Teresa A. Zwolan

The age at which young deaf children receive cochlear implants and their vocabulary and speech-production growth: is there an added value for early implantation?

Objective: The age at which a child receives a cochlear implant seems to be one of the more important predictors of his or her speech and language outcomes. However, understanding the association between age at implantation and child outcomes is complex because a child’s age, length of device use, and age at implantation are highly related. In this study, we investigate whether there is an added value to earlier implantation or whether advantages observed in child outcomes are primarily attributable to longer device use at any given age. Design: Using hierarchical linear modeling, we examined latent-growth curves for 100 children who had received their implants when they were between 1 and 10 yr of age, had used oral communication, and had used their devices for between 1 and 12 yr. Children were divided into four groups based on age at implantation: between 1 and 2.5 yr, between 2.6 and 3.5 yr, between 3.6 and 7 yr, and between 7.1 and 10 yr. Results: Investigation of growth curves and rates of growth over time revealed an additional value for earlier implantation over and above advantages attributable to longer length of use at any given age. Children who had received their implants before the age of 2.5 yr had exhibited early bursts of growth in consonant-production accuracy and vocabulary and also had significantly stronger outcomes compared with age peers who had received their implants at later ages. The magnitude of the early burst diminished systematically with increasing age at implantation and was not observed for children who were older than 7 yr at implantation for consonant-production accuracy or for children who were over 3.5 yr old at implantation for vocabulary. The impact of age at implantation on children’s growth curves differed for speech production and vocabulary. Conclusions: There seems to be a substantial benefit for both speech and vocabulary outcomes when children receive their implant before the age of 2.5 yr. This benefit may combine a burst of growth after implantation with the impact of increased length of use at any given age. The added advantage (i.e., burst of growth) diminishes systematically with increasing age at implantation.

Cochlear implant failures and revision.

Objective: To review cases involving implant failure and revision surgery in a large cochlear implant program. Study Design: Retrospective case series. Setting: Cochlear implant program in an academic medical center. Patients: Adults and children who underwent revision cochlear implantation (n = 58). Intervention: Diagnosis and explantation of failed cochlear implants, with subsequent reimplantation. Assessment of implant function and speech perception. Main Outcome Measures: Device type, time from implantation to revision, cause of failure, performance with original implant versus revision, number of electrodes placed, and surgical challenges related to reimplantation. Results: Forty-five patients initially implanted at this program and 13 patients implanted elsewhere underwent revision surgery. The institutional device failure rate was 3.7% and the overall revision rate was 5.1%. Reasons for implant revision included documented internal device failure (46%), scalp flap complications (17%), optimization of electrode placement (13%), unexplained deterioration of performance (12%), technology upgrade (10%), and intratemporal pathology (3%). Revision surgery typically involved only minor anatomic challenges, but five patients required circumodiolar drillout procedures to improve electrode position. Electrode insertion was equal or deeper in 53 of 58 cases. Speech perception ability decreased in only three patients. Conclusions: Management of implant failures and performance of revision surgery are becoming increasingly important in cochlear implant programs. Outcomes are generally excellent. Revision implantation is a safe and appropriate procedure that should be pursued in a timely fashion when patients experience cochlear implant failure.

Comparison of electrode discrimination, pitch ranking, and pitch scaling data in postlingually deafened adult cochlear implant subjects

The goal of this study was to investigate the relationship between variation in electrode site of stimulation and the perceptual dimensions along which such stimuli vary. This information may allow more effective use of electrode place when encoding speech information. To achieve this goal, two procedures which measure pitch in subjects implanted with the Nucleus/Cochlear Corporation multichannel device were performed. Estimates of electrode discriminability that can be obtained from these procedures were compared to a more direct measure of electrode discriminability that was obtained in a previous study [Collins et al., Assoc. Res. Otolaryng. Abstracts, No. 642 (1994)]. In the first task, subjects performed a pitch ranking procedure similar to that used in previous studies [Townshend et al., J. Acoust. Soc. Am. 82, 106-115 (1987); Nelson et al., J. Acoust. Soc. Am. 98, 1987-1999 (1995)]. Estimates of the pitch percept elicited by stimulation of each electrode as well as the discriminability of the electrodes were generated from the data using two different statistical analyses. In the second task, subjects performed a pitch scaling procedure similar to one used in a previous study [Busby et al., J. Acoust. Soc. Am. 95, 2658-2669 (1994)]. Again, two different statistical analyses were performed to generate estimates of the pitch percept corresponding to stimulation of each electrode and to generate estimates of electrode discriminability. In general, the estimates of the relationships between the pitch percepts obtained from the two procedures were not identical. In addition, the estimates of electrode discriminability were not equivalent to the electrode discrimination measures obtained from the same subjects during the previous study. Signal detection theory has been used to model the decision processes required by each of the procedures described above [e.g., Jesteadt and Bilger, J. Acoust. Soc. Am. 55, 1266-1276 (1974)]. However, these models do not predict the differences that were observed between the data sets obtained during this study. An alternate model is proposed which may explain the data obtained from these subjects. This model is based on the assumption that the percept that is elicited by electrical stimulation of an electrode is multidimensional, as opposed to unidimensional in nature. Therefore, the perceived signal is more appropriately modeled using a multidimensional random vector, where each element of the vector represents the perceived value of one of the dimensions of the signal.

Effects of stimulus configuration on psychophysical operating levels and on speech recognition with cochlear implants

Effects of electrode configuration and pulse duration on operating levels and on speech recognition performance were studied in a group of 14 adult postlingually deaf human subjects with Nucleus cochlear implants. The operating levels (based on detection threshold and maximum comfortable loudness levels) for narrowly spaced bipolar (BP) stimulation were found to be about 11 dB higher on average than those for widely spaced bipolar (BP+6) or monopolar (MP1) stimulation. Operating levels for common ground (CG) stimulation fell between those for BP and BP+6; the difference between BP and CG detection thresholds depended on pulse duration. Variation in detection thresholds and maximum comfortable loudness levels across the electrode array (electrodes 1-15) was larger for BP and CG stimulation than for BP+6 or MP1 stimulation, suggesting narrower spread of activation for the BP and CG configurations despite the higher current levels. Speech recognition performance was tested using experimental processor configurations. Among the experimental electrode configurations tested (BP, CG, and BP+6), the highest speech recognition scores were obtained with the BP+6 configuration in many subjects. Effects of pulse duration on speech recognition were less consistent and usually smaller than the effects of electrode configuration. The results indicate that electrode configuration is an important variable determining speech recognition performance and suggest that restriction of the size of neural population activated by individual channels of the prosthesis is not necessarily advantageous.

The influence of age at implantation on performance with a cochlear implant in children.

Objective This study involved the assessment of speech recognition abilities as a function of age at implantation and length of cochlear implant use in children who received the Nucleus CI22M cochlear implant. Study Design Two separate analyses were performed. The first analysis involved the assessment of speech recognition performance as a function of length of time with a cochlear implant in 48 patients evaluated at 7 years of age. The second analysis involved the assessment of speech recognition performance as a function of age at implantation in 53 patients evaluated 36 months after implantation. Patients were divided into four groups based on length of implant use or age at implantation, and the results were analyzed by a repeated-measures analysis of variance. Setting This study was carried out at a tertiary academic medical center. Patients Patients consisted of children implanted with a Nucleus Multi Channel cochlear implant programmed with the SPEAK encoding strategy. Their ages at the time of evaluation ranged from 5.5 to 7.8 years. Their ages at implantation ranged from 2.4 to 14.5 years. Interventions All patients received a Nucleus Multi Channel cochlear implant programmed with the SPEAK encoding strategy. Word and sentence recognition tests were administered at various ages and at several postimplantation intervals. Main Outcome Measures Performance as a function of length of cochlear implant use and as a function of age at implantation. Results Patients performed significantly better as length of cochlear implant use increased and age at implantation decreased. When patients were tested at a fixed postimplantation time interval (36 months), there was an overall trend for patients who received the implant at a younger age to perform better in spite of being younger at the time of evaluation. However, these effects were not statistically significant for all speech recognition tests that were administered. Conclusions These results confirm previous findings indicating continued improvement of speech recognition with time in implanted children. Furthermore, the results support the concept of the advantage of a younger age at implantation.

Implantation of the malformed cochlea

Objective This study assesses the results of cochlear implantation in children with cochlear malformations. Study Design Retrospective, matched-pairs analysis of prospectively collected data. Setting University-based regional cochlear implant center. Patients Seventeen children with osseous cochlear malformations who had undergone implantation were matched and compared with a group of children with normal cochleae who had undergone implantation. Interventions All subjects received a multichannel cochlear implant and habilitation. Main Outcome Measures All subjects were tested with the Early Speech Perception test, and the Glendonald Auditory Speech Perception tests for words and sentences. Patients were classified in a standardized speech perception category based on performance on the Early Speech Perception test. Results All subjects demonstrated improving performance on all measures of speech perception over time. Overall, the two groups showed no statistically significant differences in performance at 6 and 24 months. However, subjects with malformed cochleae evidenced slower rates of improvement than did their matched control subjects. Subjects with more severe malformations demonstrated poorer performance, but this may have been attributable to preoperative factors rather than to implant performance. Conclusions Children with radiographic cochlear malformations benefit from cochlear implantation with multichannel devices. They ultimately perform as well as their matched counterparts with normal cochleae, although they may improve more slowly over time.

Effects of phase duration on detection of electrical stimulation of the human cochlea

Detection thresholds for biphasic symmetric pulses were measured in fourteen human subjects implanted with the Cochlear Corporation Nucleus 22 Implant. The effects of phase duration on thresholds were studied using single pulses, and 500 ms pulse trains at 100 pps. Psychophysical detection thresholds decreased as a function of phase duration with a change in slope at approximately 0.5 ms/phase. Mean single-pulse and pulse-train slopes were -3.60 and -4.25 dB/doubling of phase duration for pulse durations of less than about 0.5 ms/phase. For pulse durations greater than 0.5 ms/phase, mean slopes were -5.71 and -7.54 dB/doubling for single pulses and pulse trains, respectively. Thresholds for pulse trains decreased as a function of stimulus duration for durations up to at least 300 ms, with the rate of decrease being dependent on the phase duration of the pulse. Effects of stimulus duration were greater for longer phase duration signals. We hypothesize that the longer phase duration pulses activate multiple spikes in a single fiber and/or more effective patterns of spikes across fibers, which may explain why slopes of psychophysical threshold functions are steeper than those of functions for single auditory nerve fibers for longer duration pulses. Thresholds were compared to respective speech perception scores (CID sentences) since thresholds for long phase duration signals have been shown previously to be correlated with nerve survival patterns, and nerve survival patterns may affect speech perception. Correlation coefficients ranged from -0.59 to -0.81, depending on stimulus parameters and subject selection.

Effects of stimulus level on electrode-place discrimination in human subjects with cochlear implants

Effects of stimulus level on discrimination of one stimulation site from another were examined in 15 human subjects with Nucleus-22 cochlear implant systems. Bipolar stimulation was used in all cases with electrodes in the bipolar pair separated by 1.5 mm (center to center). Subjects were first tested at a medium loudness level, using an adaptive tracking procedure, to determine the regions of the electrode array where electrode-place discrimination was best and the regions where it was poorest. Electrode-place discrimination was then tested at three regions distributed throughout the array, which included the regions of best and poorest discrimination. At each region, electrode-place discrimination was tested at three levels: 25%, 50%, and 75% of the dynamic range. For each of these nine conditions (3 sites x 3 levels), the test-electrode pairs were loudness balanced with the reference-electrode pairs. A two-interval forced-choice same-different procedure was then used to determine discriminability of the reference-electrode pair from the nearest, apical, test-electrode pair. If P(C)max was <0.707 at all three levels, additional testing was done using the next, more apical, electrode pair as the test-electrode pair. A tendency toward better discrimination at more apical regions of the array was observed. Electrode pairs with poor discrimination typically had smaller dynamic ranges than those with good discrimination. There was a weak tendency toward better discrimination at higher levels of stimulation. However, effects of level on electrode-place discrimination were less pronounced and less consistent than previously observed effects of level on temporal discriminations. These results suggest interactions between current spread and the condition of the implanted cochlea as underlying mechanisms.

Children with cochlear implants who live in monolingual and bilingual homes.

Objective: To determine if exposure to a second language impacts the ability of children with cochlear implants to develop spoken English skills. Study Design: Matched-pairs comparison of postoperative speech perception and speech/language data of children from monolingual and bilingual homes with cochlear implants. Setting: Tertiary medical facility. Subjects: Twelve matched pairs of children with unilateral cochlear implants who reside in monolingual or in bilingual homes. Pairs were matched for age of implantation, cochlear anatomy, educational setting, and device type. All subjects received their implant before the age of 6 years. Intervention: Subjects participated in routine speech perception and speech and language assessments at various postimplantation time intervals. Main Outcome Measures: Matched-pairs t tests and mixed-model analyses were used to evaluate and compare scores obtained by the 2 groups on the Peabody Picture Vocabulary Test, The MacArthur-Bates Communicative Development Inventory: Words and Gestures, The Oral and Written Language Scales, The Infant-Toddler Meaningful Auditory Integration Scale, and the Student Oral Language Observation Matrix. Results: No significant differences were found between the scores of children living in bilingual homes when compared with the scores obtained by children living in monolingual homes at any interval tested. Conclusion: This study supports the belief that exposure to a second language at home does not impair primary language acquisition for some young children with cochlear implants. The study suggests that some children with cochlear implants can learn multiple spoken languages and that parents of such children do not need to avoid using a minority language with their child who has a cochlear implant.

Cochlear implantation in prelingually deaf children with ossified cochleae.

Objective To evaluate the effects that degree of cochlear ossification has on performance of prelingually deafened children who receive cochlear implants. Study Design A matched-pairs analysis comparing speech perception results obtained 6 and 24 months after implant by children with ossified and nonossified cochleae. Additionally, long-term performance was evaluated in patients with follow-up periods longer than 24 months. Comparisons were also performed within the ossified cochleae group to determine if degree of cochlear ossification and surgical technique affected outcome with the cochlear implant. Setting Large cochlear implant program in an academic tertiary care medical center. Patients Twenty-one pairs of prelingually deaf children with and without cochlear ossification. Meningitis was the etiology of hearing loss in children with ossified cochleae. The control group had nonmeningitic etiology for the hearing loss. Interventions Multichannel cochlear implantation and routine postoperative auditory rehabilitation and performance evaluation. Main Outcome Measures Speech perception category ratings based on scores obtained on a battery of closed- and open-set speech recognition tests 6 and 24 months after implant. Longer follow-up period is also reported. Results As a group, children with cochlear ossification showed significant improvement in their speech perception abilities 6 and 24 months after implant. Children with cochlear ossification performed at a significantly lower speech perception category than a group of matched controls with nonossified cochleae at both the 6- and 24-month postimplant intervals. With longer implant use, open-set speech recognition was possible in some children with ossification. Within-group analysis of the children with ossified cochleae revealed that degree of ossification and surgical procedure used for implantation did not significantly affect outcome. Conclusions Prelingually deafened children with postmeningitic hearing loss and ossified cochleae receive significant benefit from cochlear implants. Their performance is frequently poorer, however, than children with nonossified cochleae.