Speech perception performance as a function of stimulus pulse rate and processing strategy preference for the Cochlear Nucleus CI24RE device: relation to perceptual threshold and loudness comfort profiles.

Current cochlear implants can operate at high pulse rates. The effect of increasing pulse rate on speech performance is not yet clear. Habituation to low rates may affect the outcome. This paper presents the results of three subsequent studies using different experimental paradigms, applying the Nucleus CI24RE device, and conducted by ten European implant teams. Pulse rate per channel varied from 500 to 3500 pulses per second with ACE and from 1200 to 3500 pps with CIS strategy. The results showed that the first rate presented had little effect on the finally preferred rate. Lower rates were preferred. The effect of pulse rate on word scores of post-linguistic implantees was small; high rates tended to give lower scores. However, there were no significant differences between the word scores across subjects if collected at the individually preferred pulse rate. High pulse rates were preferred when the post-implantation threshold was low.

Residual hearing conservation and electroacoustic stimulation with the nucleus 24 contour advance cochlear implant.

OBJECTIVE: To assess the conservation of residual hearing in recipients of the Nucleus 24 Contour Advance cochlear implant (CI) and the benefits of combined electrical and acoustic stimulation. STUDY DESIGN: Prospective multicenter study. SETTING: CI clinics in Western Europe. PATIENTS: Adult candidates for conventional cochlear implantation with a minimum preoperative word recognition score of 10% in the ear to be implanted. INTERVENTION: "Soft-surgery" protocol, including a 1- to 1.2-mm anterior and inferior cochleostomy hole with the electrode array, inserted 17 mm using the "advance-off-stylet" technique. Patients with postoperative pure-tone hearing threshold levels (HTLs) of 80 dB hearing loss or less at 125 and 250 Hz and 90 dB hearing loss or less at 500 Hz were refitted with an in-the-ear hearing aid for combined ipsilateral electrical and acoustic (El-Ac) stimulation. MAIN OUTCOME MEASURES: A questionnaire to collect information regarding surgery. Pure-tone HTLs measured at intervals. Word recognition tested in quiet and sentence recognition tested in noise at 10 and 5 dB signal-to-noise ratio (SNR). HEARING CONSERVATION RESULTS: HTL data were available for 27 patients. HTLs were conserved within 20 dB of preoperative levels for 33, 26, and 19% of patients for 125, 250, and 500 Hz, respectively. However, the recommended soft-surgery protocol was strictly followed in only 12 of 27 patients. For these 12 patients, hearing thresholds were conserved within 20 dB for 50, 50, and 33% of patients. Median threshold increases were 40 dB (range, 250-500 Hz) for the whole group and 23 dB for the strict surgery group. Ten patients retained sufficient HTLs to enter the El-Ac user group. SPEECH RECOGNITION RESULTS: Group mean recognition scores for nine El-Ac users for words presented at 65 dB sound pressure level were 45% for CI alone and 55% for CI + ipsilateral hearing aid (p < 0.05, paired t). For sentences presented in noise at 5 dB SNR, mean word scores were 46% CI alone and 56% CI + ipsilateral hearing aid (p < 0.01, paired t). CONCLUSION: Hearing was conserved for conventional candidates for cochlear implantation where the recommended soft-surgery protocol was strictly adhered. Combined ipsilateral electrical and acoustic stimulation provided considerable benefits for speech recognition in noise, equivalent to between 3 and 5 dB SNR, compared with CI alone.

Preservation of residual hearing with cochlear implantation: how and why.

CONCLUSIONS: Hearing may be conserved in adults after implantation with the Nucleus Contour Advance perimodiolar electrode array. The degree of hearing preservation and the maximum insertion depth of the electrode array can vary considerably despite a defined surgical protocol. Residual hearing combined with electrical stimulation in the same ear can provide additional benefits even for conventional candidates for cochlear implantation. OBJECTIVES: We present preliminary results from a prospective multicentre study investigating the conservation of residual hearing after implantation with a standard-length Nucleus Contour Advance perimodiolar electrode array and the benefits of combined electrical and acoustic stimulation. MATERIAL AND METHODS: The subjects were 12 adult candidates for cochlear implantation recruited according to national selection criteria. A "soft" surgery protocol was defined, as follows: 1-1.2-mm cochleostomy hole anterior and inferior to the round window; Nucleus Contour Advance electrode array inserted using the "Advance-off-stylet" technique; and insertion depth controlled by means of three square marker ribs left outside the cochleostomy hole. These procedures had been shown to reduce insertion forces in temporal bone preparations. Variations in surgical techniques were monitored using a questionnaire. Pure-tone thresholds were measured pre- and postoperatively. Patients who still retained thresholds <90 dB HL for frequencies up to 500 Hz were re-fitted with an in-the-ear (ITE) hearing aid. Word recognition was tested in quiet and sentence perception in noise for the cochlear implant alone and in combination with an ipsilateral hearing aid. RESULTS: Hearing threshold level data were available for 12 patients recruited from 6 of the centres. Median increases in hearing threshold levels were 23, 27 and 33 dB for the frequencies 125, 250 and 500 Hz, respectively. These median increases include the data for two patients who had total loss of residual hearing due to difficulties encountered during surgery. "Cochlear view" X-ray images indicated that the depth of insertion varied between 300 and 430 degrees, despite modest variations in the length of the electrode inserted (17-19 mm). The insertion angle had some influence on the preservation of residual hearing at frequencies of 250-500 Hz. Six of the 12 patients retained sufficient hearing for effective use of an ipsilateral ITE hearing aid (< or = 80 dB HL at 125 and 250 Hz; < or = 90 dB HL at 500 Hz). Word recognition scores in quiet were improved from 10% to 30% with the cochlear implant plus ipsilateral hearing aid in 3 patients who had at least 3 months postoperative experience. Signal:noise ratio thresholds for sentence recognition were improved by up to 3 dB. Patients reported that they experienced greatly improved sound quality and preferred to use the two devices together.

Measurement of the electrically evoked compound action potential via a neural response telemetry system.

The main aim of this study was to validate a new technique, neural response telemetry (NRT), for measuring the electrically evoked compound action potential in adult cochlear implant users via their Nucleus C124M implant. Thirty-eight adults were evaluated with a variety of measurement procedures with the NRT software. Electrically evoked compound action potentials were obtained in 31 of the 38 adults (81.6%) and in 132 of the 160 electrodes (82.5%) tested. In addition to validating this technique, we also established a set of default clinical test parameters.

Evaluation of Neural Response Telemetry (NRT™) with focus on long-term rate adaptation over a wide range of stimulation rates.

Custom Sound EP™ (CSEP) is an advanced flexible software tool dedicated to recording of electrically evoked compound action potentials (ECAPs) in Nucleus® recipients using Neural Response Telemetry™ (NRT™). European multi-centre studies of the Freedom™ cochlear implant system confirmed that CSEP offers tools to effectively record ECAP thresholds, amplitude growth functions, recovery functions, spread of excitation functions, and rate adaptation functions and an automated algorithm (AutoNRT™) to measure threshold profiles. This paper reports on rate adaptation measurements. Rate adaptation of ECAP amplitudes can successfully be measured up to rates of 495 pulses per second (pps) by repeating conventional ECAP measurements and over a wide range of rates up to 8000 pps using the masked response extraction technique. Rate adaptation did not show a predictable relationship with speech perception and coding strategy channel rate preference. The masked response extraction method offers opportunities to study long-term rate adaptation with well-defined and controlled stimulation paradigms.

Results from a European clinical investigation of the Nucleus multichannel auditory brainstem implant.

OBJECTIVE: This study was designed to investigate the perceptual benefits and potential risks of implanting the Nucleus(R) multichannel auditory brainstem implant. DESIGN: Between September 1992 and October 1997 a total of 27 subjects received a Nucleus 20- or 21-channel Auditory Brainstem Implant (ABI). All subjects involved in the trial had bilateral acoustic tumour as a result of neurofibromatosis type 2 (NF2) resulting in complete dysfunction of the VIIIth nerve. The study used each subject as their own control without a preoperative baseline because residual hearing, if existing, was destroyed at surgery by tumour removal. A battery of speech tests was conducted to evaluate each patient's performance and communication abilities. Tests were conducted, where possible, in the auditory-only, visual-only, and auditory-visual conditions at 3 days postoperatively (baseline), at 3-mo intervals for the first year and every 12 mo thereafter. A subjective performance questionnaire was administered together with an extensive neurological examination at each test interval. RESULTS: 27 subjects involved in this trial were successfully implanted with a Nucleus ABI. One subject died 2 days postoperatively due to a lung embolism unrelated to the device. Twenty-six subjects underwent device activation and all but one patient received auditory sensation at initial stimulation (96.2%). On average 8.6 (+/-4.2) of the available 21 electrodes were used in the patients' MAPs. Performance evaluation measures showed that the majority of users had access to auditory information such as environmental sound awareness together with stress and rhythm cues in speech that assist with lipreading. Although most subjects did not achieve any functional auditory-alone, open-set speech understanding, two subjects from this series (7.4%) did receive sufficient benefit to be able to use the ABI in conversation without lipreading. CONCLUSIONS: Although the medical risks and surgical complexity associated with ABI device implantation are far greater than those for a cochlear implant, the clinical results from this trial show that the Nucleus multichannel ABI is capable of providing a significant patient benefit over risk ratio for subjects suffering loss of hearing due to bilateral retrocochlear lesions.