Calculation of the Faradaic Impedance of the Electrode-Tissue Interface Improves Prediction of Behavioral T/C Levels in Cochlear Implant Patients.

BACKGROUND: Fitting of cochlear implants is a labor-intensive process, and therefore automated fitting procedures are being sought. The objective of this study was to evaluate if decomposition of the complex impedance of the electrode-tissue interface could provide additional parameters that show improved correlation with the behavioral T/C levels. METHODS: A new method for decomposing the complex impedance of the electrode-tissue interface was developed and tested in 18 patients in a prospective study in a tertiary otologic referral center. RESULTS: The averaged near-field Faradaic resistance (RF) calculated in study subjects shows a very strong correlation (R2=0.80) with the behavioral C levels and can be used for automated fitting in most patients. The standard deviation for the T levels and the C levels calculated for each of the electrode contacts in all study subjects is in the range of 10-15 CL and 15-20 CL, respectively. These higher values of the standard deviations are caused by a few outliers who require that additional parameters have to be added to the metric equation, allowing for the automated prediction of the T/C levels. CONCLUSION: A new method for deriving information from the electrode impedance measurements shows excellent correlation of the Faradaic resistance with the behavioral T/C levels in most patients and can be very useful for fitting cochlear implants based on objective measures. Since some patients still show discrepancies between the predicted T/C levels based on the RF calculation, additional parameters have to be added to the metric equation, allowing for automated prediction of the T/C levels.

Earlier intervention leads to better sound localization in children with bilateral cochlear implants.

We present sound localization results from 30 children with bilateral cochlear implants. All children received their implants sequentially, at ages from 6 months to 9 years for the first implant and 1.5-12 years for the second implant, with delays of 10 months to 9 years. Localization was measured in the sound field, with a broadband bell-ring presented from 1 of 9 loudspeakers positioned in the frontal horizontal plane. The majority of the children (63%) were able to localize this signal significantly better than chance level. Mean absolute error scores varied from 9 to 51 degrees (root mean square error scores from 13 to 63 degrees ). The best scores were obtained by children who received their first implant before the age of 2 years and by children who used hearing aids prior to implantation for a period of 18 months or longer. Age at second implantation was important in the group of children who did not use a contralateral hearing aid during the unilateral implant period. Additionally, children who attended a mainstream school had significantly better localization scores than children who attended a school for the deaf. No other child or implantation variables were related to localization performance. Data of parent questionnaires derived from the Speech, Spatial and Qualities of Hearing Scale were significantly correlated with localization performance. This study shows that the sound localization ability of children with bilateral cochlear implants varies across subjects, from near-normal to chance performance, and that stimulation early in life, acoustically or electrically, is important for the development of this capacity.

Sound localization, sound lateralization, and binaural masking level differences in young children with normal hearing.

OBJECTIVES: In this study, procedures for measuring sound localization, sound lateralization, and binaural masking level differences (BMLDs) in young children were developed. Sensitivity for these tasks was assessed in large groups of children between 4 and 9 yr of age to investigate potential developmental trends. DESIGN: Sound localization was measured in the sound field, with a broadband bell-ring presented from one of nine loudspeakers positioned in the frontal horizontal field. A group of 33 children between 4 and 6 yr of age and 5 adults took part in this experiment. Sound lateralization based on interaural time differences was measured with headphones in 49 children between 4 and 9 yr of age and 10 adults. A low-frequency stimulus containing harmonics 2 to 5 from a click train with a rate of 160 Hz was used. In the BMLD test, the same filtered click train was presented diotically or dichotically (phase reversed or time delayed) in a broadband (200 to 1000 Hz) frozen noise to 23 children between 4 and 6 yr of age and 10 adults. For comparison with literature, additional measurements with a 500-Hz sinusoid were administered to adults. All tasks were adapted to the interest and attention span of young children. RESULTS: Children of 5 yr of age did not perform significantly different from adults on the sound localization task, but mean absolute errors were larger for the 4-yr-olds. Also on the BMLD task, 5-yr-old children performed at the adult level, whereas the 4-yr-old children obtained significantly less binaural unmasking compared with the adults. Concerning sound lateralization, a small but significant difference between adults and children existed, but no age effects were apparent in the 4- to 9-yr-old group. Overall, the variation was relatively large in the 4-yr-old group, with some of the children performing at adult level, in all three tasks. CONCLUSIONS: The results of this study show that the modified procedures are suitable for testing children from the age of 4 to 5 yr. Furthermore, it seems that binaural hearing capacities of the 5-yr-olds are similar to those of adults. Several observations led to the hypothesis that the observed age differences between 4-yr-olds and older subjects on localization and BMLD or between those 4- to 9-yr old and adults on lateralization, were attributable to both a development in binaural hearing and to nonauditory factors, such as task comprehension, attention, and testing conditions. It is possible that the developmental process is more obvious and prolonged in other aspects of binaural hearing, which require more dynamic or more central processing.

Bilateral cochlear implants in children: binaural unmasking.

Bilateral cochlear implants (CIs) may offer deaf children a range of advantages compared to unilateral CIs. However, speech perception in noise is mainly facilitated by better-ear effects and much less by interaural comparisons or true 'binaural' hearing. Little is known about the development of the binaural auditory system with CIs provided at a young age. It is possible that, as with adults, binaural sensitivity exists but is not accessed due to technical limitations in electrical stimulation methods. In this paper, we present results on binaural hearing in children with bilateral CIs. Binaural masking level differences (BMLDs) were measured for a 180-degree phase shift in a 125-Hz sinusoid, presented in a 50-Hz-wide noise band and modulating a 1000-pps carrier pulse train. Stimuli were presented to a single electrode in the middle of the electrode array at both ears. Eight children between 6 and 15 years of age participated in this study. Six children had a significantly better detection threshold when the signal was out of phase (dichotic) between two ears than when it was in phase (diotic), with a mean difference (BMLD) of 6.4 dB. The present results show that children with bilateral CIs are sensitive to binaural cues in electrical stimuli, similar to adults, even when implants are provided at a later age and with a longer delay between implantations.

Pitch estimation of a deeply inserted cochlear implant electrode.

In this short communication, we evaluate the place-pitch relation of a newly designed, deeply inserted, cochlear implant electrode. The insertion depths ranged from 471 degrees to 662 degrees. Pitch perception was measured in eight subjects with monopolar stimulation on each electrode contact at intensities of 50% and 80% of the dynamic range. We observed a monotonic reduction of pitch estimate with insertion depth. For about half of the subjects, a flattening of the pitch estimate at the basal end of the electrode was seen, while for the other half, pitch continued to decrease monotonically up to the most apical part of the array. We conclude that deeper insertion could increase pitch range for at least some cochlear implant recipients, and could hence potentially increase group performance.

Outcome of cochlear implantation at different ages from 0 to 6 years.

OBJECTIVE: To evaluate the outcome of cochlear implantation in young children in relation to the age at implantation. STUDY DESIGN: A retrospective longitudinal and cross-sectional analysis of pediatric cochlear implant patients. PATIENTS: All children with congenital deafness who underwent implantation before the age of 6 years (n = 48 for the longitudinal analysis and n = 70 for the cross-sectional analysis) INTERVENTIONS: All children received a multichannel cochlear implant. MAIN OUTCOME MEASURES: Categories of Auditory Performance (CAP) score and integration into the mainstream school system. RESULTS: For all children, the CAP score increased after implantation. Implantation beyond the age of 4 years hardly ever resulted in normal CAP scores or in integration into the mainstream primary school (20 to 30% of cases). Implantation between the age of 2 and 4 years always resulted in normal CAP scores after 3 years with a 66% probability of integration into the primary school. Implantation before the age of 2 years always resulted in immediate normalization of the CAP scores, with a 90% probability of integration into the mainstream kindergarten, well before entrance into the primary school. CONCLUSION: All children with congenital deafness who underwent implantation before the age of 6 years appeared to benefit from the implant. However, these data add evidence to the importance of early implantation (before the age of 2 years). Intervention before the age of 4 years seemed to be critical to avoid irreversible auditory performance losses, and intervention before the age of 2 years seemed to be critical to achieve optimal results.

The use of malleus allografts in ossiculoplasty.

OBJECTIVE: To assess the functional performance of remodeled malleus allografts in a malleus-footplate assembly in terms of hearing results and mid long-term stability. STUDY DESIGN: A retrospective study of 60 consecutive patients who underwent a malleus allograft ossiculoplasty from 1993 until 2000. In all cases the incus and the stapedial arch were missing as the result of cholesteatoma (49), chronic otitis (5), incus necrosis resulting from stapes prosthesis (5), and congenital ossicular malformations (1). In all cases malleus allografts were remodeled to form a malleus-stapes assembly. RESULTS: The audiometric results, using such an ossiculoplasty, revealed an overall median gain of 18.3 dB at 2 months, 22.3 dB at 6 months, and 25 dB 1 year postoperatively on Fletcher frequencies. An air-bone gap closure within 20 dB was achieved in 81% of all cases 1 year postoperatively. No cases of extrusion have been seen in our series. CONCLUSION: Our findings suggest that malleus allografts are capable of generating good and stable functional results as malleus-stapes assembly.