James F. Patrick

The development of the Nucleus Freedom Cochlear implant system.

Cochlear Limited (Cochlear™) released the fourth-generation cochlear implant system, Nucleus® Freedom™, in 2005. Freedom is based on 25 years of experience in cochlear implant research and development and incorporates advances in medicine, implantable materials, electronic technology, and sound coding. This article presents the development of Cochlears implant systems, with an overview of the first 3 generations, and details of the Freedom system: the CI24RE receiver-stimulator, the Contour Advance™ electrode, the modular Freedom processor, the available speech coding strategies, the input processing options of SmartSound™ to improve the signal before coding as electrical signals, and the programming software. Preliminary results from multicenter studies with the Freedom system are reported, demonstrating better levels of performance compared with the previous systems. The final section presents the most recent implant reliability data, with the early findings at 18 months showing improved reliability of the Freedom implant compared with the earlier Nucleus 3 System. Also reported are some of the findings of Cochlears collaborative research programs to improve recipient outcomes. Included are studies showing the benefits from bilateral implants, electroacoustic stimulation using an ipsilateral and/or contralateral hearing aid, advanced speech coding, and streamlined speech processor programming.

Speech processing method and apparatus

Signal processing system for converting a speech signal into a data signal for controlling a hearing prosthesis having an implanted electrode array adapted to stimulate the auditory nerve fibers of a patient by the application of electrical currents to selected electrodes in the array. The system generates an input signal current corresponding to a received speech signal. The amplitude and frequency of the fundamental voicing component of the speech signal is approximated as are the amplitude and frequency of at least one formant of the speech signal. A programmable microprocessor produces instructions which cause the application of electrical currents to selected groups of electrodes in the array with or without delays between the stimulation of each electrode in the groups. The microprocessor is programmable with data defining a predetermined relationship between each group of electrodes and a selected range of at least one formant frequency and with data defining a predetermined relationship between another formant frequency and the delay between stimulation of each electrode in each said group based on psychophysical testing of the patient. Selection of electrodes based on the estimated frequency of the formants produces the desired percepts in the auditory-like sensations generated in the patient. The microprocessor is further programmable to produce data which determines the level of stimulation of each selected group of electrodes and determines the delay between stimulation of electrodes in each group dependent on the estimated amplitude of formants of the speech signal as well as on predetermined data relating to the sensitivity of each electrode implanted in the patient.

Cochlear implant soft failures consensus development conference statement

COCHLEAR IMPLANT SOFT FAILURES CONSENSUS DEVELOPMENT CONFERENCE STATEMENTThis Consensus Statement was prepared by a panel of experts representing the fields of otolaryngology, audiology, speech and language pathology, communication science, and engineering. Representatives to the conference were app

Electrical stimulation of the midbrain for hearing restoration: Insight into the functional organization of the human central auditory system

The cochlear implant can restore speech perception in patients with sensorineural hearing loss. However, it is ineffective for those without an implantable cochlea or a functional auditory nerve. These patients can be implanted with the auditory brainstem implant (ABI), which stimulates the surface of the cochlear nucleus. Unfortunately, the ABI has achieved limited success in its main patient group [i.e., those with neurofibromatosis type 2 (NF2)] and requires a difficult surgical procedure. These limitations have motivated us to develop a new hearing prosthesis that stimulates the midbrain with a penetrating electrode array. We recently implanted three patients with the auditory midbrain implant (AMI), and it has proven to be safe with minimal movement over time. The AMI provides loudness, pitch, temporal, and directional cues, features that have shown to be important for speech perception and more complex sound processing. Thus far, all three patients obtain enhancements in lip reading capabilities and environmental awareness and some improvements in speech perception comparable with that of NF2 ABI patients. Considering that our midbrain target is more surgically exposable than the cochlear nucleus, this argues for the use of the AMI as an alternative to the ABI. Fortunately, we were able to stimulate different midbrain regions in our patients and investigate the functional organization of the human central auditory system. These findings provide some insight into how we may need to stimulate the midbrain to improve hearing performance with the AMI.

The Nucleus 22-channel cochlear implant system

Cochlear implants have become the treatment of choice for profoundly deaf adults and children who obtain little or no benefit from conventional amplification. Sounds are translated into small electric currents that stimulate the auditory nerves in the cochlea and generate hearing sensations. The Nucleus cochlear implant is the result of more than 20 yr of research and development, first at the University of Melbourne, Australia and later by Cochlear Proprietary Limited (Sydney, Australia) in collaboration with the University of Melbourne. Today, the cochlear Mini-22 implant system is approved by the United States Food and Drug Administration (FDA) for use in adults and children, and has been implanted in more than 3000 patients worldwide. Although this chapter describes the cochlear implant system and clinical issues related to its use in children, much of the material has been derived from experience with adults. Furthermore, the Nucleus system is not static. It is being continually improved both in performance and ease of use. The purpose of this chapter is to describe developments leading up to and including the present Nucleus cochlear implant system. Other chapters in this issue present results and procedures relating to pediatric applications of the device.

Current distributions in cochlear stimulation.

Animal experimental studies have shown length constants of 2-4 mm for bipolar and 8-16 mm for monopolar stimulations. Studies in models using saline-solution-filled tubes have allowed us to examine the radial and longitudinal current distribution for pseudobipolar stimulation and have demonstrated that current localization is the same for bipolar and pseudobipolar stimulation over a 6-10-dB operating range. With coincident pseudobipolar multiple-channel stimulation there was suppression of the current between the stimulus maxima and enhancement at the edges leading to less stimulus interaction. Experiments performed with a pseudobipolar electrode implanted into the human cochlea showed that there was significant spread of current along the ground electrode because the electrode ground impedance was significantly greater than the cochlear tissue impedances. Because this leads to less current returned at each ground electrode, the pseudobipolar array will result in less interaction for coincident stimulation.

Current Distribution Measurements Within the Human Cochlea

The magnitudes of the currents returned through each ground electrode fine of a multiple-electrode cochlear implant array were determined during surgical implantations on two patients. These were often found to be distributed widely to points far from the stimulus electrode site. Further measurements made in in vitro solutions demonstrated that the distributions were due largely to the ground electrode interface impedances being significantly larger than the fluid-path impedances, and demonstrated that distributions could be changed by modification of the ground electrode interface impedances.

Effects of phase duration and pulse rate on loudness and pitch percepts in the first auditory midbrain implant patients: Comparison to cochlear implant and auditory brainstem implant results

The auditory midbrain implant (AMI), which is designed for stimulation of the inferior colliculus (IC), is now in clinical trials. The AMI consists of a single shank array (20 contacts) and uses a stimulation strategy originally designed for cochlear implants since it is already approved for human use and we do not yet know how to optimally activate the auditory midbrain. The goal of this study was to investigate the effects of different pulse rates and phase durations on loudness and pitch percepts because these parameters are required to implement the AMI stimulation strategy. Although each patient was implanted into a different region (i.e. lateral lemniscus, central nucleus of IC, dorsal cortex of IC), they generally exhibited similar threshold versus phase duration, threshold versus pulse rate, and pitch versus pulse rate curves. In particular, stimulation with 100 mus/phase, 250 pulse per second (pps) pulse trains achieved an optimal balance among safety, energy, and current threshold requirements while avoiding rate pitch effects. However, we observed large differences across patients in loudness adaptation to continuous pulse stimulation over long time scales. One patient (implanted in dorsal cortex of IC) even experienced complete loudness decay and elevation of thresholds with daily stimulation. Comparing these results with those of cochlear implant and auditory brainstem implant patients, it appears that stimulation of higher order neurons exhibits less and even no loudness summation for higher rate stimuli and greater current leakage for longer phase durations than that of cochlear neurons. The fact that all midbrain regions we stimulated, which includes three distinctly different nuclei, exhibited similar loudness summation effects (i.e. none for pulse rates above 250 pps) suggests a possible shift in some coding properties that is affected more by which stage along the auditory pathway rather than the types of neurons are being stimulated. However, loudness adaptation occurs at multiple stages from the cochlea up to the midbrain.

A cochlear implant round window electrode array

This multiple-electrode array for round window cochlear implantation is a robust, reliable system for inserting 20 mm along the scala tympani with a minimum of trauma and can provide for bipolar stimulation.

Design and fabrication of the banded electrode array.

The banded electrode array is a simple and effective array for multiple-channel cochlear stimulation and meets the necessary design requirements.