Consensus panel on a cochlear coordinate system applicable in histologic, physiologic, and radiologic studies of the human cochlea.

Hypothesis: An objective cochlear framework, for evaluation of the cochlear anatomy and description of the position of an implanted cochlear implant electrode, would allow the direct comparison of measures performed within the various subdisciplines involved in cochlear implant research.

Background: Research on the human cochlear anatomy in relation to tonotopy and cochlear implantation is conducted by specialists from numerous disciplines such as histologists, surgeons, physicists, engineers, audiologists, and radiologists. To allow accurate comparisons between and combinations of previous and forthcoming scientific and clinical studies, cochlear structures and electrode positions must be specified in a consistent manner.

Practical model description of peripheral neural excitation in cochlear implant recipients: 4. model development at low pulse rates: general model and application to individuals.

This fourth paper in the series presents the initial development of the model at low pulse rates, where refractory behavior is minimal. This is a necessary developmental stage that makes possible the subsequent incorporation of temporal effects, in the fifth paper. The model comprises a population of neural fibers spread along the cochlear duct, with normally distributed thresholds.

Practical model description of peripheral neural excitation in cochlear implant recipients: 5. refractory recovery and facilitation.

In this paper the neural response to electrical stimulation with short inter-pulse intervals was examined. The refractory recovery of the electrically-evoked compound action potential (ECAP) was recorded using masker pulses with a wide range of currents relative to the probe pulse. The ECAP was recorded in subjects implanted with the Nucleus 24 cochlear implant system (three with straight and two with Contour electrode arrays), using the Neural Response Telemetry (NRT) system.

Practical model description of peripheral neural excitation in cochlear implant recipients: 3. ECAP during bursts and loudness as function of burst duration.

In this, the third paper of the series, the loudness of low-rate bursts of electrical pulses was measured as a function of the burst duration, in subjects implanted with the Nucleus 24 cochlear implant system (three with straight and two with Contour electrode arrays). In order to help distinguish between the contributions of peripheral and more central effects, the ECAP was recorded to the individual pulses comprising the bursts, using the Neural Response Telemetry (NRT) system. At a pulse rate of 250 pulses/s, the ECAP amplitude did not decrease greatly during the bursts: the mean reduction factor was 0.

Practical model description of peripheral neural excitation in cochlear implant recipients: 1. Growth of loudness and ECAP amplitude with current.

This is the first in a series of five papers, presenting the development of a practical mathematical model that describes excitation of the auditory nerve by electrical stimulation from a cochlear implant. Here are presented methods and basic data for the subjects, who were implanted with the Nucleus 24 cochlear implant system (three with straight and three with Contour electrode arrays), required as background for all papers. The growth of subjective loudness with stimulus current was studied, for low-rate pulse bursts and for single pulses.

Practical model description of peripheral neural excitation in cochlear implant recipients: 2. Spread of the effective stimulation field (ESF), from ECAP and FEA.

This second paper of the series considers the spread of the "effective stimulation field" (ESF) produced by monopolar biphasic stimulation of an electrode within scala tympani, in subjects implanted with the Nucleus 24 cochlear implant system (three with straight and two with Contour electrode arrays). A novel measure of the ECAP was employed, using the Neural Response Telemetry (NRT) system. The ESF provides a patient-specific measure of the "ability" of the stimulation field to excite neurons at differing locations around the cochlea.

Psychophysical measures in patients fitted with Contour and straight Nucleus electrode arrays.

The objective of this study was to compare the psychophysical performance of patients using the Nucleus Contour electrode array with that of patients using the straight banded-electrode array. In particular, we wished to consider how psychophysical parameters would differ for an electrode array positioned closer to the modiolus, and how this might influence both patient benefits and the design of speech processing strategies. Nine subjects participated in the study: four used the Nucleus straight array and five used the Nucleus Contour electrode array.

A psychophysical forward masking comparison of longitudinal spread of neural excitation in the Contour and straight Nucleus electrode arrays.

The objective of the study was to compare the widths of forward masking profiles in subjects implanted with the Nucleus 24 Contour or straight electrode array. The Contour array is typically positioned closer to the modiolus than the straight array. Subjects were fourteen postlingually hearing-impaired adults with severe-profound hearing loss, seven used the Contour array and seven used the straight array.

Measurement and analysis of access resistance and polarization impedance in cochlear implant recipients.

Background: Impedance measurements are commonly performed at the end of cochlear implant surgery, not only to confirm that all electrodes are working but also to monitor the impedances of the newly implanted electrodes. The current method of testing allows the determination of only the overall electrode impedance but not its components, access resistance and polarization impedance. To determine whether any longitudinal change in the electrode impedance is caused by a change in the endocochlear environment or rather caused by a change in the surface quality of the electrode, it is necessary to extract access resistance and polarization impedance.

Spatial spread of neural excitation: comparison of compound action potential and forward-masking data in cochlear implant recipients.

The feasibility of using the electrically evoked compound action potential (ECAP), measured with the NRT system (Neural Response Telemetry) and the NRT software (version 2.04), to quantify the longitudinal spread of neural excitation was examined in four subjects fitted with the Nucleus C124M cochlear implant. The ECAP and psychophysical forward-masking profiles were measured using stimulation on each of three electrodes, in basal, middle and apical positions.

Degree of modiolar coiling, electrical thresholds, and speech perception after cochlear implantation.

Objective: Perimodiolar electrode arrays were developed to improve stimulation of specific neural populations and to decrease power consumption. Postoperative radiographs suggest that some arrays are more tightly coiled than others. The purpose of this study was to evaluate whether the degree of modiolar coil correlates with electrical threshold and/or performance measures postimplantation with the Nucleus CI24RCS (Contour) device.

Spatial spread of neural excitation in cochlear implant recipients: comparison of improved ECAP method and psychophysical forward masking.

This study introduces and evaluates a method for measurement of the longitudinal spread of electrically evoked neural excitation in the cochlea, using the Neural Response Telemetry system (NRT) available with the Nucleus((R)) 24 cochlear implant system. The recently released version of the NRT software (version 3.0) enables presentation of the 'masker' and 'probe' on different electrodes.