Andreas Büchner

Impact of Low-Frequency Hearing

Today, cochlear implantation is the treatment of choice in the case of severe to profound hearing loss, but the speech perception abilities of many recipients in noisy conditions are still poor and the overall sound quality and ease of listening still require improvement. Residual low-frequency hearing has been associated with improved hearing performance in cochlear implant patients, especially in difficult listening environments (i.e. cocktail party effect). It seems that low-frequency information can enhance the segregation of competing voices, which leads to better speech understanding in noise. We investigated the effect of low-frequency hearing on speech perception performance in a group of subjects being implanted with the Nucleus Hybrid-L device. The Hybrid-L device is a modified Nucleus Freedom implant, which instead of the standard electrode carries a very delicate electrode array that allows preservation of residual hearing to a great extent. Sentence test results from 22 subjects are presented here. Additionally, for 8 subjects, the acoustically presented frequency range was limited to 300, 500 and 700 Hz, and speech perception tests with a single competing talker were conducted. The Hybrid-L study group achieved a speech reception threshold of 15.9 dB in the hearing aid alone condition, 10.8 dB in the cochlear implant alone condition, and 3.9 dB when using the combination of cochlear implant and hearing aid. Differences between the 3 conditions are statistically significant. Results from the additional experiment on the acoustically presented frequency range suggest that very limited residual hearing below 500 Hz is already sufficient to produce a significant improvement in speech perception performance in conjunction with a cochlear implant.

Hearing Preservation Outcomes with Different Cochlear Implant Electrodes: Nucleus® Hybrid™-L24 and Nucleus Freedom™ CI422

Objectives: In recent years, it has been possible to preserve hearing after cochlear implantation in patients with significant amounts of low-frequency residual hearing. Due to the dimensions and characteristics of the cochlear implants (CIs) Nucleus® Hybrid™-L24 and Nucleus Freedom™ CI422, both can be used to preserve residual hearing. The aim was to investigate the degree and progression of hearing preservation over a longitudinal postoperative period in a large consecutive cohort of implanted patients with preoperative residual hearing who received either the Nucleus Hybrid-L24 or the Nucleus Freedom CI422 implant. The intention was to examine potential characteristics and triggers of resulting postoperative hearing loss which may support a differentiation of CI candidacy criteria for a certain implant type. Methods: A retrospective data analysis of patient files on consecutively implanted subjects presenting with a severe-to-profound sensorineural hearing loss at frequencies >1,500 Hz and substantial residual hearing at frequencies ≤1,500 Hz, implanted with a Nucleus Hybrid-L24 (n = 97) or a CI422 implant (n = 100), was undertaken. A single-subject repeated-measure design comparing the mean threshold shift for pure-tone thresholds under headphones up to 24 months after implantation was used. Results: Hearing preservation is observed in the majority of subjects with either implant (250-1,500 Hz frequency range). Hybrid-L24 patients exhibited a median hearing loss of 10 dB at initial fitting (n = 97) and of 15 dB after 24 months (n = 51). A 14.4-dB decrease in median hearing loss at initial fitting (n = 100) and a 30-dB decrease after 24 months (n = 28) was observed with the CI422 electrode. At initial fitting, 54.6% of the Hybrid-L24 (n = 97) and 49.0% of the CI422 (n = 100) subjects showed a mean threshold shift <15 dB. After 24 months, 58.8% (Hybrid-L24, n = 51) and 28.6% (CI422, n = 28) of the patients showed a mean threshold shift <15 dB. Conclusions: The results indicate that residual hearing was preserved for the majority of implanted patients with the Hybrid-L24 and the CI422 implant. Patients implanted with the Hybrid-L24 implant demonstrate greater stability and less median hearing loss over time than those with the CI422 implant. Assessments of onset and stability of hearing loss prior to implantation are important factors to consider during candidacy evaluation for electrode selection to potentially maximize the performance outcome for each patient.

Cochlear implant performance in geriatric patients

To evaluate the hearing performance with cochlear implants (CIs) in patients who were 70 years or older at the time of implantation (geriatric patients) and compare it with the performance in younger adults.

Speech comprehension in children and adolescents after sequential bilateral cochlear implantation with long interimplant interval.

Objective Identify likely predictors for the outcome after contralateral cochlear implantation with a long interimplant delay. Study Design Retrospective case reviews. Setting Outpatient cochlear implant (CI) center. Patients Seventy-three children and adolescents who underwent sequential bilateral cochlear implantation with an interval between both implantations of 5 years or longer. The mean age of the patients at the first and second cochlear implantations was 2.72 ± 1.52 and 11.57 ± 2.9 years, respectively. The mean duration of experience with both implants was 4.01 ± 1.57 years. Intervention Rehabilitative. Main Outcome Measures All 73 patients underwent periodic speech perception testing in quiet and noise. The most recent unilateral data for each side were statistically analyzed. The speech test results were evaluated by the age at first implantation, the interval between both implantations, the duration of hearing aid use in the second side, and the duration of the bilateral CI use. Results A statistically significant difference for speech test results was obtained between the early-implanted ears and the late-implanted ears for all children. These results were dependent on the interimplant interval. All age groups demonstrated significant differences (p > 0.05) for the second side between the speech test results and the interval between both cochlear implantations. In addition, statistically significant differences influenced by the duration of hearing aid use were found for speech test results for the second side. Experience was also a factor for the second CI, yielding significantly higher speech test scores with longer use. Conclusion The development of hearing abilities in a second-implanted side depends on the interimplant interval, the hearing aid use, and the duration of the second CI use.

The results in patients implanted with the nucleus double array cochlear implant: pitch discrimination and auditory performance.

Objective In patients with total or surgically inaccessible cochlear obliteration, only a reduced number of active electrodes can be inserted with standard cochlear implants, resulting in below average auditory performance. Therefore, a special implant with two electrode arrays was developed on the basis of the Nucleus 22 cochlear implant, the so-called Double Array. One electrode array with 11 active electrodes is inserted into the basal turn of the cochlea, while the second array with 10 active electrodes is inserted into the second turn. The Double Array is now available on the basis of the more advanced Nucleus 24 with 11 active electrodes on each array and two reference electrodes, one at the case and the second one an additional ball electrode, which is placed under the temporalis muscle. For device description and surgical technique see Lenarz et al. (2001). This paper presents psychophysical data on pitch discrimination and auditory performance of patients implanted with a Double Array on the basis of the Nucleus 22. Study Design A prospective intra-individual study using a Latin square paradigm was performed in six adult patients with obliterated cochlea who received the Nucleus 22 Double Array. After appropriate fitting and loudness balancing, patients were tested either with the basal, the apical or both electrode arrays. Apart from auditory performance tests including numbers and monosyllable word tests, pitch discrimination was determined with a defined procedure. Results When activating each array alone, auditory performance was better with the basal array than with the apical array. Both arrays together showed marked improvement compared with the basal array, indicating an additional effect of the second array. Pitch discrimination was significantly better for the electrodes in the basal turn than in the second turn, indicating differences in electrical excitation of the auditory nerve fibers. Pitch discrimination was positively correlated with auditory performance data. Conclusion The additional apical array leads to significant improvement in auditory performance in patients with obliterated cochleae by increasing the number of intracochlear electrodes. Despite reduced pitch discrimination, the apical array provides important information for speech recognition. For this reason the Double Array provides a profound advantage for patients with obliterated or surgically inaccessible cochleae.

Signal processing strategies for cochlear implants using current steering

In contemporary cochlear implant systems, the audio signal is decomposed into different frequency bands, each assigned to one electrode. Thus, pitch perception is limited by the number of physical electrodes implanted into the cochlea and by the wide bandwidth assigned to each electrode. The Harmony HiResolution bionic ear (Advanced Bionics LLC, Valencia, CA, USA) has the capability of creating virtual spectral channels through simultaneous delivery of current to pairs of adjacent electrodes. By steering the locus of stimulation to sites between the electrodes, additional pitch percepts can be generated. Two new sound processing strategies based on current steering have been designed, SpecRes and SineEx. In a chronic trial, speech intelligibility, pitch perception, and subjective appreciation of sound were compared between the two current steering strategies and standard HiRes strategy in 9 adult Harmony users. There was considerable variability in benefit, and the mean results show similar performance with all three strategies.

Temporal Feature Perception in Cochlear Implant Users

For the perception of timbre of a musical instrument, the attack time is known to hold crucial information. The first 50 to 150 ms of sound onset reflect the excitation mechanism, which generates the sound. Since auditory processing and music perception in particular are known to be hampered in cochlear implant (CI) users, we conducted an electroencephalography (EEG) study with an oddball paradigm to evaluate the processing of small differences in musical sound onset. The first 60 ms of a cornet sound were manipulated in order to examine whether these differences are detected by CI users and normal-hearing controls (NH controls), as revealed by auditory evoked potentials (AEPs). Our analysis focused on the N1 as an exogenous component known to reflect physical stimuli properties as well as on the P2 and the Mismatch Negativity (MMN). Our results revealed different N1 latencies as well as P2 amplitudes and latencies for the onset manipulations in both groups. An MMN could be elicited only in the NH control group. Together with additional findings that suggest an impact of musical training on CI users’ AEPs, our findings support the view that impaired timbre perception in CI users is at partly due to altered sound onset feature detection.

Long-Term Performance of Cochlear Implants in Postlingually Deafened Adults

Objective To evaluate the stability of long-term hearing performance after cochlear implantation (CI) in postlingually deafened adults and to explore the boundaries and limitations of the present test batteries for adult CI patients. Study Design Case series with chart review. Setting Tertiary referral center. Subjects and Methods A cohort of 1005 postlingually deafened adult cochlear implantees, who received their implants after age 18 years, was unilaterally implanted and had no inner ear malformations or cochlear ossification. Hearing performance with cochlear implant was evaluated with the help of 5 standard German speech tests. Results The average performance improved significantly during the first 6 months in all tests (learning phase) and afterward entered a plateau phase in which no statistically significant improvements or deteriorations were observed for more than 20 years of follow-up. For each test, the average performance of the cohort, the ceiling effect, and the average results for high and low performers are presented. Conclusions In this study, postlingually deafened adults required about 6 months to learn how to process the artificial signals delivered by the cochlear implant. After this learning phase, the hearing performance entered a stable plateau phase for more than 20 years. This stability reveals the long-term reliability of the technology and the biological stability of the electrode-nerve interface over years. In this study, the authors also evaluated the “ceiling effect” with 5 standard German speech tests, used for evaluation of postlingually deafened adult CI patients.

Comparison of dual-time-constant and fast-acting automatic gain control (AGC) systems in cochlear implants

Cochlear implants usually employ an automatic gain control (AGC) system as a first stage of processing. AGC1 was a fast-acting (syllabic) compressor. AGC2 was a dual-time-constant system; it usually performed as a slow-acting compressor, but incorporated an additional fast-acting system to provide protection from sudden increases in sound level. Six experienced cochlear-implant users were tested in a counterbalanced order, receiving one-month of experience with a given AGC type before switching to the other type. Performance was evaluated shortly after provision of a given AGC type and after one-month of experience with that AGC type. Questionnaires, mainly relating to listening in quiet situations, did not reveal significant differences between the two AGC types. However, fixed-level and roving-level tests of sentence identification in noise both revealed significantly better performance for AGC2. It is suggested that the poorer performance for AGC1 occurred because AGC1 introduced cross-modulation between the target speech and background noise, which made perceptual separation of the target and background more difficult.

Residual Neural Processing of Musical Sound Features in Adult Cochlear Implant Users

Auditory processing in general and music perception in particular are hampered in adult cochlear implant (CI) users. To examine the residual music perception skills and their underlying neural correlates in CI users implanted in adolescence or adulthood, we conducted an electrophysiological and behavioral study comparing adult CI users with normal-hearing age-matched controls (NH controls). We used a newly developed musical multi-feature paradigm, which makes it possible to test automatic auditory discrimination of six different types of sound feature changes inserted within a musical enriched setting lasting only 20 min. The presentation of stimuli did not require the participants’ attention, allowing the study of the early automatic stage of feature processing in the auditory cortex. For the CI users, we obtained mismatch negativity (MMN) brain responses to five feature changes but not to changes of rhythm, whereas we obtained MMNs for all the feature changes in the NH controls. Furthermore, the MMNs to deviants of pitch of CI users were reduced in amplitude and later than those of NH controls for changes of pitch and guitar timber. No other group differences in MMN parameters were found to changes in intensity and saxophone timber. Furthermore, the MMNs in CI users reflected the behavioral scores from a respective discrimination task and were correlated with patients’ age and speech intelligibility. Our results suggest that even though CI users are not performing at the same level as NH controls in neural discrimination of pitch-based features, they do possess potential neural abilities for music processing. However, CI users showed a disrupted ability to automatically discriminate rhythmic changes compared with controls. The current behavioral and MMN findings highlight the residual neural skills for music processing even in CI users who have been implanted in adolescence or adulthood. Highlights: - Automatic brain responses to musical feature changes reflect the limitations of central auditory processing in adult Cochlear Implant users.- The brains of adult CI users automatically process sound features changes even when inserted in a musical context.- CI users show disrupted automatic discriminatory abilities for rhythm in the brain.- Our fast paradigm demonstrate residual musical abilities in the brains of adult CI users giving hope for their future rehabilitation.