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Introduction: When mapping cochlear implant (CI) patients with limited reporting abilities, the lowest electrical stimulus level that produces a stapedial reflex (i.e., the electrical stapedius reflex threshold [eSRT]) can be measured to estimate the upper bound of stimulation on individual or a subset of CI electrodes. However, eSRTs measured for individual electrodes or a subset of electrodes cannot be used to predict the global adjustment of electrical stimulation levels needed to achieve comfortable loudness sensations that can be readily used in a speech coding strategy. In the present study, eSRTs were measured for 1-, 4-, and 15-electrode stimulation to (1) determine changes in eSRT levels as a function of the electrode stimulation mode and (2) determine which stimulation mode eSRT levels best approximate comfortable loudness levels from patients' clinical maps., Methods: eSRTs were measured with the 3 different electrical stimulation configurations in 9 CI patients and compared with behaviorally measured, comfortable loudness levels or M-levels from patients' clinical maps., Results: A linear, mixed-effects, repeated-measures analysis revealed significant differences (p < 0.01) between eSRTs measured as a function of the stimulation mode. No significant differences (p = 0.059) were measured between 15-electrode eSRTs and M-levels from patients' clinical maps. The eSRTs measured for 1- and 4-electrode stimulation differed significantly (p < 0.05) from the M-levels on the corresponding electrodes from the patients' clinical map., Conclusion: eSRT profiles based on 1- or 4-electrode stimulation can be used to determine comfortable loudness level on either individual or a subset of electrodes, and 15-electrode eSRT profiles can be used to determine the upper bound of electrical stimulation that can be used in a speech coding strategy., (© 2021 S. Karger AG, Basel.)

Objective: Determine if changes in middle ear absorbance measured with wide-band tympanometry (WBT) occur following hearing-preservation cochlear implantation (CI). Such measures may provide insight into the mechanisms of acoustic hearing loss postimplantation., Study Design: Clinical capsule report., Setting: Tertiary academic referral center., Design: WBT absorbance was measured bilaterally during pre- and postoperative clinical office visits in five unilaterally-implanted cochlear implant recipients. Pre- and postoperative WBT measures were compared within each subject in the implanted and contralateral, unimplanted ears., Results: In general, WBT absorbance measurements show a broad spectral pattern including two or three distinct peaks measured over a frequency range of 226 to 8000 Hz. Grand average and linear mixed model comparisons between the pre- and postoperative WBT patterns show significantly reduced (p < 0.05) low-frequency absorbance in the implanted ears in the frequency region over 0.6 to 1.1 kHz, but not in the unimplanted ears. The maximum effect occurred at 1 kHz with absorbance decreasing from ∼0.8 to ∼0.5 after implantation. The limited data are consistent with expected relationships between WBT absorbance and air- and bone-conduction thresholds, assuming an increased air-bone gap reflects conductive hearing loss., Conclusion: Cochlear implantation can result in reduction of low-frequency acoustic absorbance as measured by WBT. WBT may be a useful and sensitive tool for monitoring the mechanical status of the middle and inner ears following cochlear implantation.

Objectives: The upper loudness limit of electrical stimulation in cochlear implant patients is sometimes set using electrically elicited stapedius reflex thresholds (eSRTs), especially in children for whom reporting skills may be limited. In unilateral cochlear implant patients, eSRT levels are measured typically in the contralateral unimplanted ear because the ability to measure eSRTs in the implanted ear is likely to be limited due to the cochlear implant surgery and consequential changes in middle ear dynamics. This practice is particularly limiting in the case of fitting bilaterally implanted pediatric cases because there is no unimplanted ear option to choose for eSRT measurement. The goal of this study was to identify an improved measurement protocol to increase the success of eSRT measurement in ipsilateral or contralateral or both implanted ears of pediatric cochlear implant recipients. This work hypothesizes that use of a higher probe frequency (e.g., 1000 Hz compared with the 226 Hz standard), which is closer to the mechanical middle ear resonant frequency, may be more effective in measuring middle ear muscle contraction in either ear., Design: In the present study, eSRTs were measured using multiple probe frequencies (226, 678, and 1000 Hz) in the ipsilateral and contralateral ears of 19 children with unilateral Advanced Bionics (AB) cochlear implants (mean age = 8.6 years, SD = 2.29). An integrated middle ear analyzer designed by AB was used to elicit and detect stapedius reflexes and assign eSRT levels. In the integrated middle ear analyzer system, an Interacoustics Titan middle ear analyzer was used to perform middle ear measurements in synchrony with research software running on an AB Neptune speech processor, which controlled the delivery of electrical pulse trains at varying levels to the test subject. Changes in middle ear acoustic admittance following an electrical pulse train stimulus indicated the occurrence of an electrically elicited stapedius reflex., Results: Of the 19 ears tested, ipsilateral eSRTs were successfully measured in 3 (16%), 4 (21%), and 7 (37%) ears using probe tones of 226, 678, and 1000 Hz, respectively. Contralateral eSRT levels were measured in 11 (58%), 13 (68%), and 13 (68%) ears using the three different probe frequencies, respectively. A significant difference was found in the incidence of successful eSRT measurement as a function of probe frequency in the ipsilateral ears with the greatest pair-wise difference between the 226 and 1000 Hz probe. A significant increase in contralateral eSRT measurement success as a function of probe frequency was not found. These findings are consistent with the idea that changes in middle ear mechanics, secondary to cochlear implant surgery, may interfere with the detection of stapedius muscle contraction in the ipsilateral middle ear. The best logistic, mixed-effects model of the occurrence of successful eSRT measures included ear of measurement and probe frequency as significant fixed effects. No significant differences in average eSRT levels were observed across ipsilateral and contralateral measurements or as a function of probe frequency., Conclusion: Typically, measurement of stapedius reflexes is less successful in the implanted ears of cochlear implant recipients compared with measurements in the contralateral, unimplanted ear. The ability to measure eSRT levels ipsilaterally can be improved by using a higher probe frequency.

Objectives: Monopolar stimulation of the most apical electrode produces the lowest pitch sensation in cochlear implants clinically. A phantom electrode that uses out-of-phase electrical stimulation between the most apical and the neighboring basal electrode can produce a lower pitch sensation than that associated with the most apical electrode. However, because of the absence of contacts beyond the apical tip of the array, the ability to assess the spread of electrical excitation associated with phantom stimulation is limited in the typical cochlear implant subject with no residual hearing. In the present study, the spread of electrical excitation associated with monopolar and phantom stimulation of the most apical electrode was assessed using electrical masking of acoustic thresholds in cochlear implant subjects with residual, low-frequency, acoustic hearing., Design: Eight subjects with an Advanced Bionics cochlear implant and residual hearing in the implanted ear participated in this study (nine ears in total). Unmasked and masked thresholds for acoustic pure tones were measured at 125, 250, 500, 750, 1000, and 2000 Hz in the presence of monopolar and phantom electrode stimulation presented at the apical-most end of the array. The current compensation for phantom electrode stimulation was fixed at 50%. The two electrical maskers were loudness balanced. Differences between the unmasked and masked acoustic thresholds can be attributed to (1) the electrical stimulus-induced interference in the transduction/conduction of the acoustic signal through cochlear periphery and the auditory nerve and/or (2) masking at the level of the central auditory system., Results: The results show a significant elevation in pure-tone thresholds in the presence of the monopolar and phantom electrical maskers. The unmasked thresholds were subtracted from the masked thresholds to derive masking patterns as a function of the acoustic probe frequency. The masking patterns show that phantom stimulation was able to produce more masking than that associated with the monopolar stimulation of the most apical electrode., Conclusion: These results suggest that for some cochlear implant subjects, phantom electrode stimulation can shift the neural stimulation pattern more apically in the cochlea, which is consistent with reports that phantom electrode stimulation produces lower pitch sensations than those associated with monopolar stimulation of the most apical electrode alone.

Objective: A great deal of variability exists in the speech-recognition abilities of postlingually deaf adult cochlear implant (CI) recipients. A number of previous studies have shown that duration of deafness is a primary factor affecting CI outcomes; however, there is little agreement regarding other factors that may affect performance. The objective of the present study was to determine the source of variability in CI outcomes by examining three main factors, biographic/audiologic information, electrode position within the cochlea, and cognitive abilities in a group of newly implanted CI recipients., Design: Participants were 114 postlingually deaf adults with either the Cochlear or Advanced Bionics CI systems. Biographic/audiologic information, aided sentence-recognition scores, a high resolution temporal bone CT scan and cognitive measures were obtained before implantation. Monosyllabic word recognition scores were obtained during numerous test intervals from 2 weeks to 2 years after initial activation of the CI. Electrode position within the cochlea was determined by three-dimensional reconstruction of pre- and postimplant CT scans. Participants' word scores over 2 years were fit with a logistic curve to predict word score as a function of time and to highlight 4-word recognition metrics (CNC initial score, CNC final score, rise time to 90% of CNC final score, and CNC difference score)., Results: Participants were divided into six outcome groups based on the percentile ranking of their CNC final score, that is, participants in the bottom 10% were in group 1; those in the top 10% were in group 6. Across outcome groups, significant relationships from low to high performance were identified. Biographic/audiologic factors of age at implantation, duration of hearing loss, duration of hearing aid use, and duration of severe-to-profound hearing loss were significantly and inversely related to performance as were frequency modulated tone, sound-field threshold levels obtained with the CI. That is, the higher-performing outcome groups were younger in age at the time of implantation, had shorter duration of severe-to-profound hearing loss, and had lower CI sound-field threshold levels. Significant inverse relationships across outcome groups were also observed for electrode position, specifically the percentage of electrodes in scala vestibuli as opposed to scala tympani and depth of insertion of the electrode array. In addition, positioning of electrode arrays closer to the modiolar wall was positively correlated with outcome. Cognitive ability was significantly and positively related to outcome; however, age at implantation and cognition were highly correlated. After controlling for age, cognition was no longer a factor affecting outcomes., Conclusion: There are a number of factors that limit CI outcomes. They can act singularly or collectively to restrict an individual's performance and to varying degrees. The highest performing CI recipients are those with the least number of limiting factors. Knowledge of when and how these factors affect performance can favorably influence counseling, device fitting, and rehabilitation for individual patients and can contribute to improved device design and application.

Objectives/hypothesis: An intraoperative monitoring algorithm during cochlear implant electrode insertion could be used to detect trauma and guide electrode placement relative to surviving hair cells. The aim of this report was to assess the feasibility of using extracochlear recording sites to monitor acoustically evoked responses from surviving hair cells and neural elements during implantation in an animal model., Study Design: Animal experiments., Methods: The normal-hearing gerbil was used. Two recording methods, one using a lock-in amplifier and another using Fourier analysis of recorded signals, were used to obtain frequency-specific information about the responses to tones. Amplitude and threshold determinations were made at the round window and at three extracochlear sites. To induce intracochlear damage, a platinum-iridium wire was inserted through the round window. The wire was advanced, and changes in the potentials were correlated with cochlear contact. Anatomic integrity was assessed using cochlea whole mount preparations., Results: In general, the lock-in amplifier showed greater sensitivity and lower thresholds at higher frequencies relative to the Fourier method. Also, the lock-in amplifier was more resistant to masking effects. Both systems were able to detect loss of cochlear potentials secondary to intracochlear trauma. Histologic damage was seen in all cases and corresponded to electrophysiologic changes., Conclusions: Impact of electrodes on cochlear structures affecting cochlear performance could be detected from several extracochlear sites. The lock-in amplifier demonstrated greater sensitivity and resistance to noise when compared to the fast Fourier transform recording paradigm. The latter showed greater flexibility of detecting and separating hair cell and neural potentials., (Copyright © 2011 The American Laryngological, Rhinological, and Otological Society, Inc.)

Objectives/hypothesis: To introduce a novel method of combining robotics and the CO(2) laser micromanipulator to provide excellent precision and performance repeatability designed for surgical applications., Study Design: Pilot feasibility study., Methods: We developed a portable robotic controller that appends to a standard CO(2) laser micromanipulator. The robotic accuracy and laser beam path repeatability were compared to six experienced users of the industry standard micromanipulator performing the same simulated surgical tasks. Helium-neon laser beam video tracking techniques were employed., Results: The robotic controller demonstrated superiority over experienced human manual micromanipulator control in accuracy (laser path within 1 mm of idealized centerline), 97.42% (standard deviation [SD] 2.65%), versus 85.11% (SD 14.51%), P = .018; and laser beam path repeatability (area of laser path divergence on successive trials), 21.42 mm(2) (SD 4.35 mm(2) ) versus 65.84 mm(2) (SD 11.93 mm(2) ), P = .006., Conclusions: Robotic micromanipulator control enhances accuracy and repeatability for specific laser tasks. Computerized control opens opportunity for alternative user interfaces and additional safety features., (Copyright © 2011 The American Laryngological, Rhinological, and Otological Society, Inc.)

Objective: This study aimed to provide guidelines to optimize perception of soft speech and speech in noise for Advanced Bionics cochlear implant (CI) users., Design: Three programs differing in T-levels were created for ten subjects. Using the T-level setting that provided the lowest FM-tone, sound-field threshold levels for each subject, three additional programs were created with input dynamic range (IDR) settings of 50, 65 and 80 dB., Study Sample: Subjects were postlinguistically deaf adults implanted with either the Clarion CII or 90K CI devices., Results: Sound-field threshold levels were lowest with T-levels set higher than 10% of M-levels and with the two widest IDRs. Group data revealed significantly higher scores for CNC words presented at a soft level with an IDR of 80 dB and 65 dB compared to 50 dB. Although no significant group differences were seen between the three IDRs for sentences in noise, significant individual differences were present., Conclusions: Setting Ts higher than the manufacturer's recommendation of 10% of M-levels and providing IDR options can improve overall speech perception; however, for some users, higher Ts and wider IDRs may not be appropriate. Based on the results of the study, clinical programming recommendations are provided.

While 3-dimensional (3D) imaging by computed tomography has long been desirable for research and treatment of cochlear-implant patients, technical challenges have limited its wide application. Recent developments in scanner hardware and image processing techniques now allow image quality improvements that make clinical applications feasible. Validation experiments were performed to characterize a new methodology and its imaging performance.

Objectives: A new technique for determining the position of each electrode in the cochlea is described and applied to spiral computed tomography data from 15 patients implanted with Advanced Bionics HiFocus I, Ij, or Helix arrays., Methods: ANALYZE imaging software was used to register 3-dimensional image volumes from patients' preoperative and postoperative scans and from a single body donor whose unimplanted ears were scanned clinically, with micro computed tomography and with orthogonal-plane fluorescence optical sectioning (OPFOS) microscopy. By use of this registration, we compared the atlas of OPFOS images of soft tissue within the body donor's cochlea with the bone and fluid/ tissue boundary available in patient scan data to choose the midmodiolar axis position and judge the electrode position in the scala tympani or scala vestibuli, including the distance to the medial and lateral scalar walls. The angular rotation 0 degrees start point is a line joining the midmodiolar axis and the middle of the cochlear canal entry from the vestibule., Results: The group mean array insertion depth was 477 degrees (range, 286 degrees to 655 degrees). The word scores were negatively correlated (r = -0.59; p = .028) with the number of electrodes in the scala vestibuli., Conclusions: Although the individual variability in all measures was large, repeated patterns of suboptimal electrode placement were observed across subjects, underscoring the applicability of this technique.

Objective: To compare two methods of minimizing cochlear implant artifact in cortical auditory evoked potential (CAEP) recordings., Methods: Two experiments were conducted. In the first, we assessed the use of independent component analysis (ICA) as a pre-processing filter. In the second, we explored the use of an optimized differential reference (ODR) for minimizing artifacts., Results: Both ICA and the ODR can minimize the artifact and allow measurement of CAEP responses., Conclusions: When using a large number of recording electrodes ICA can be used to minimize the implant artifact. When using a single electrode montage an optimized differential reference is adequate to minimize the artifact., Significance: The use of an optimized differential reference could allow cortical evoked potentials to be used in routine clinical assessment of auditory pathway development in children and adults fit with cochlear implants.

To understand the auditory neural response to electrical stimuli similar to those used in a cochlear implant, it will be necessary to understand the neural refraction and summation response kinetics. Evidence exists indicating that the cell soma may alter the auditory neural response kinetics and could be the site of conduction failure for excitation initiated on the peripheral process. There is, however, reason to believe that the excitation site in some healthy, type I neurons and in pathological, type III neurons is the central process of the cell. To characterize the neural response to activation at a controlled central process site, cat auditory neurons were stimulated with an intrameatal electrode, and the summation and refraction response kinetics were measured. This approach was used to: (1) characterize the behavior of the neural response to central process excitation; (2) make comparisons between intrameatal excitation at a known central site and scala tympani excitation at an unknown site; and (3) provide membrane characterization free from the possible alteration of membrane kinetics produced by the cell soma. The membrane kinetics measured using intrameatal stimulation differ from those recorded with scala tympani stimulation indicating that the mechanisms for scala tympani and intrameatal stimulation differ.

We describe a novel signal processing strategy for cochlear implants designed to emphasize stochastic independence across the excited neural population. The strategy is based on the observation that high rate pulse trains may produce random spike patterns in auditory nerve fibers that are statistically similar to those produced by spontaneous activity in the normal cochlea. We call this activity 'pseudospontaneous'. A supercomputer-based computational model of a population of auditory nerve fibers suggests that different average rates of pseudospontaneous activity can be created by varying the stimulus current of a fixed-amplitude, high-rate pulse train, e.g. 5000 pps. Electrically-evoked compound action potentials recorded in a human cochlear implant subject are consistent with the hypothesis that such a stimulus can desynchronize the fiber population. This desynchronization may enhance neural representation of temporal detail and dynamic range with a cochlear implant and eliminate a major difference between acoustic and electric hearing.

Objective: This study aimed to assess, in one profoundly hearing impaired subject, potential benefits and limitations in placing bilaterally implanted scala tympani electrode arrays under control of a single speech processor., Study Design: All available stimulation sites in both ears were compared in studies of pitch discrimination and pitch ranking, identifying three bilateral pairs capable of supporting interaural comparisons with no perceptible difference in pitch. Using those pairs, the subject's ability to lateralize sound was studied as a function of interaural time delay and interaural amplitude difference. Consonant identification scores were obtained for continuous interleaved sampling processors using various unilateral and bilateral combinations of electrodes., Results: For loudness-matched stimuli composed of 50-msec bursts of 80-microsec/phase pulses at 480 pulses/sec, the subject was able to identify the ear receiving the earlier onset for interaural delays at least as brief as 150 microsec for all three matched pairs. For similar simultaneous stimuli, the subject could identify the ear receiving the louder signal for the smallest deviations from loudness-matched amplitudes available from the implanted electronics. The consonant studies found no evidence that bilateral stimulation per se degrades speech processor performance, even for arbitrary divisions of information between the two ears. Additional contralateral as well as ipsilateral channels were observed to improve speech processor performance., Conclusions: The ability of this subject to lateralize sounds on the basis of interaural delay or loudness difference, combined with the consonant identification results, supports further use of coordinated binaural stimulation to improve cochlear implant users' ability to understand speech, especially in the presence of competing speech noise.

Multielectrode cochlear prostheses seek to approximate the cochlea's normal frequency-place mapping through spatial segregation of stimulus currents. Various electrode configurations have been employed to achieve such segregation. Direct measurements of stimulation regions among single auditory nerve (AN) fibers has been possible only when normal hearing is preserved, such that each fiber's cochlear place can be inferred from its tuning curve. This precludes measurements in deafened ears, or ears compromised by implantation of the electrodes. Data presented here demonstrate that the cochlear place of an AN fiber can be estimated without acoustic sensitivity, using electrical microstimulation through a recording pipette in the AN bundle. The procedure exploits cochleotopic projection to isofrequency laminae within the contralateral inferior colliculus (IC). Microstimulation excites a small group of fibers neighboring the recorded fiber, generating centrally propagated volleys along a narrow frequency-specific pathway. Evoked potential recordings at varying depths are made to identify the ICC lamina where the response to AN microstimulation is greatest. Preliminary data are also presented for an alternative method of identifying the lamina using a frequency domain measure of binaural interactions within the IC.

Objective: To record and characterize intracochlear evoked potentials (EPs) for a variety of electrical stimuli in studies with cochlear implant patients., Methods: Recordings were made with patients having direct percutaneous access to their implanted electrodes. Intracochlear voltages were recorded via unstimulated electrodes. The stimuli included trains of identical pulses, with pulse rates ranging from 100 to 4065/s, and a modulated pulse train produced by a single-channel speech processor, with the pulse rate of 824/s., Results: Magnitudes of EPs for each pulse in trains of identical pulses were uniform for pulse rates below about 200/s. For rates between about 400 and 1000/s, an alternating pattern of EP magnitudes was observed, with relatively large EPs following the odd-numbered pulses. For rates between about 1000 and 3000/s, more complex patterns were observed. After the first millisecond of each train at even higher rates, uniform EPs again were observed across pulses, although the absolute magnitude of the EPs was much lower than that observed for low rates of stimulation. The approximate rates corresponding to boundaries between these different regions varied among subjects and among electrodes within subjects. EP magnitudes for the modulated pulse train reflected the gross periodicity of the modulation waveform but did not reflect temporal details within the periods., Conclusions: Population responses of the human auditory nerve, as indicated by EP magnitudes, reflect the amplitudes of electrical pulses for pulse rates below about 200/s and above about 3000/s. Use of intermediate rates may introduce distortions in the transmission of stimulus information with cochlear implants.

The interface between electrode and neural target tissue is thought to influence certain characteristics of neural and behavioral responses to electrical stimulation of the auditory system. At present, the biophysical properties of this interface are not well understood. Here the effects of biphasic phase duration and electrode configuration on psychophysical threshold in response to electrical stimulation in cats are described. Five cats were trained to respond to acoustic stimuli using food as a reward in an operant reinforcement paradigm. After training, the animals were unilaterally deafened and implanted with a multicontact intracochlear electrode array. Thresholds for single presentations of biphasic current pulses were measured as a function of phase duration and electrode arrangement. Statistical analyses of the data indicated that strength-duration function slopes between 200 and 1600 microseconds/phase were significantly different for the different electrode configurations and, overall, were unrelated to the absolute level of the strength-duration function (i.e., were independent of absolute threshold). For all subjects, the slope of this function for intermediate pulse durations was dependent on electrode configuration and most shallow for radial-bipolar configurations (-3.4 dB/doubling), was steepest for monopolar arrangements (-5.9 dB/doubling), and was intermediate for longitudinal-bipolar pairings. (-4.4 dB/doubling). Slopes for both shorter and longer phase duration stimuli were not significantly different. The underlying mechanisms for these effects may include, or be a combination of altered electrical field patterns, integrated activity across multiple fibers, and stochastic behavior of individual auditory neurons to electrical stimulation.

Examples from several areas of cochlear implant research are presented, with emphasis on the continuous interleaved sampling (CIS) approach to speech processor design. Within-subject comparisons of such processors with the compressed analog (CA) approach of the clinical Ineraid device are reviewed, and ongoing similar comparisons with the clinical Nucleus spectral peak (SPEAK) strategy are outlined. Correlations between chronic performance levels with clinical CA processors and initial performance levels with CIS, data on further improvements in performance with chronic use of CIS, and instances of substantial benefit from custom fitting of CIS parameters are presented as examples of findings with immediate clinical implications. New studies are described, involving the measurement of intracochlear evoked potentials in response to cochlear implant stimulation, and the integration of such work with computer modeling studies.

New strategies for representing acoustic information with multichannel cochlear implants have produced substantial improvements in speech recognition for implant users. This report reviews within-subject comparison of a new continuous interleaved sampling (CIS) strategy with a compressed analog (CA) strategy used in a standard clinical device. In general, the comparison show higher levels of open-set speech recognition with CIS for each of the 11 subjects studied. Data on the importance of the patients variable in determining outcomes with cochlear implants are presented. A brief description of another new strategy, the spectral maxima sound processor (SMSP) strategy is given as well as information on the availability of CIS in various implant systems.

Estimates of electrical auditory brainstem response (EABR) thresholds are compared with behavioral thresholds for electrical stimulation in the same subject using identical stimuli and electrode configurations. Four cats were behaviorally trained to measure acoustic auditory thresholds using food as a reward in an operant reinforcement paradigm. One of the animals was then implanted, in an otherwise normal ear, with a scaled-UCSF multi-contact electrode array containing four intracochlear electrodes. Three animals were implanted with an electrode array containing eight intracochlear contacts and one extracochlear contact under the temporalis muscle following unilateral cochlear perfusion with 10% neomycin solution. Stimuli for the behavioral studies were single presentations of 200 us/phase biphasic current pulses. For the EABR studies, the same stimulus was presented at a rate of 32/s. In general, for the animal with the four-contact array and two of the three subjects with the eight-contact implant, changes in electrode configuration produced well-differentiated changes in threshold. For these three subjects, comparisons of behavioral and EABR thresholds for the majority of monopolar and bipolar electrode configurations tested showed excellent agreement (r2 = 0.88). Correlations between behavioral and EABR measures in these animals were comparable for bipolar and monopolar arrangements (r2 = 0.88 for bipolar and 0.87 for monopolar). For one subject with the eight-contact electrode, who showed similar monopolar and bipolar electrode behavioral thresholds for all tested electrode spacings or configurations, most EABR thresholds were substantially higher than, and poorly correlated with, behavioral thresholds (r2 = 0.15; r2 = 0.28 for monopolar arrangements, and r2 = 0.12 for bipolar arrangements).

Within-subjects comparisons of processing strategies for cochlear implants are reviewed. Compressed analog strategies were compared to interleaved pulses strategies in tests with one group of 8 subjects, and to continuous interleaved sampling strategies in tests with another group of 11 subjects. The tests included open-set recognition of words and sentences. The results show that, while different strategies may produce quite different outcomes across subjects, individual performances with one processing strategy are significantly correlated with those of alternative strategies. These findings emphasize the importance of patient variables in determining outcomes across a variety of prosthesis designs.

Two approaches for representing speech information with multichannel cochlear prostheses are being compared in tests with implant patients. Included in these studies are the compressed analog (CA) approach of a standard clinical device and research processors utilizing continuous interleaved sampling (CIS). Initial studies have been completed with nine subjects, seven of whom were selected on the basis of excellent performance with the Ineraid clinical processor, and the remaining two for their relatively poor performance with the same device. The tests include open-set recognition of words and sentences. Every subject has obtained a higher score--or repeated a score of 100% correct--on every test when using a CIS processor. These results are discussed in terms of their implications for processor design.

Various strategies for representing speech information with multichannel cochlear prostheses were compared in tests with implant patients. The strategies included the compressed analog (CA) approach of a standard clinical device, and alternative interleaved pulses (IP) and continuous interleaved sampling (CIS) strategies. CA and IP strategies had been compared in previous studies with a wide range of subjects. The present studies compared all three types in tests with one subject and CA and CIS strategies in tests with six additional subjects. Subjects for the present studies were selected for their excellent performance with the clinical CA processor, and the tests included closed-set identification of consonants and open-set recognition of words and sentences. For every test, every subject obtained his or her highest score, or repeated a score of 100% correct, using a CIS strategy. In the comparisons of all three approaches, IP processor scores were between those obtained with CA and CIS processors. The results are discussed in terms of their implications for processor design.

HIGH levels of speech recognition have been achieved with a new sound processing strategy for multielectrode cochlear implants. A cochlear implant system consists of one or more implanted electrodes for direct electrical activation of the auditory nerve, an external speech processor that transforms a microphone input into stimuli for each electrode, and a transcutaneous (rf-link) or percutaneous (direct) connection between the processor and the electrodes. We report here the comparison of the new strategy and a standard clinical processor. The standard compressed analogue (CA) processor presented analogue waveforms simultaneously to all electrodes, whereas the new continuous interleaved sampling (CIS) strategy presented brief pulses to each electrode in a nonoverlapping sequence. Seven experienced implant users, selected for their excellent performance with the CA processor, participated as subjects. The new strategy produced large improvements in the scores of speech reception tests for all subjects. These results have important implications for the treatment of deafness and for minimal representations of speech at the auditory periphery.

Comparisons of analog and pulsatile coding strategies for multichannel cochlear prostheses are reviewed. The results are related to design considerations for pediatric implants, including efficacy, safety, ease of fitting, and access to future improvements.

A wide variety of speech processing strategies for multichannel auditory prostheses were compared in studies of two patients implanted with the UCSF electrode array. Each strategy was evaluated using tests of vowel and consonant confusions, with and without lipreading. Included among the strategies were the compressed analog processor of the present UCSF/Storz prosthesis and a group of interleaved pulses processors in which the amplitudes of nonsimultaneous pulses code the spectral variations of speech. For these patients, each with indications of poor nerve survival, test scores were significantly higher with the interleaved pulses processors. We believe this superior performance was a result of 1. the substantial release from channel interactions provided by nonsimultaneous stimuli and 2. a fast enough rotation among the channels to support adequate temporal and spectral resolution of perceived speech sounds.

Rats with complete spinal transections were compressed in helium-oxygen to 120 bars. Tremors and increased EMG activity in limbs rostral as well as caudal to the lesions were observed beginning at 30 bars. Spinal seizures occurred at 95 bars, similar to cortical seizure thresholds of intact rats. Denervated limbs remained flaccid throughout the dives. No rostro-caudal progression of symptoms was evident in normal animals, but fluctuation of symptoms with increasing pressure was frequently observed. These findings are consistent with the hypothesis that the effects of pressure on aggregates of neurons exceed those on isolated components.