Fluctuations in Vestibular Afferent Excitability in Menière's Disease.

Objective: To determine if Menière's disease is associated with fluctuations in afferent excitability in four human subjects previously implanted with vestibular stimulators.

Study Design: Longitudinal repeated measures.

Setting: Tertiary referral center, human vestibular research laboratory.

Results From a Second-Generation Vestibular Implant in Human Subjects: Diagnosis May Impact Electrical Sensitivity of Vestibular Afferents.

Objective: Auditory and vestibular outcomes after placement of a vestibular-cochlear implant in subjects with varying causes of vestibular loss.

Study Design: Prospective case study.

Setting: Tertiary referral center.

Mandarin tone recognition in English speakers with normal hearing and with cochlear implants.

Mandarin-speaking cochlear implant users have difficulty perceiving tonal changes in speech with current signal processing strategies. The purpose of this study was to evaluate whether English-speaking cochlear implant and normal hearing listeners can be trained to recognise closed-set Mandarin tones. The validity of using native-English speakers to evaluate Mandarin tone perception in cochlear implants was tested.

Hybrid Music Perception Outcomes: Implications for Melody and Timbre Recognition in Cochlear Implant Recipients.

Objective: To examine whether or not electric-acoustic music perception outcomes, observed in a recent Hybrid L24 clinical trial, were related to the availability of low-frequency acoustic cues not present in the electric domain.

Study Design: Prospective, repeated-measures, within-subject design.

Setting: Academic research hospital.

The Dynamics of Prosthetically Elicited Vestibulo-Ocular Reflex Function Across Frequency and Context in the Rhesus Monkey.

Electrical vestibular neurostimulation may be a viable tool for modulating vestibular afferent input to restore vestibular function following injury or disease. To do this, such stimulators must provide afferent input that can be readily interpreted by the central nervous system to accurately represent head motion to drive reflexive behavior. Since vestibular afferents have different galvanic sensitivity, and different natural sensitivities to head rotational velocity and acceleration, and electrical stimulation produces aphysiological synchronous activation of multiple afferents, it is difficult to assign a priori an appropriate transformation between head velocity and acceleration and the properties of the electrical stimulus used to drive vestibular reflex function, i.

Effects of age and hearing mechanism on spectral resolution in normal hearing and cochlear-implanted listeners.

Spectral resolution limits speech perception with a cochlear implant (CI) in post-lingually deaf adults. However, the development of spectral resolution in pre-lingually deaf implanted children is not well understood. Acoustic spectral resolution was measured as a function of age (school-age versus adult) in CI and normal-hearing (NH) participants using spectral ripple discrimination (SRD).

Loss of Afferent Vestibular Input Produces Central Adaptation and Increased Gain of Vestibular Prosthetic Stimulation.

Implanted vestibular neurostimulators are effective in driving slow phase eye movements in monkeys and humans. Furthermore, increases in slow phase velocity and electrically evoked compound action potential (vECAP) amplitudes occur with increasing current amplitude of electrical stimulation. In intact monkeys, protracted intermittent stimulation continues to produce robust behavioral responses and preserved vECAPs.

Vestibular implantation and longitudinal electrical stimulation of the semicircular canal afferents in human subjects.

Animal experiments and limited data in humans suggest that electrical stimulation of the vestibular end organs could be used to treat loss of vestibular function. In this paper we demonstrate that canal-specific two-dimensionally (2D) measured eye velocities are elicited from intermittent brief 2 s biphasic pulse electrical stimulation in four human subjects implanted with a vestibular prosthesis. The 2D measured direction of the slow phase eye movements changed with the canal stimulated.

Longitudinal performance of an implantable vestibular prosthesis.

Loss of vestibular function may be treatable with an implantable vestibular prosthesis that stimulates semicircular canal afferents with biphasic pulse trains. Several studies have demonstrated short-term activation of the vestibulo-ocular reflex (VOR) with electrical stimulation. Fewer long-term studies have been restricted to small numbers of animals and stimulation designed to produce adaptive changes in the electrically elicited response.

Optimal combination of neural temporal envelope and fine structure cues to explain speech identification in background noise.

The dichotomy between acoustic temporal envelope (ENV) and fine structure (TFS) cues has stimulated numerous studies over the past decade to understand the relative role of acoustic ENV and TFS in human speech perception. Such acoustic temporal speech cues produce distinct neural discharge patterns at the level of the auditory nerve, yet little is known about the central neural mechanisms underlying the dichotomy in speech perception between neural ENV and TFS cues. We explored the question of how the peripheral auditory system encodes neural ENV and TFS cues in steady or fluctuating background noise, and how the central auditory system combines these forms of neural information for speech identification.

Prosthetic implantation of the human vestibular system.

Hypothesis: A functional vestibular prosthesis can be implanted in human such that electrical stimulation of each semicircular canal produces canal-specific eye movements while preserving vestibular and auditory function.

Background: A number of vestibular disorders could be treated with prosthetic stimulation of the vestibular end organs. We have previously demonstrated in rhesus monkeys that a vestibular neurostimulator, based on the Nucleus Freedom cochlear implant, can produce canal-specific electrically evoked eye movements while preserving auditory and vestibular function.

Postural responses to electrical stimulation of the vestibular end organs in human subjects.

A multichannel vestibular prosthesis that delivers electrical stimulation to the perilymph of individual semicircular canals is a potential new treatment modality for patients with vestibular deficiencies. Most research in this field has evaluated the efficacy of this approach by its ability to reproduce eye movements in response to head rotations. Our group has developed such a device and implanted it in four human subjects with intractable unilateral Meniere's disease.

Improved perception of music with a harmonic based algorithm for cochlear implants.

The lack of fine structure information in conventional cochlear implant (CI) encoding strategies presumably contributes to the generally poor music perception with CIs. To improve CI users' music perception, a harmonic-single-sideband-encoder (HSSE) strategy was developed , which explicitly tracks the harmonics of a single musical source and transforms them into modulators conveying both amplitude and temporal fine structure cues to electrodes. To investigate its effectiveness, vocoder simulations of HSSE and the conventional continuous-interleaved-sampling (CIS) strategy were implemented.

Longitudinal performance of a vestibular prosthesis as assessed by electrically evoked compound action potential recording.

Electrical stimulation of the vestibular end organ with a vestibular prosthesis may provide an effective treatment for vestibular loss if the stimulation remains effective over a significant period of time after implantation of the device. To assess efficacy of electrical stimulation in an animal model, we implanted 3 rhesus monkeys with a vestibular prosthesis based on a cochlear implant. We then recorded vestibular electrically evoked compound action potentials (vECAPs) longitudinally in each of the implanted canals to see how the amplitude of the response changed over time.

An experimental vestibular neural prosthesis: design and preliminary results with rhesus monkeys stimulated with modulated pulses.

A vestibular neural prosthesis was designed on the basis of a cochlear implant for treatment of Meniere's disease and other vestibular disorders. Computer control software was developed to generate patterned pulse stimuli for exploring optimal parameters to activate the vestibular nerve. Two rhesus monkeys were implanted with the prototype vestibular prosthesis and they were behaviorally evaluated post implantation surgery.

Maximizing the spectral and temporal benefits of two clinically used sound processing strategies for cochlear implants.

Previous work showed that the Fidelity120 processing strategy provides better spectral sensitivity, while the HiResolution processing strategy can deliver more detailed temporal information for Advanced Bionics cochlear implant users. The goal of this study was to develop a new sound processing strategy by maximizing the spectral benefit of Fidelity120 and the temporal benefit of HiResolution to improve both aspects of hearing. Using acoustic simulations of Fidelity120 and HiResolution strategies, a dual-processing strategy was created by combining Fidelity120 in the low frequency channels and HiResolution in the high frequency channels.

Improved perception of speech in noise and Mandarin tones with acoustic simulations of harmonic coding for cochlear implants.

Harmonic and temporal fine structure (TFS) information are important cues for speech perception in noise and music perception. However, due to the inherently coarse spectral and temporal resolution in electric hearing, the question of how to deliver harmonic and TFS information to cochlear implant (CI) users remains unresolved. A harmonic-single-sideband-encoder [(HSSE); Nie et al.

The ability of cochlear implant users to use temporal envelope cues recovered from speech frequency modulation.

Previous studies have demonstrated that normal-hearing listeners can understand speech using the recovered "temporal envelopes," i.e., amplitude modulation (AM) cues from frequency modulation (FM).

Implantation of the semicircular canals with preservation of hearing and rotational sensitivity: a vestibular neurostimulator suitable for clinical research.

Hypothesis: It is possible to implant a stimulating electrode array in the semicircular canals without damaging rotational sensitivity or hearing. The electrodes will evoke robust and precisely controlled eye movements.

Background: A number of groups are attempting to develop a neural prosthesis to ameliorate abnormal vestibular function.

Auditory outcomes following implantation and electrical stimulation of the semicircular canals.

We measured auditory brainstem responses (ABRs) in eight Rhesus monkeys after implantation of electrodes in the semicircular canals of one ear, using a multi-channel vestibular prosthesis based on cochlear implant technology. In five animals, click-evoked ABR thresholds in the implanted ear were within 10 dB of thresholds in the non-implanted control ear. Threshold differences in the remaining three animals varied from 18 to 69 dB, indicating mild to severe hearing losses.

Real-time communication of head velocity and acceleration for an externally mounted vestibular prosthesis.

Loss of vestibular function results in imbalance, disorientation, and oscillopsia. Several groups have designed and constructed implantable devices to restore vestibular function through electrical stimulation of the vestibular nerve. We have designed a two-part device in which the head motion sensing and signal processing elements are externally mounted to the head, and are coupled through an inductive link to a receiver stimulator that is based on a cochlear implant.

Acoustic temporal modulation detection and speech perception in cochlear implant listeners.

The goals of the present study were to measure acoustic temporal modulation transfer functions (TMTFs) in cochlear implant listeners and examine the relationship between modulation detection and speech recognition abilities. The effects of automatic gain control, presentation level and number of channels on modulation detection thresholds (MDTs) were examined using the listeners' clinical sound processor. The general form of the TMTF was low-pass, consistent with previous studies.

Relationship between behavioral and physiological spectral-ripple discrimination.

Previous studies have found a significant correlation between spectral-ripple discrimination and speech and music perception in cochlear implant (CI) users. This relationship could be of use to clinicians and scientists who are interested in using spectral-ripple stimuli in the assessment and habilitation of CI users. However, previous psychoacoustic tasks used to assess spectral discrimination are not suitable for all populations, and it would be beneficial to develop methods that could be used to test all age ranges, including pediatric implant users.

Characterization of the electrically evoked compound action potential of the vestibular nerve.

Objective: We recorded intraoperative and postoperative electrically evoked compound action potentials (ECAPs) in rhesus monkeys implanted with a vestibular neurostimulator. The objectives were to correlate the generation of slow-phase nystagmus or eye twitches induced by electrical stimulation of the implanted semicircular canal with the presence or absence of the vestibular ECAP responses and to assess the effectiveness of ECAP monitoring during surgery to guide surgical insertion of electrode arrays into the canals.

Design: Four rhesus monkeys (a total of 7 canals) were implanted with a vestibular neurostimulator modified from the Nucleus Freedom cochlear implant.