The University of Melbourne/Cochlear Corporation (Nucleus) Program

Familiar and unfamiliar speaker recognition assessment and system emulation for cochlear implant users

In the area of speech processing, human speaker identification under naturalistic environments is a challenging task, especially for hearing-impaired individuals with cochlear implants (CIs) or hearing aids (HAs). Motivated by the fact that electrodograms reflect direct CI stimulation of input audio, this study proposes a speaker identification (ID) investigation using two-dimensional electrodograms constructed from the responses of a CI auditory system to emulate CI speaker ID capabilities. Features are extracted from electrodograms through an identity vector (i-vector) framework to train and generate identity models for each speaker using a Gaussian mixture model-universal background model followed by probabilistic linear discriminant analysis. To validate the proposed system, perceptual speaker ID for 20 normal hearing (NH) and seven CI listeners was evaluated with a total of 41 different speakers and compared with the scores from the proposed system. A one-way analysis of variance showed that the proposed system can reliably predict the speaker ID capability of CI (F[1,10] = 0.18, p = 0.68) and NH (F[1,20] = 0, p = 0.98) listeners in naturalistic environments. The impact of speaker familiarity is also addressed, and the results show a reduced performance for speaker recognition by CI subjects using their CI processor, highlighting limitations of current speech processing strategies used in CIs/HAs.

[Organisation of a cochlear implant programme]

A cochlear implant (CI) programme brings together a number of professionals who, during the stages of selection, surgery, programming, rehabilitation and monitoring, develop a series of tasks aimed at promoting comprehensive attention to the implanted patient. The aim of this paper was to describe in detail the tasks in each of the phases described in a programme of CI, materials and necessary equipment and the role of the professionals involved. It also raised a number of recommendations on how to develop a CI programme gradually to facilitate the progression from the simplest to the most complex cases.

Evaluación del implante coclear como técnica de tratamiento de la hipoacusia profunda en pacientes pre y post locutivos

INTRODUCTION

These are the objectives planned for this study: 1. Evaluate the results from the communication point of view. 2. Evaluate the cochlear implant (CI) impact on the quality of life. 3. Evaluate medical complications and technical failures. 4. Assess direct and indirect costs generated during the phases of a cochlear implantation programme. 5. Determine which factors have a high impact on the clinical evolution and the financial cost.

MATERIALS AND METHOD

A population of 877 patients, postlingual and prelingual, adults and children, have been studied. They were treated in 5 Spanish centres with cochlear implant programmes. Audiometric tests and global questionnaires on life quality have been carried out. Medical and CI technology complications have also been computed. Direct and indirect economic costs of a cochlear implant have been calculated.

RESULTS

Postlocutive-implanted patients reached the 40 dB SPL threshold in the Pure Tone Audiometry, and this result was maintained during the 12-year evolution. In Vowels test, it evolved from a 30% on pre-stimulation to 80-90%, in Disyllables words test it evolved from a 10% to a 50-60%, and in CID Sentences test it evolved from an 18% to a 60-70%. In the prelocutive population, results were influenced by the child's age at implantation. The best results were obtained by the children who had been implanted earlier. Those implanted between 0 and 3 years old evolved in the Vowels test from 0% during pre-stimulation to 95%, from a 0% to a 90% in Disyllables words test and from a 0% to a 90-95% in CID Sentences test. Also, the speech acquisition and development of the pre-locutive population was also influenced by the implantation age. An 80% of postlocutive adult patients stated a mood and sociability improvement after the cochlear implantation. They did not show health changes in general nor relevant modifications in the attention they usually received from relatives and friends. Severe medical-surgical complications were registered for a 3.42% of the cases, a 7.06% of mild medical-surgical complications and a 3.07% of technical breakdowns in the internal components of the CI. Financial cost of implantation for a post-locutive adult oscillated between 36,912 Euro and 37,048 Euro, and between 37,689 Euro and 44,273 Euro for a pre-locutive child.

CONCLUSIONS

Cochlear implants clearly enhance communication skills of the implantees. Results obtained for the prelocutive implanted population justify the creation of hearing screening programmes in new-borns. Postlocutive implanted adults have expressed satisfaction for the results obtained. However, they did perceive some limitations in situations of unfavourable acoustic conditions. An analysis of direct and indirect costs related to a CI programme has been made. It may be useful to carry out reports on the cost-benefit ratio in this field. The low index of complications observed shows which cochlear implant treatment technique complies with the adequate safety margins. The factors influencing the most in the evolution are: duration of hearing deprivation, age at implantation, cochlear anatomy and functionality of the auditory pathway, patient's and relative's motivation, and the coexistence of other handicaps associated to hearing losses.

A Model for Cochlear Implant Electrode Insertion and Force Evaluation: Results with a New Electrode Design and Insertion Technique

OBJECTIVES AND HYPOTHESIS

This study has the specific aim of evaluating the insertion characteristics of a new cochlear implant electrode. Techniques for evaluation of fluoroscopic real time mechanical insertion dynamics, histologic electrode position and trauma results, hydraulic force, and mechanical insertion forces are presented. In addition, this study should serve to present a novel model for cochlear implant electrode insertion evaluations.

STUDY DESIGN

Prospective analysis using a series of analytical techniques.

METHODS

All studies are conducted in fixed cadaveric temporal bones. Real time fluoroscopic insertion evaluations, histologic evaluations for trauma and electrode position in embedded bones, hydraulic measures, and mechanical intracochlear force measurements are conducted with a current and new electrode.

RESULTS

The Contour Advance electrode provides a more reliable and less traumatic insertion when deployed with the Advance Off Stylet technique. This is largely because of a reduction in intracochlear outer wall force generation. Fluoroscopic and histologic analysis reveal a smooth insertion without reliance on cochlear outer wall contact. No hydraulic forces were detected when measured from the superior semicircular canal ampulla.

CONCLUSION

The model used for this study provides valuable information to cochlear implant surgeons and design engineers. The Contour Advance electrode, inserted with the Advance Off Stylet technique, represents an improvement over the Contour electrode inserted with the standard insertion technique.

The Mayo Clinic Experience with the Cochlear Implant

The implantati on of a cochlear electronic prosthetic device is an accept able means of improving the communication ability of pre- and postlinguaIIy deafened children and adults. A significant number of patients in this series are in the senior citizen age group. It has been beneficial in improving communication ability in selected profoundly deafened individuals. There has been a significant improvement in the cochlear electronic prosthetic device since the initial report of Djourno1 in 1957.

Comparison of half-band and full-band electrodes for intracochlear electrical stimulation

It was hypothesized that intracochlear stimulating electrodes oriented toward the modiolus would require a lower stimulus current to elicit a threshold neural response than longitudinal band electrodes. Electrically evoked auditory brain stem responses (EABRs) and electrode impedances were recorded with full-band and oriented half-band scala tympani electrodes in anesthetized, deafened cats. To elicit a threshold EABR, the stimulus current required for stimulation through half-band electrodes oriented toward the modiolus was not significantly different from the current required for stimulation through full-band electrodes. The impedances of full-band electrodes were significantly lower than those of half-band electrodes. Considering the significantly higher impedance and current density of half-band electrodes in comparison to full-band electrodes, as well as the critical orientation of half-band electrodes during implantation, we believe that full-band electrodes have advantages over half-band electrodes for scala tympani implantation.

Inexpensive cochlear implant device

We have developed a cochlear implant (CI) device modified from the House/3M cochlear implant device. The cost of raw materials was about $25. We used a new and simple technique for coating the implanted coil. We modified the circuit and removed the amplitude-modulated circuit. With this modification, the device uses less electricity and fewer transistors. There are slightly more than 3,000 patients using CI devices all over the world. Millions of profoundly deaf patients are poor and cannot afford the CI device that is now commercially available. Any university with well-trained otolaryngologists and physicists or electrical engineers can perform this technique.

Effects of level on nonspectral frequency difference limens for electrical and acoustic stimuli

The purpose of this experiment was to study the effects of stimulus level on discrimination of frequency as represented in the temporal waveforms of acoustic and electrical signals. The subjects were four nonhuman primates in which one ear had been deafened and implanted with an electrode array and the other ear was untreated. Frequency difference limens for 100 Hz electrical sinusoidal stimulation via a cochlear implant in the deafened ear were compared to those for 100 Hz sinusoidally amplitude-modulated white noise (SAM noise) acoustic stimuli to the normal-hearing contralateral ear. To correct for loudness cues, levels of the test stimuli were varied relative to the reference-stimulus level. The test-stimulus levels at which the percent responses were minimum were determined. These levels were used to measure the frequency difference limens. Frequency difference limens for the electrical stimuli decreased as a function of reference-stimulus level through most of the dynamic range, while those for the acoustic stimuli reached a minimum at 20 dB to 40 dB above threshold. For the electrical stimuli the slopes and relative positions of the frequency difference limen vs. level functions varied from subject to subject, and with changes in electrode configuration within a subject. These differences were related to threshold level and dynamic range. At higher levels of stimulation, frequency difference limens for acoustic and electrical stimuli fell in the same range. The slopes and relative positions of the frequency difference limen vs. level functions for electrical stimuli did not parallel those of level difference limen vs. level functions collected simultaneously from the same ears. The data suggest that nonspectral frequency discrimination may depend on the number of nerve fibers stimulated. With prostheses in cochleas with less than a full complement of auditory nerve fibers, the data suggest that stimulation level is an important variable influencing discriminability.

Temporal bone computed tomography in the preoperative evaluation for cochlear implantation

High resolution computed tomography of the temporal bone is performed routinely in the preoperative evaluation for cochlear implantation. A retrospective review was performed to determine the effect of these studies. The clinical significance was determined through consultation with the referring otolaryngologist and review of the operative reports. Twelve examinations were reviewed. Abnormalities were identified in 12 of the 24 ears examined (eight of 12 patients studied). In two patients the CT examination strongly influenced the selection of the ear to be implanted. In four additional cases information felt to be useful in preoperative planning was provided. Useful information related to potential complications with the mechanical insertion of the electrode apparatus. We conclude that temporal bone abnormalities are common in the population undergoing cochlear implantation and that high resolution temporal bone CT is essential in preoperative evaluation. The CT scan should be interpreted with adequate knowledge of the operative procedure to evaluate any possible barriers to the mechanical insertion of the internal components of the system.

Computer-generated three-dimensional reconstruction of the cochlea

Computer-generated three-dimensional reconstructions of the nerve fibers from the organ of Corti to the spiral ganglion were used to determine the optimum maximal length of the cochlear implant electrode. The spiral ganglion within the modiolus is much shorter than the organ of Corti. The spiral ganglion has 1 3/4 turns and reaches no higher than the middle of the second turn of the organ of Corti, which has 2 3/4 turns. The spiral ganglion is concentric and basal with respect to the organ of Corti. The spiral ganglion dendrites within the osseous spiral lamina of the basal turn project radially, nearly perpendicular to the central axis of the modiolus. Upon entering the modiolus, they turn basally at an angle of approximately 120 degrees. The projection of dendrites within the osseous spiral lamina became increasingly oblique as the ganglion extended apically. The organization of the cochlear nerve results from the spiraling of the ganglion. These findings are in agreement with previous reports. Implications of these findings and their possible relevance to the optimum length of the cochlear implant electrode are discussed with reference to cochlear damage resulting from longer electrodes.

Multichannel cochlear implants in partially ossified cochleas

Deposition of bone within the fluid spaces of the cochlea is encountered commonly in cochlear implant candidates and previously has been considered a relative contraindication to the use of multichannel intracochlear electrodes. This contraindication has been based on possible mechanical difficulty with electrode insertion as well as uncertainty about the potential benefit of the multichannel device in the patient. Fifteen profoundly deaf patients with partial ossification of the basal turn of the cochlea received implants with long intracochlear electrodes (11, Nucleus; 1, University of California at San Francisco/Storz; and 3, Symbion/Inneraid). In 11 cases, ossification had been predicted preoperatively by computed tomographic scan. Electrodes were completely inserted in 14 patients, and partial insertion was accomplished in one patient. All patients currently are using their devices and nine of 12 postlingually deaf patients have achieved some degree of open-set speech discrimination. This series demonstrates that in experienced hands, insertion of long multichannel electrodes into partially ossified cochleas is possible and that results are similar to those achieved in patients who have nonossified cochleas.

Use of multichannel cochlear implants in obstructed and obliterated cochleas

Obstruction that occurs within the scala tympani (after meningitis or otosclerosis) has been considered a contraindication for placement of a multichannel cochlear implant electrode. Two patients who exhibited radiographic evidence of intracochlear narrowing and obliteration were implanted with multichannel electrodes. Implantation involved creation of a channel for the electrode to wrap around the modiolus. The middle ear cavity and the external auditory canal also had to be removed to gain access. The response of one of the patients was similar to that of patients with normal cochlear anatomy who use multichannel devices. These early experiences, along with one case in which a single-channel electrode was placed, is presented.