³ found that age at implantation was the most significant covariant, and that mode of communication was the most significant between-individuals factor. The latter study showed that young age at implantation and oral communication mode are the most important known determinants of later speech perception in young children after cochlear implantation.

Waltzman and colleagues ⁴³ and Brackett and Zara⁵⁸ reported improved speech reception in children implanted at age 2 to 3 years compared with children implanted at an older age. Multicenter data reported by Osberger and associates⁵⁹ indicated that implant performance of children implanted before age 2 years is significantly better than implant performance of children implanted between age 2 and 3 years. The authors also identified an important confounding variable, however, that exists in the children who receive a cochlear implant at a younger age: they are more likely to use an oral mode of communication. This, by itself, may be a predictor of higher implant performance—an observation borne out in early studies of a national childhood cohort assembled by Geers and colleagues.⁵⁵

Osberger and coworkers ⁵⁹ also found that children with more residual hearing relative to earlier cohorts were undergoing implantation. Gantz and colleagues⁶⁰ compiled data from across centers that indicate children with some degree of preoperative open-set speech recognition obtain substantially higher levels of speech comprehension. Taken together, these studies suggest the strongest potential for benefit exists with implantation at a young age, when intervention is provided early and, in the case of a progressive loss, before auditory input is lost completely.

Cheng and associates ³³ performed a meta-analysis of relevant literature on speech recognition in children with cochlear implants. Of 1916 reports on cochlear implants published since 1966, 44 contained sufficient patient data to compare speech recognition results between published (n = 1904 children) and unpublished (n = 261) trials.³³ Meta-analysis was complicated by the diversity of tests required to address the full spectrum of speech reception in children with cochlear implants. An expanded format of the Speech Perception Categories⁶¹ was designed to integrate results across studies. The main conclusions of this meta-analysis were that earlier implantation is associated with a greater trajectory of gain in speech recognition (Fig. 160-2), performance comparing deafness of congenital and acquired etiologies levels out over time, and there is an absence of reaching a plateau of speech recognition benefits over time. More than 75% of the children with cochlear implants reported in peer-reviewed publications have achieved substantial open-set speech recognition after 3 years of implant use.

Figure 160-2. Meta-analysis of speech perception results with cochlear implantation in children, showing effects of age at implantation on speech perception. Published and unpublished data are shown. Three different ages at implantation groups are compared (<4 years, 4 to 5 years, and >6 years). The ordinal scale represents levels of speech perception: 1, detection; 2, pattern; 3, limited closed-set; 4, substantial closed-set; 5, limited open-set; and 6, substantial open-set.

Implantation of Infants

New diagnostic approaches and improved treatment options have enhanced real-life outcomes and transformed clinical approaches to the treatment of early-onset hearing loss. Universal newborn hearing screening now routinely identifies hearing loss that might have gone unnoticed in years past until a child had failed to develop language skills. Such early identification affords the opportunity to provide clinical intervention during a brief and critical growth period when neural connections develop physiologic support needed for children to achieve verbal communication.

A growing body of evidence supports the early application of cochlear implantation in congenitally deaf children. Meta-analyses of the effects of age at implantation have shown that children undergoing implantation at younger ages achieve greater progress in speech perception skills than children implanted at older ages.^33,^62,⁶³ Because the development of language follows the same trajectory as that reflecting speech perception, language growth is more favorable in children who receive cochlear implants early in life.⁶⁴ To the extent that higher language ability results in greater independence in school settings,⁶⁵ earlier intervention would enhance the cost-effectiveness of the cochlear implant.

Cochlear implantation has been shown to be a safe procedure in children younger than 12 months old.^66,⁶⁷ The motivation to pursue implantation when a child has been deemed an appropriate candidate is supported by compelling data showing the benefits of earlier intervention. Tait and colleagues⁶⁸ showed that preverbal skills develop much more rapidly in children who receive cochlear implants before 2 years of age compared with children implanted between 2 and 3 years old, or between 3 and 4 years old. Connor and colleagues⁶⁹ examined latent growth curves and showed the value of very early implantation as it translated into more favorable outcomes. Dettman and colleagues⁷⁰ in Australia and Lesinski-Schiedat and associates⁷¹ in Germany have convincingly shown with longitudinal assessment that the language trajectories of children implanted before age 12 months are greater than those achieved with implantation after 12 months of age.

Nicholas and Geers ⁷² showed that language outcomes for deaf children for whom appropriate intervention occurs within the first months of life are far superior to outcomes associated with later intervention. They noted that the first 3 years in a child’s life are crucial for acquiring information about the world, communicating with family, and developing a cognitive and linguistic foundation from which all further development unfolds.

Because of the demonstrated safety of early implantation and the effectiveness of early linguistic intervention, cochlear implantation in younger children (12 months old) has been approved by the Food and Drug Administration in the United States. The current approval for implantation at age 12 months should be interpreted with caution. The intent of that approval is based on open market applications from manufacturers; delaying intervention results and the risk of prolonged auditory deprivation and adverse consequences for development should be weighed in each individual case.

Bilateral Cochlear Implantation

In an effort to expand the benefits obtained with unilateral cochlear implantation, bilateral implantation has been pursued in increasing numbers of patients, either simultaneous or sequential. As of this writing, approximately 20% of all implant users have bilateral devices based on generally positive subjective experiences with low rates of complication. An important development within the field of cochlear implantation is to assess fully the impact of bilateral intervention.

Normal listeners possess a range of auditory capabilities owing to binaural processing, as follows:

Localization: Normal listeners are able to tell where sound is coming from in the horizontal plane (at ear level) with an accuracy of ±14 degrees.⁷³ The brain uses differences in intensity and time between the two ears to determine the location of a sound source. To localize sound in the vertical plane (up and down), or when time and intensity cues between the two ears are ambiguous, spectral (pitch) information is important.⁷⁴ The shapes of the outer ear and ear canal change the intensities of all of the pitches arriving at the ear (by reflecting them differently) to determine the location of sounds in the vertical plane.⁷⁵

Head shadow: When listening to speech in noise, the head acts as a sound barrier that makes noise quieter on the side away from the speech. When one ear is close to the noise source, adding the other ear (away from the noise) provides a second ear where the speech is louder than the competing noise.

Squelch: When signals and noise come from different directions, the brain is able to separate them by comparing time, intensity, and pitch differences between the two ears. The practical effect is that the brain is able to suppress signals that the listener does not wish to hear.

Summation: When identical signals are presented to the two ears, there is an advantage when hearing with both ears instead of just one alone. The brain has a special ability to use the signals from both ears to produce this binaural advantage.

Studies of subjects with unilateral hearing loss illustrate some of the problems that a listener with only one “good” ear may encounter. Background noise often interferes with word recognition in quiet and noisy conditions even when the speech is directed to the good ear. People have reported difficulty hearing and understanding speech even in relatively quiet situations that include low-level noise (e.g., car radios, air conditioners).⁷⁶ Children with unilateral hearing loss not only have difficulty in noise,⁷⁷ but also show delays in language development and academic performance relative to their peers with normal hearing.⁷⁸

In addition to the general advantages of binaural hearing, there may be other compelling reasons for considering bilateral implantation in very young children. Congenitally deaf children depend on their cochlear implants for learning spoken language. Children with normal hearing acquire language through incidental learning—that is, through participation in everyday communication and social experiences, which are often unintended and incidental. Although studies have shown improved language acquisition in children with unilateral implants relative to their preimplant performance with hearing aids,^64,⁷⁹ children still lag behind their peers with normal hearing in mastery of more complex language structures that are requisites for academic success.⁸⁰ If a young deaf child has two implants, the rate of incidental language learning is likely to be accelerated because they would be better able to understand speech in everyday situations (most of which are noisy), and to localize to the most relevant (speech) events in their environment. The improved benefits with bilateral implants in young deaf children have important implications for language acquisition, academic success, and educational and occupational opportunities.

Providing sound input to both ears in a young deaf child ensures that sound is processed on both sides of the brain. The right and left auditory cortices can develop in a more normal sequence. If a child is implanted on only one side, the parts of the brain that would have been stimulated by the nonimplanted ear do not develop, and eventually plasticity is greatly diminished. Ryugo and colleagues ⁸¹ reported that electric stimulation of the auditory system largely prevents or reverses the synaptic abnormalities seen in congenitally deaf white cats.

Reports of the bilateral benefits experienced by adult and pediatric patients with two implants continue to increase.⁸²^–⁹¹ There are few prospective studies of children who receive two implants during early childhood, however.

Although the “era of bilateral implantation” has been introduced, there are few controlled trials to date.⁹² Preliminary results reveal evidence of an expanded sound field and loudness summation, and some level of sound localization ability to most bilateral recipients. In a few patients, benefits attributable to effective squelch are noted. Such findings show central integration of electric stimulation from the two ears despite an absence of precise tonotopic matching of binaural inputs. Systems that enable integrated speech processing of inputs from the bilateral sound fields have yet to be introduced clinically. It is uncertain whether potential benefits of bilateral implantation could be expanded through such processing.

Language Development in Children

A primary goal of implantation in children is to assist comprehension and expression through the use of spoken language. Language is defined as a vehicle for shaping and relating abstractions for communication.⁹³ The meaning of language-mediated abstraction is independent of the immediate situation. Practical use of language is based on the assignment of a single name to various appearances and situations under varying conditions. Information exchange via spoken language involves a conversion of thought into speech. This conversion relies on mental representations of phonologic (sound) structure and syntactic (phrase) structure.

All fundamental models of language development propose that the acquisition of language is the result of progressive organization from an initially undifferentiated state. As incremental differentiation occurs, language skills become more sophisticated and hierarchically integrated. The child first must learn to form internal representations of acoustic speech patterns (Fig. 160-3). These experiences enable a child to identify consistent patterns in phonologic inputs and to develop associations between context and semantic and syntactic patterns. Through increased familiarity, these associations between spoken language and their actual counterparts build a child’s semantic awareness.⁹⁴ Social cognition and emotional needs are likely to encourage such development, as supported by observations that infants become “tuned” to their language environment in the form of “perceptual maps” (Fig. 160-4),⁹⁵ and show protolinguistic behaviors with caretakers that are bidirectional.⁹⁶^–⁹⁸

Figure 160-3. The cycle of verbal communication. Hearing is crucial to the process of verbal communication and allows for verbal comprehension. Concept formation gives rise to expressive language and speech articulation capabilities, which are applied as verbal language in appropriate situations. Successful verbal communication ultimately depends on hearing.

(Modified from the Reynell Developmental Scales Manual. Los Angeles: Western Psychological Services.)

Figure 160-4. Left, Schematic figure shows natural auditory boundaries according to F₁ and F₂ formant frequencies. These boundaries are thought to provide a framework by which infants process incoming sound streams into gross categories. Intrinsic phonetic differences separate boundary regions from one another. Right, The ability to partition auditory input according to these boundaries is independent of linguistic experience, and is present throughout various languages. Examples of vowel processing in three different languages (Swedish, English, and Japanese) are shown.

(Adapted from Kuhl PK, Meitzoff A. Speech as an intermodal object of perception. In: Yonas A, ed. Perceptual Development in Infancy. Hillsdale, NJ: Lawrence Erlbaum Associates; 1988:235-266; and Kirk KI. Challenges in the clinical investigation of cochlear implant outcomes. In: Niparko JK, ed. Cochlear Implants: Principles and Practices. Philadelphia: Lippincott Williams & Wilkins; 2000:225-259.)

Early communication between infants and caregivers forms a critical foundation for development. This foundation provides a base on which cognition, affect, and social interaction may evolve.⁹⁹ If communication is hindered, development fails to proceed normally, with detrimental sequelae in terms of cognitive, behavioral, and social development. Hearing loss and subsequent obstacles to communication threaten optimal development.¹⁰⁰^–¹⁰² Because most children who have sensorineural hearing loss are born to hearing parents, a “mismatch” may exist between child and parent¹⁰³ that prevents effective communication.^104,¹⁰⁵ Because sign language skills in hearing parents tend to be absent or basic, such children are at further risk for developmental delay.^106,¹⁰⁷ Additional evidence confirms that children with sensorineural hearing loss who engage in linguistic interactions with their parents show age-appropriate cognitive, social, and behavioral development.¹⁰⁰ More recent theories suggest the processes linking language to cognition, affect, and behavior are dynamic and bidirectional, rather than discrete or independent.^108,¹⁰⁹

For successful bidirectional communication to occur within the family unit, language must be linked to cognition, affect, and behavior. Visual attention, which may be reliably assessed at 4 months of age, is crucial for guiding development.^99,¹¹⁰ Data suggest that visual attention is highly relevant to the development of emotional bonds to caregivers, language learning, and the processing of perceptual information.¹¹¹^–¹¹⁴ In normal development, much of this early visual attention is actually directed by sound. Infants look longer in the direction of sound and longer at visual events whose temporal rhythms match what they hear.^115,¹¹⁶ When sound perception is impaired, visual and auditory integration is similarly disrupted, forcing a child with sensorineural hearing loss to rely on vision for communication and cues about when and where to direct attention.^117,¹¹⁸ This notion has been confirmed in studies of hearing-impaired children using computerized task performance measures.^117,^119,¹²⁰ These impairments have been found to contribute to behavioral problems.¹²⁰ By comparison, two studies found that children with cochlear implants perform better on this computerized task than children without cochlear implants.^117,¹¹⁹

In addition to visual attention, other types of preverbal communication underlie the acquisition of verbal language. Substantial gains in prelinguistic behaviors, including eye contact and turn-taking,¹²¹ and in verbal spontaneity¹²² are observed as early correlates of implant benefit, developing within 6 months of implantation in young children.¹²³ Tait and associates¹²⁴ found that preverbal measures obtained 12 months after implantation are predictive of late performance on speech perception tasks. They observed a significant association between the preverbal measure of “autonomy” obtained before implantation and later speech perception performance. This latter finding has important theoretic implications for understanding of language development, and suggests that intervention that promotes autonomy in adult-child interaction may lead to improved outcomes. Such intervention can be introduced as soon as deafness is discovered.

Language Acquisition in Children with Cochlear Implants

By improving auditory access, cochlear implants augment sound and phrase structure. Although difficult to characterize, benefits in receptive language skills and language production after implantation are the crucial measure by which effectiveness of implants in young children should be assessed. One approach is to compare language performance on standardized tests. The Reynell Developmental Language Scale evaluates receptive and expressive skills independently.¹²⁵ These scales have been normalized on the basis of performance levels of hearing children in an age range of 1 to 8 years, and have been used extensively in populations of deaf children. Although deaf children without cochlear implants achieved language competence at half the rate of normal-hearing peers, implanted subjects exhibited language-learning rates that matched, on average, those of their normal-hearing peers.^125,¹²⁶ In a study of 23 children who became deaf before 3 years of age, Svirsky and colleagues¹²⁶ studied language development after cochlear implantation. The average age of implantation in this cohort was approximately 4 years. These investigators found that speech development progressed at a decreased rate before implantation, but that after implantation, language development in implanted children was parallel to that of normal-hearing children (Fig. 160-5). The implication of this study is that differences in language delay between implanted and normal-hearing children could be explained by the initial period of deafness before implantation, rather than performance or progress after implantation. These findings also emphasize the importance of early implantation. Data are rapidly being gathered to confirm that earlier implantation might limit early language delays to enable more age-appropriate language acquisition.

Figure 160-5. The effect of cochlear implantation (CI) in children on language development. Solid line depicts normal language development as it correlates to chronologic age. Dashed line shows the developmental delay that occurs in deafness before CI. After CI, language development progresses at the same rate as children with normal hearing. This suggests that language delay is a product of cumulative deficits acquired before CI, rather than from impaired progress after CI.

(Modified from Svirsky MA, Teoh SW, Neuburger H. Development of language and speech perception in congenitally, profoundly deaf children as a function of age at cochlear implantation. Audiol Neurootol. 2004;9:224-233.)

Robbins and associates ¹²⁵ noted that implantation improved language-learning rates for children in oral communication and total communication settings based on the Reynall Developmental Language Scale. Geers and coworkers,⁵⁵ also assessing language skills in implanted children enrolled in oral communication and total communication settings, found that the groups did not differ in language level, although the oral group showed significantly better intelligibility in their speech production.

Delays in receptive and expressive language among hearing-impaired children have consistently been documented in the literature, although such delays are not strongly related to degree of hearing loss.^127,¹²⁸ Performance on language measures can be influenced by the child’s mode of communication such that results may not directly reflect the influences of auditory perception or prosthetic intervention. Clinical findings support the hypothesis, however, that some deaf children are able to use the acoustic-phonetic cues provided by the implant in ways that may reduce the language gap between normal-hearing and deaf children.

Central nervous system processing is a primary determinant of the level of verbal language ultimately attained after cochlear implantation.¹²⁹ Pisoni¹²⁹ assessed performance in two groups of pediatric cochlear implant users: “Stars” were children whose phonetically balanced kindergarten scores placed them in the top 20%. The second group, children with scores in the bottom 20%, comprised the control group. Speech perception, spoken word recognition, speech intelligibility, and language level were compared between the two groups at preimplantation and at yearly postimplant intervals. Children in the “Stars” group did not score consistently better on all behavioral measures than children in the control group. Differences between the groups were manifest only on specific tests and task demands. Children with superior implant performance were consistently better on measures of speech perception (i.e., vowel and consonant recognition), spoken word recognition, comprehension, language development, and speech intelligibility than were the control children. The two groups did not differ, however, in their vocabulary knowledge, nonverbal intelligence, visuomotor integration, or visual attention. It was concluded that “Star performance” on measures of spoken language processing and speech intelligibility was not attributed to global differences in overall performance, but to differences specifically in the task of processing auditory information provided by the cochlear implant.

The authors also examined the differential performance on various behavioral tests of communicative ability administered after 1 year of cochlear implant use. Strength of correlation revealed a significant association between spoken word recognition, language development, and speech intelligibility for the “Stars” group, but not for the control group. “Star performance” seemed to result from an enhanced language processing ability and the development of phonologic and lexical representations.

The strong relationship between spoken word recognition and speech intelligibility for superior implant performers suggests that (1) a transfer of knowledge exists between speech perception and production, and (2) that speech perception and production share a common system of internal representation. According to Pisoni and Geers,¹³⁰ the exceptional performance of the “Stars” seems to be a result of their superior abilities to perceive, encode, and retrieve information about spoken words from lexical memory. They described the capacity for processing tasks that require the manipulation and transformation of the phonologic representations of spoken words as “working memory.” Pisoni and Geers¹³⁰ then investigated the impact of working memory on measures of speech perception, speech intelligibility, language processing, and reading in implanted children with prelingual deafness. The investigators evaluated correlations between children’s ability to recall lists of orally presented digits and their performance on these measures. The authors observed correlations between auditory memory and performance in each outcome area, suggesting that working memory plays an important role in mediating performance across these higher communication tasks.¹³⁰

Promising clinical studies have generally supported wider application of cochlear implants in children. Childhood implant research has often relied, however, on case-series design, based in a single center that evaluated children who used different generations of implant technology. Few studies have examined the impact of cochlear implants on the “whole” child, particularly when one considers the importance of understanding longitudinal measures of cognitive, social, and behavioral development. There is also little information available on the perceived benefit of childhood implantation from a perspective of cost-effectiveness.

The need and significance of this information is underscored by the fact that clinical decisions to pursue early cochlear implantation are often prompted by parental choice. Parents of deaf children choose among options which have vastly different implications for the use of medical, (re)habilitative, educational, and other societal resources. A pressing issue concerns the validity of generalizing from early observations of benefit from cochlear implantation to the decision to implant younger children. Should very young infants identified with severe to profound sensorineural hearing loss undergo cochlear implantation within weeks of diagnosis?

An ongoing multicenter study is examining the clinical modifiers of postimplant developmental outcomes, including oral language acquisition, speech recognition skills, selective attention and problem-solving skills, behavioral and social development, parent-child interactions, and quality-of-life measures in children undergoing implantation in six U.S. implant centers.¹³¹ It is hoped that a detailed assessment of communicative and psychosocial results will contribute to an understanding of the factors predicting implant-associated language use, communication competence in early childhood, and the perceived value of early cochlear implantation in light of associated costs. It is hoped that conclusions will enable an informed approach to implant candidacy when considering (re)habilitative strategies designed to enhance developmental learning in children with severe to profound sensorineural hearing loss.

Outcomes after Cochlear Implantation

Educational Placement and Support of Implanted Children

A hearing-impaired child is at substantial risk for educational underachievement.^132,¹³³ Educational achievement by a hearing-impaired child can be enhanced by verbal communication. Traditional methods of speech instruction are more successful with children who have enough residual hearing to benefit from early devices of hearing rehabilitation.¹³⁴ Improved speech perception and production provided by cochlear implants offer the possibility of increased access to oral-based education and enhanced educational independence.

Francis ¹³⁵ and Koch¹³⁶ and their colleagues tracked the educational progress of implanted children by using an educational resource matrix to map educational and rehabilitative resource use. The matrix was developed on the basis of observations that changes in classroom settings (e.g., into a mainstream classroom) are often compensated by an initial increase in interpreter and speech-language therapy. Follow-up of 35 school-aged children with implants indicated that, relative to age-matched hearing aid users with equivalent baseline hearing, implanted students are mainstreamed at a substantially higher rate, although this effect is not immediate, and requires rehabilitative support to be achieved. Within 5 years after implantation, the rate of full-time assignment to a mainstream classroom increases from 12% to 75% (Fig. 160-6).

Figure 160-6. Matrix of educational resource usage by children with cochlear implantation (CI). A, The Educational Resource Matrix (ERM) plot classroom placement (ordinate) versus rehabilitative (speech-language and interpretive) support (abscissa). B, Patterns of change in use of educational resources in a cohort of children within 3 years of CI. C, Patterns of change in use of educational resources in a cohort of children 3 to 6 years after CI. Note the higher levels of mainstreaming, and reduced use of support services with prolonged use of the cochlear implant.

(A, From Koch ME, Wyatt JR, Francis HW, Niparko JK. A model of educational resource use by children with cochlear implants. Otolaryngol Head Neck Surg. 1997;117:174-179; B, from Francis HW, Koch ME, Wyatt JR, Niparko JK. Trends in educational placement and cost-benefit considerations in children with cochlear implants. Arch Otolaryngol Head Neck Surg. 1999;125:499-505.)

Quality of Life and Cost-Effectiveness

Prior studies of the cost-utility of cochlear implants have assessed quality of life and health status to determine the utility gained from cochlear implants.^19,^137,¹³⁸ Utility is a concept that reflects the true value of a good or service. Cost-utility methods determine the ratio of monetary expenditure to change in utility as defined by a change in quality of life over a given period. The assessment of cost-utility is based on the following:

Life-years is the mean anticipated number of years of implant experience based on a life-expectancy analysis of the participating cohort. The change in health utility reflects the difference between preimplant and postimplant scores on survey instruments that have been designed and validated to reflect quality of life. In the United States, England, and Canada, health interventions with a cost-utility ratio less than $20,000 (U.S.) are generally considered to represent acceptable value for money expended (i.e., they are “cost-effective”).¹³⁹^–¹⁴¹

Quality-of-Life Studies in Adults and the Elderly

Costs per quality-adjusted life-year (QALY) for cochlear implants in adult users were determined using cost data that account for the preoperative, postoperative, and operative phases of cochlear implantation.^19,¹³⁸ Benefits were determined on the basis of functional status and quality of life. The precise cost-utility results varied among studies, mostly because of methodologic differences in the determination of benefit, level of benefit obtained, and differences in costs associated with the intervention. Nonetheless, these appraisals consistently indicated that the multichannel cochlear implant in adult populations is associated with cost-utility ratios in the range of $14,000 to $18,000/QALY, indicating a highly favorable position in terms of cost-effectiveness (Table 160-1).

Table 160-1 Cost-Utility Ratio of Cochlear Implantation in Adults

Hearing impairment is one of the most common clinical conditions affecting elderly individuals in the United States.¹⁴² Hearing loss is so profound in 10% of elderly hearing-impaired individuals that little or no benefit is gained with conventional amplification.¹⁴³ Assessing the effectiveness of cochlear implants in elderly patients requires consideration of audiologic and psychosocial factors. The social isolation associated with acquired hearing loss in elderly individuals¹⁴⁴ is accompanied by a significant decline in quality of life and an increase in emotional handicap.¹⁴⁵ The rehabilitation of hearing loss is an important goal in this vulnerable population, providing functional and psychologic contributions to quality of life.

Age-related degeneration of the spiral ganglion ^146,¹⁴⁷ and progressive central auditory dysfunction^148,¹⁴⁹ raise potential concerns about the efficacy of cochlear prostheses in the elderly. Comparable gains in speech understanding have been reported for elderly and younger groups of implant recipients,¹⁵⁰ but the implications of these functional gains on the quality of life of older adults have not been well characterized. The determination of auditory efficacy and quality of life is crucial to any cost-benefit analysis in elderly patients, and may help guide clinical resource allocation, particularly in light of the high costs associated with cochlear implantation as a nonlifesaving intervention.

Reports of quality of life gains in elderly patients with cochlear implants have been favorable,¹⁵¹^–¹⁵³ but are based on questionnaires that are difficult to correlate with function and cost-utility. Francis and colleagues¹⁵¹ evaluated 47 patients with multichannel cochlear implants, 50 to 80 years old, who completed the Ontario Health Utilities Index Mark 3 (HUI3) survey and a quality-of-life survey. This study assessed preimplantation and postimplantation (6 months and 1 year after implantation) responses to questions related to device use and quality of life. A significant mean gain occurred in health utility of 0.24 (SD 0.33) associated with cochlear implantation (P < .0001) (Fig. 160-7). Improvements in hearing and emotional health attributes were primarily responsible for this increase in health-related quality-of-life measure. A significant increase occurred in speech perception scores at 6 months after surgery (P < .0001 for Central Institute for the Deaf sentence and monosyllabic word tests), and there was a strong correlation between the magnitude of health utility gains and postoperative enhancement of speech perception (r = 0.45, P < .05). Speech perception gain was also correlated with improvements in emotional status and the hours of daily implant use. The authors concluded that cochlear implantation has a statistically significant and cost-effective impact on the quality of life of older deaf patients.

Figure 160-7. Mean monosyllabic word scores obtained in older adult subjects with postlingual hearing impairment just before cochlear implantation (CI) and at 6 and 12 months afterward (error bar = 1 SE). Monosyllabic word scores, which are generally considered one of the most difficult tests of speech perception, clearly increase during the first year after CI.

Quality-of-Life Studies in Children

Published cost-utility analyses of the cochlear implant in children have been limited by using either health utilities obtained from adult patients ^19,^139,¹⁵⁴ or hypothetically estimated utilities of a deaf child.¹⁵⁵^–¹⁵⁸ These studies yielded cost-utility ratios that spread over a wide range ($3141 to $25,450/QALY). Utility assessments derived from adult patient surveys may not capture the impact of issues unique to childhood deafness.³³ To address this issue more rigorously, Cheng and coworkers¹³⁷ surveyed parents of a cohort of 78 children (average age 7.4 years, with 1.9 years of cochlear implant use) who received multichannel implants at the Johns Hopkins Hospital to determine direct and total cost to society per QALY. Parents of profoundly deaf children (n = 48) awaiting cochlear implantation served as a comparison group to assess the validity of recall. Using the Time-Trade-Off (TTO), Visual Analog Scale (VAS), and HUI3, parents rated their child’s health state “now,” “immediately before,” and “1 year before” the cochlear implant. Mean VAS scores increased 0.27 on a scale of 0 to 1 (from 0.59 to 0.86), TTO scores increased 0.22 (from 0.75 to 0.97), and HUI scores increased 0.39 (from 0.25 to 0.64) (Fig. 160-8). Discounted direct medical costs were $60,228, yielding cost-utility ratios of $9029/QALY using the TTO, $7500/QALY using the VAS, and $5197/QALY using the HUI3. Including indirect costs, such as reduced educational expenses, the cochlear implant yielded a calculated net savings of $53,198 per child. Based on assessments of this cohort from a single center, childhood cochlear implantation produces a positive impact on quality of life at reasonable direct costs and results in societal savings.

Figure 160-8. Retrospective health utility scores from parents of children with cochlear implants. Three different methods of assessing health utility scores are shown. The mean change in utility (postintervention—preintervention scores) was 0.27 for the visual analog scale, 0.22 for the time-trade-off instrument, and 0.39 for the health utilities index. The error bars on the side of each graph show mean scores with 95% confidence intervals.

The educational resource matrix used by Francis ¹³⁵ and Koch¹³⁶ and their colleagues offers a basis for assessing overall cost-benefit ratios of the cochlear implant in children. Although educational costs for all implanted students remain static or initially increased, ultimate achievement of educational independence for most implanted children produces net savings that range from $30,000 to $100,000 per child, including the costs associated with initial cochlear implantation and postoperative rehabilitation. Language-related and education-related outcomes in children with cochlear implants have been supplemented with parental perspectives of quality-of-life effects to yield cost-utility ratings.^137,¹⁵⁴ Despite conservative assumptions, results show that cochlear implantation is, relative to other medical and surgical interventions, highly cost-effective in profoundly hearing-impaired young children.

Auditory Rehabilitation after Cochlear Implantation

The uniqueness of the listening experience enabled by a cochlear implant is underscored by qualitative differences in how sound perception is elicited compared with other strategies of auditory rehabilitation. A hearing aid filters, amplifies, and compresses the acoustic signal, delivering a processed signal to the cochlea for transduction. In contrast, a cochlear implant receives, processes, and transmits acoustic information by generating electric fields. Electric hearing bypasses nonfunctional cochlear transducers by directly depolarizing auditory nerve fibers. Implant systems convey an electric code based in selected features of speech that are crucial to phoneme and word understanding in normal listeners, without the advantages of signal preparation provided by cochlear mechanisms of sound processing that render complex sounds listenable and discriminable. The listening experience with the cochlear implant also differs from normal audition in the timing of when that experience begins.

Either through a process of learning in the early, formative years in children, or by virtue of “auditory memory” in adults, capabilities for meaningful listening develop for most implant recipients. A central clinical question relates to the potential benefit to be derived from dedicated sensory training, commonly referred to as “auditory training.” Can such training enable a cochlear implant user to apply latent skills and adaptive strategies to listening tasks that offset deprivation effects and the limitations of cochlear implant listening to capitalize on the device capabilities?

Exposure to conversational speech likely provides insight otherwise unavailable. Language learning may be too complex to be acquired using didactic methods alone. Consistent, frequent exposure may offer the greatest prospects of refining oral language skills. Through tracking the temporal, spectral, and intensity parameters of sound, the cochlear implant provides cues of voicing and articulation patterns that are not visually detectable. For deaf children who experience difficulty in developing their language skills, the possibilities afforded by early implantation, before the onset of changes consequent to deafferentation, seem to be substantial. The best method of achieving such outcomes are yet to be determined, however.

Efficacy of Auditory Training in Cochlear Implant Rehabilitation

Auditory training that provides real-world utility to restored audition in implant recipients is necessarily highly individualized. That is, the goals for a patient’s auditory, speech, language, and cognitive development rely on a host of influences unique to the individual. Because of the need for such an individualized approach, studies of treatment efficacy of auditory training with high internal validity are difficult to construct. Carney and Moeller ¹⁵⁹ noted that earlier efficacy studies target specific treatment areas of perceptual skill development, language development, speech production, academic performance, and social-emotional growth. Treatment goals within various treatment areas often vary, limiting the ability to assess the impact within any single category.

Prior studies have systematically assessed the development of speech perception with training in implant listeners. Watson ¹⁶⁰ noted that studies of the perception of complex nonspeech sounds have shown that individual parts of spectral-temporal waveforms can become more salient through selective training. One consequence of training is that the same sound can be perceived quite differently, depending on earlier experience as it affects a listener’s expectancy and the psychologic mind-set brought to the task. The time course of learning to identify initially unfamiliar speech sounds by normal-hearing listeners extends through months, possibly even years, before reaching a stable level of performance. If implant users are required to learn to interpret sounds as unfamiliar to them as the nonspeech sounds used in research are to normal-hearing listeners, a similar lengthy experience may be required to reach a plateau of maximum performance. Why this has not been the case in some clinical studies is a puzzle.

Watson ¹⁶⁰ offered an explanation in that speech perception may depend heavily on abilities other than sensory acuity or tonal resolution. Studies of individual differences in auditory temporal and spectral acuity have not shown strong correlations between individual differences in those abilities and individual differences in speech perception. It is argued that one way to interpret this observation is that differences in the ability to hear speech (as by two hearing-impaired listeners with the same audiogram) may be the result of differences in the way in which central pathways generate the ability to infer an original stimulus from its fragments.

Dawson and Clark ¹⁶¹ tested whether the ability to use place-coded vowel formant information would be subject to training effects in a group of congenitally deafened patients with limited speech perception ability. They investigated the relationship between electrode position difference limens and vowel recognition. Young subjects were assessed with synthesized versions of the words “hid,” “head,” “had,” “hud,” “hod,” and “hood.” Performance during a nontraining period was compared with the change in performance after 10 training sessions. Two of four subjects showed significant gains, and improvements were consistent with their electrode discrimination ability. Difference limens ranged from one to three electrodes for these patients, and for two other patients who showed minimal to no improvements. Minimal gains shown by one subject could be partly explained by poorer apical electrode position difference limen. The authors concluded that significant gains in vowel perception occurred after training, and suggested the need for children to continue prolonged aural rehabilitation for a period after implantation. Despite intensive efforts, minimal improvements can sometimes occur, however, and such limited success is not always accounted for by limitations at the level of the auditory periphery.

Svirsky and coworkers ¹⁶² examined two possible reasons underlying longitudinal improvements in vowel identification by cochlear implant users: improved labeling of vowel sounds and improved electrode discrimination. Improvements in vowel identification were attributed to improved labeling, suggesting cortical learning effects were responsible for the observed changes, as opposed to enhanced electrode discrimination.

Rehabilitation in Adults with Cochlear Implants

After implant activation, adult users must adjust to the novel signals transmitted by the speech processor. Recipients must learn to associate electrically elicited sound patterns with perceptions that were previously meaningful sound sensations. Rehabilitative needs differ in implant recipients depending on their auditory experience before the onset of deafness. For a prelinguistically deafened implant recipient, auditory and speech (articulation) training are crucial in facilitating communication change. For a postlinguistically deafened patient, auditory training often focuses on more complex listening skills—understanding speech in noise, telephone use, and music appreciation.¹⁶³

Auditory Training in Children with Cochlear Implants

Programs of auditory training in children with implants are often organized with a hierarchic approach by which the child learns to associate meaning with unfamiliar and possibly unnatural sounds.^122,¹⁶⁴ After showing awareness of sounds (detection), the child is taught to determine whether sounds are the same or different (discrimination), to recognize sounds and to associate meaning with them (identification), and to respond appropriately in verbal discourse (comprehension). Expressively, the child learns to imitate phonemes and syllables and to coarticulate these sounds to produce progressively more difficult words and phrases. Imitation or approximation of speech sounds and words is a strategy used for developing an “auditory feedback loop”—the interrelated function of perception of sound and production of speech. Functional use of spoken language depends on the child’s ability to produce meaningful linguistic utterances spontaneously. This process begins with a single word and progresses through sequential stages to complex phrases and entire stories.¹⁶⁵ Boothroyd¹⁶⁶ stressed the need for flexibility in guidelines for therapy sessions, noting that “the structure needs to exist in the mind of the teacher, and not be so obvious in the activities done with the child.”

Boothroyd and colleagues ¹⁶⁷ provided a model of auditory development that highlights the time course of development and identifies component skills that are crucial to effective auditory perception in children. They defined auditory perception as the interpretation of sensory evidence that is derived from sound and is reflective of objects and events that caused the sound. Similar to other perceptual events, auditory perception involves not only sensory evidence, but also contextual evidence, prior knowledge, memory, attention, and processing skills. Auditory speech perception is special because the events to be perceived are those of language. Similarly, the listener’s knowledge base and processing skills must include those related to language in general and to spoken language in particular.

The normal auditory system is complete and functional at birth, but myelination continues for several years in the higher auditory pathways. Correspondingly, infants display increasingly sophisticated discrimination and recognition ability. Psychoacoustic performance does not reach adult levels for several years, however. Infants at 6 months of age show the beginnings of phonemic classification. Their capacity of performance improves during childhood, including phonetic contrast perception, phoneme recognition, perception of speech in noise, selective attention, and the use of linguistic context. Because experience plays a key role in the development of the knowledge and skills required for auditory perception in general, and for auditory speech perception in particular, intensifying that experience in hearing loss and with prosthetic devices is theoretically attractive.

Boothroyd and colleagues ¹⁶⁷ noted that it is tempting to assume that the sensory evidence available to a developing child is determined only by the functional integrity of the peripheral auditory system, independent of auditory experience. Basic science investigations document the influence of auditory experience on the organization of auditory pathways,¹⁶⁸ however, and observe that better organization through experience could increase the sensory evidence made available from patterns of neural excitation produced in the cochlea.

Cochlear implants provide profoundly deaf children with a level of hearing sensitivity that enables them to perceive most of the sounds of spoken language, even when presented at low levels of intensity. Rehabilitative practices are designed to build on this level of sound awareness. In the case of a child who developed an audition-based language system before the onset of deafness, the cochlear implant restores access to spoken language—in many cases with expanded phonemic access. In the case of children who have never heard or who lost their hearing before the establishment of spoken language, access to sound provided by the cochlear implant initially lacks meaningful associations.

Current cochlear implant technology also provides the potential for deaf children to make use of generalization and incidental learning. Benefits of “hearing” extend well beyond contexts of one-on-one repartees with predictable discourse. Age of onset, degree of hearing loss, and amplification history ⁴⁷ determine the quantity and quality of auditory stimulation received before implantation and readiness to interpret acoustic information. A child experienced in using residual hearing from an early age through amplification is likely to adapt to the sounds provided by the implant more quickly than a child with limited experience in listening.¹⁶⁷ The close scrutiny afforded by regular interaction with an auditory training therapist allows for the early detection of either the need for device reprogramming or failure of components of the implant system.

Components of auditory training in children with cochlear implants are designed to foster the development of auditory and speech skills in a manner that simulates a hearing child’s acquisition of spoken language, while addressing remedial needs that arise as a consequence of auditory deprivation during early development.¹⁶⁹ Rehabilitative strategies related to auditory, speech, and language skills should seek to achieve overall communicative competence.⁵⁰ Ideally, rehabilitative strategies do not teach specific, isolated auditory, speech, or language subskills. Because subskills are only a means to an end that is multimodal communicative competence, training in any one individual subskill should not be given too much weight. Programs are most effective when they take an integrated approach to rehabilitation and avoid rote, drill-oriented approaches.

Maintenance of the Device

An important role in developing auditory skills and using a cochlear implant successfully is maintenance of the device itself.^155,¹⁵⁶ This maintenance includes keeping all external parts in good functioning order, and working with an audiologist who specializes in cochlear implants on a regularly scheduled basis for device programming. In most cochlear implant centers, the audiologist serves as the case manager for the patient during the cochlear implant candidacy process and postimplantation.

Programming the device requires software and hardware from the cochlear implant manufacturer. For an adult patient, programming the cochlear implant involves numerous perception judgments, such as threshold of hearing, loudness level, loudness balancing, and in some cases pitch ranking. The patient’s hearing history can determine the ease or difficulty of these tasks. Other factors, such as tinnitus, can come into consideration when establishing threshold levels of hearing with an electric stimulus. These measurements are necessary to program a patient’s dynamic range of hearing with the cochlear implant. These settings are individual and can vary from patient to patient. The program that is saved to the external components is referred to as the cochlear implant map. Changes in the stimulus levels are most frequently seen in the initial stages of activation of the device. Many appointments are involved in the activation process to keep up with the physiologic changes involved with an individual learning to hear with the electric input. Through time, the stimulus levels become more stable, and primarily fine-tuning adjustments are made. Little research is available to explain the physiologic changes that induce needed map changes. Anecdotal reports are available that also suggest various program changes are needed when the patient is undergoing hormonal changes, such as pregnancy, puberty, or menopause.

If the patient is unable to participate in the judgments needed to create a cochlear implant map, some objective measures may be used. Cochlear implant manufacturers have created software that can measure an electrically evoked compound action potential through the cochlear implant: Neural Response Telemetry (NRT), by the Cochlear Corporation of Englewood, Colorado (manufacturer of the N24 device), and Neural Response Imaging (NRI), by the Advanced Bionics Corporation of Sylmar, California (manufacturer of the Clarion/Hi-Res devices). NRT measures are found at levels between threshold and maximal comfort in an individual’s map. Limitations exist when using these measurements.^170,¹⁷¹ Although direct nerve responses seem to have value in some populations, behavioral testing is the tried and true method of programming.

Another objective measurement that has been previously used in device programming is electric acoustic reflex thresholds. Studies have found that the electric acoustic reflex threshold highly correlates with comfort levels on a cochlear implant map.^172,¹⁷³ These measurements are not present in all patients, however, so this option may not always be available. If the reflex is measurable, this can provide valuable information for the audiologist when programming a child. Some children have high tolerance levels for the electric stimulus and do not react negatively if the map is created using inappropriately high levels. If the cochlear implant program is too loud, it can prevent the child from developing auditory skills or responding appropriately.

Audiograms may also be used to check the validity of a cochlear implant map. Using the audiogram has limitations, however, when determining the integrity of a cochlear implant program. The audiogram is going to show the patient’s responses to the perception of soft stimuli. It does not tell you, however, whether the program is at an appropriate comfort level, or whether the sound quality of the map is good. Most cochlear implant audiograms are in the 20- to 30-dB range. It is possible to have a good audiogram with inappropriate map settings in the external device. A strength of the audiogram is that it can flag equipment malfunction or gross changes needed in the cochlear implant settings.

Intensive follow-up is required for successful outcomes after cochlear implantation. The adult cochlear implant patient should have his or her external devices reprogrammed at least annually. Pediatric patients should, at a minimum, come on a biannual basis. Many children are seen more frequently than a twice a year if any questions arise on how their listening skills are developing, and to ensure that their devices are programmed appropriately. Regularly scheduled program checks also offer an opportunity for the audiologist to track the development of the patient’s speech understanding scores using the MSTB protocol explained previously. Conducting speech perception measures at regular intervals can provide the cochlear implant audiologist or therapist with valuable information on what the patient is hearing and understanding. This information can be used to change the patient’s map or as an indication of where to focus therapy goals. Also, if the patient reports a sudden change in performance, this change can be documented by showing a decrease in speech perception abilities. This documentation validates the patient’s concerns and assists the audiologist and therapist to help return the patient to baseline functioning.

The cochlear implant should not be considered a “fix” for severe to profound hearing loss. This device requires intensive rehabilitation to use it effectively and requires regular follow-up and maintenance. Although the learning process with the cochlear implant seems complex and unpredictable, the cochlear implant can provide an opportunity for deaf individuals to hear sounds that would never be possible with conventional amplification. This is especially true for deaf children, who can use the cochlear implant as a tool for receptive and expressive oral speech abilities and, most importantly, language learning.

Educating Children with Cochlear Implants

Deaf education has long been concerned with the necessity of overcoming the devastating effect profound deafness has on language acquisition and on educational attainments. Normally hearing children come to education and the development of literacy and numeracy skills with language already acquired through the channel of hearing in interaction with their care providers. For children deaf from birth, this normal process is disrupted with consequent effects on language acquisition. Deaf education is concerned not only with the processes of educational attainments of literacy and numeracy, but also with the processes of linguistic development and how to overcome the problem of lack of hearing in the normal communicative development.

The two major questions that have challenged educators for years have been which communication method to use (oral or sign language), and where to educate children (in special or mainstream schools). Visual means of communication were promoted, with sign language being seen as the solution by some, and oral language using visual support of lip-reading and other clues as the way forward. In 1880, the Milan conference on deaf education promulgated the opinion that oral language was “superior” to that of sign language. This statement, at a time when there was little amplification available, began the predominance of oralism throughout the world, and a polarization of views between individuals who believed that all deaf children should communicate by spoken language alone, and individuals who believed that all deaf children should communicate by sign language.

Although the oral view was held strongly in the 19th century and first half of the 20th century, reports of poor linguistic and educational attainments and speech intelligibility of deaf children began to challenge it. The increasing voice of the deaf community, wanting recognition of its own language and culture, also began to be heard. Signed methods of communication were increasingly introduced to educational systems in many countries, often taking the form of total, or simultaneous, communication, where spoken language is used with signed support. This method does not use the grammar of sign language, however, and in the 1980s interest grew in the use of sign bilingualism, where the languages of the deaf community and the hearing community are used to varying degrees and emphases. In the United States, the term “bi-bi” is often used to describe bilingual and bicultural approaches. Although terminology may vary, communication approaches may be grouped into three broad categories:

• Oral/aural—spoken language alone

• Use of speech and sign simultaneously (total communication)

• Bilingualism

There are subcategories within each category; oral communication methods include natural oralism, the use of cued speech, and auditory verbal approaches. These subcategories make comparison of the effectiveness of differing communication choices complex, and make the appropriate communication choices challenging for parents.

Another major choice for parents pertains to the setting in which their deaf child should be educated. Historically, deaf children were educated in special schools for the deaf. These schools were often residential and in remote areas, requiring children to leave home and obtain their education away from their families. Large schools for the deaf were established in many countries in the 19th century, and deaf culture and language thrived in these institutions. During the second half of the 20th century, there was an increasing trend for children with any disability to be educated in mainstream schools with appropriate support. For deaf children, the development of more effective hearing aids and the provision of FM systems facilitated the greater possibility of participation in mainstream education.

The closure of many schools for the deaf has been a worldwide phenomenon, which may be seen by the deaf community as a threat to their culture and language. With more children in mainstream schools, a reduction in special schools may also mean greater difficulty in providing specialist educational support to deaf children, and greater difficulty in accessing individuals working with deaf children in mainstream schools for continuing professional development and attaining the knowledge and expertise they need.

The options for educational placement today are the following:

• A school for the deaf (residential or day)

• A unit or resource base in a mainstream school (with varying degrees of integration into the mainstream school)

• A mainstream school (with varying degrees of support in quality and quantity)

These situations are not mutually exclusive, but overlap to a large degree, with wide variations in practice, particularly in degree of support. This overlap makes comparisons about educational independence in varying educational settings complex, and comparing the effectiveness of differing educational settings complex. Francis and colleagues ¹³⁵ produced a useful matrix of educational resource use, illustrating the continuum of support; a child in a mainstream school with full-time support in class may have less educational independence than a child in a class of 10 in a special school.

Historically, the education of deaf children has been the subject of great controversy, often fed by rhetoric rather than fact, and with few data about the comparative efficacy of various alternatives, or information about making such important choices for parents. Into this already controversial area, the advent of cochlear implantation has added another dimension.

Advent of Cochlear Implantation

The advent of cochlear implantation was hoped to ameliorate the educational challenges produced by profound deafness.⁸⁰ In providing useful hearing across the speech frequencies, cochlear implantation facilitates the development of early communication skills and spoken language through interaction with care providers. Early reports of encouraging levels of spoken language perception and production led many authors to predict that mainstream education would be the likelihood for most profoundly deaf children. The success of cochlear implantation has often been measured in terms of access to mainstream education, not least because it has been seen as a means of measuring cost-benefit from cochlear implantation.^135,¹⁵⁴ Children with implants are attending mainstream schools in greater numbers after implantation,¹⁷⁴ and this has been thought to be associated with potential savings in educational costs.¹⁵⁴

What are the needs of children with implants, and are they different from the needs of users of traditional hearing aids? Children with implants need the implant system working well and worn consistently, good listening conditions, and good communication opportunities. These needs are not so different from the needs of hearing aid wearers. What cochlear implants have done is enable profoundly deaf children to function as moderately deaf—and many with a unilateral loss, despite the trend to bilateral implantation. Cochlear implants provide useful hearing to enable profoundly deaf children to acquire language through hearing,¹⁶⁹ to hear all the grammatical features of speech, and to develop wholly intelligible speech. Cochlear implants require complex technology, which requires a surgical procedure and long-term maintenance. How to ensure that children with implants obtain the maximum benefit from this technology remains a challenge.

It has long been recognized that the long-term management of deaf children with implants is in the hands of educators, and there is a major need for educators responsible for the children on a daily basis to have training and regular updates on this complex technology and the expectations they can have. In a survey of parents, community-based implant professionals, and implant professionals in Europe,¹⁷⁵ the most common thread in the responses was the need for long-term support in education for the implant system and for educational services to become more flexible in meeting the needs of this growing group of children. Parents expressed great frustration that their children did not receive the support they needed particularly as they went to secondary or high school, and frustration that there were not greater links between the implant centers and the local educational services. A survey of European teachers of the deaf showed that they were highly interested in receiving information and training about cochlear implants.¹⁷⁶

To be successful in mainstream education, it must be ensured that the classroom situation is appropriate, with good acoustics, and that the technology is successfully managed, with high expectations of its use. We know the educational implications of a unilateral or moderate hearing loss in the busy mainstream classroom environment ^177,¹⁷⁸; children would mishear or misunderstand in noise and not follow the fast-moving discourse around the classroom. For some children, implants may work too well: their speech intelligibility may be such that they appear as normally hearing children, and their needs may be overlooked, and for the children themselves it is difficult to articulate their needs. In such situations, misunderstandings would continue, and children would be unlikely to realize their academic potential. For other children, the implant may not have provided the outcomes expected; the range of outcomes from implantation is large. For these children, an auditory processing disorder or a language learning difficulty may be present, which affects the development of spoken language. The educational needs of these children may not be met in mainstream provision, as had been predicted.

Educational Outcomes

With regard to these educational decisions that parents make for their children, there is evidence that cochlear implantation has had an influence. More children with cochlear implants are going to mainstream schools than to schools for the deaf compared with a group of profoundly deaf children with hearing aids of the same age.¹⁷⁴ These were children 5 to 7 years old; Thoutenhoofd¹⁷⁹ did not find such a trend long-term toward mainstream placement, and there is anecdotal evidence that children with implants are findin g challenges in managing in the secondary or high school environment. Geers and colleagues¹⁸⁰ also found a trend toward mainstream education, but again this was in children at the primary stage.

With regard to communication mode and choices of communication after implantation, there is varying evidence of the influence of oral and signing environments. On the whole, the trend is to support the use of oral input,¹⁸⁰ but the context in which this is best provided in the long-term is still debated, and the situation is complex. Archbold and colleagues¹⁸¹ showed that the outcomes in terms of speech perception and production 3 years after implantation were not different in children who had begun with some form of signed input and changed to oral, and children who had used oral communication only. Further study showed that children implanted before age 3 change from using signed communication to oral communication,¹⁸² and children implanted at a younger age change communication mode faster.⁶⁸ There is evidence that although young people with implants develop intelligible spoken language, they also value the use of sign language, or signed support.¹⁸³ If children are to develop spoken language, however, they need to be in an educational environment that values it and promotes its use.

With regard to educational attainments, Stacey and coworkers ¹⁸⁴ and Thoutenhoofd¹⁷⁹ showed that children with cochlear implants had improved educational attainments compared with children with hearing aids. Increasing evidence is showing that children with implants have better reading skills than comparative groups with hearing aids,¹⁸⁵ and that children implanted younger are continuing to read at improved rates.¹⁸⁶ In providing access to the grammatical features of spoken language through hearing, cochlear implants have enabled profoundly deaf children to have a greater awareness than previously of the phonology of language before coming to the written word. Spencer and Marschark¹⁸⁷ stated, “Spoken language development of deaf children may be more possible today than ever before. We are poised on a threshold of what often seem like unlimited possibilities.” This statement reflects the ways in which new hearing technologies, and cochlear implantation in particular, have transformed educational opportunities for deaf children.

Recent Posts

Meta

Categories

Search Engine

Cochlear Implants: Results, Outcomes, Rehabilitation, and Education

Results of Implantation

Factors Related to the Measurement of Auditory Performance

Tests of Implant Performance