Elaboration of an instrument to evaluate the recognition of Brazilian melodies in children / Criação de um instrumento para avaliar o reconhecimento de melodias brasileiras em crianças

Abstract Introduction: There is evidence pointing to the importance of the evaluation of musical perception through objective and subjective instruments. In Brazil, there is a shortage of instruments that evaluates musical perception. Objective: To develop an instrument to evaluate the recognition of traditional Brazilian melodies and investigate the performance of children with typical hearing. Methods: The study was carried out after approval of the research ethics committee (1.198.607). The instrument was developed in software format with website access, using the languages PHP 5.5.12, Javascript, Cascade style sheets and "HTML5"; database "MYSQL 5.6.17" on the "Apache 2.4.9" server. Fifteen melodies of Brazilian folk songs were recorded in piano synthesized timbre, with 12 seconds per melody reproduction and four second intervals between them. A total of 155 schooled children, aged eight to 11 years, of both sexes, with typical hearing participated in the study. The test was performed in a silent room with sound stimuli amplified by a sound box at 65 dBNA, positioned at 0 azimuth, and at one meter from the participant, the notebook was used for children to play with on the screen on the title and illustration of the melody they recognized they were listening to. The responses were recorded on their own database. Results: The instrument titled "Evaluation of recognition of traditional melodies in children" can be run on various devices (computers, notebooks, tablets, mobile phones) and operating systems (Windows, Macintosh, Android, Linux). Access: http://192.185.216.17/ivan/home/login.php by login and password. The most easily recognized melody was "Cai, cai balão" (89%) and the least recognized was "Capelinha de melão" (25.2%). The average time to perform the test was 3′15″. Conclusion: The development and application of the software proved effective for the studied population. This instrument may contribute to the improvement of protocols for the evaluation of musical perception in children with hearing aid and/or cochlear implants users.

Resumo Introdução: Há evidências que apontam para a importância da avaliação da percepção musical através de instrumentos objetivos e subjetivos. No Brasil, há escassez de instrumentos que avaliem a percepção musical. Objetivo: Desenvolver um instrumento para avaliar o reconhecimento de melodias tradicionais brasileiras e investigar o desempenho de crianças com audição típica. Método: O estudo foi desenvolvido após aprovação do comitê de ética em pesquisa (1.198.607). O instrumento foi desenvolvido em formato de software com acesso ao site, com as linguagens de programação PHP 5.5.12, Javascript, Cascade Style Sheets e HTML5; banco de dados MYSQL 5.6.17 no servidor Apache 2.4.9. Quinze melodias de canções folclóricas brasileiras foram gravadas com timbre sintetizado em piano, com 12 segundos de reprodução da melodia e quatro segundos de intervalo entre elas. Participaram do estudo 155 crianças, alfabetizadas, entre oito e 11 anos, de ambos os sexos, com audição típica. O teste foi feito em sala silenciosa com estímulo sonoro amplificado por uma caixa sonora a 65 dB NA, posicionada a 0 azimute e a um metro do participante e o notebook foi usado para que as crianças brincassem na tela com o título e a ilustração da melodia que eles reconheceram que ouviam. As respostas foram registradas em seu próprio banco de dados. Resultados: O instrumento intitulado "Avaliação do reconhecimento de melodias tradicionais em crianças" pode ser executado em vários dispositivos (computadores, notebooks, tablets, telefones celulares) e sistemas operacionais (Windows, Macintosh, Android, Linux). Acesse: http://192.185.216.17/ivan/home/login.php através de login e senha. A melodia mais facilmente reconhecida foi "Cai cai balão" (89%) e a menos reconhecida foi "Capelinha de melão" (25,2%). O tempo médio para fazer o teste foi de 3′15″. Conclusão: O desenvolvimento e a aplicação do software se mostraram eficazes para a população estudada. Esse instrumento pode contribuir para o aprimoramento de protocolos de avaliação da percepção musical em crianças usuárias de próteses auditivas e/ou usuárias de implante coclear.

Don't look at it as a miracle cure: Contested notions of success and failure in family narratives of pediatric cochlear implantation.

Cochlear implants (CIs) are a routine treatment for children identified with a qualifying hearing loss. The CI, however, must be accompanied by a long-term and intense auditory training regimen in order to possibly acquire spoken language with the device. This research investigates families' experiences when they opted for the CI and undertook the task of auditory training, but the child failed to achieve what might be clinically considered "success" - the ability to function solely using spoken language. Using a science and technology studies informed approach that places the CI within a complex sociotechnical system, this research shows the uncertain trajectory of the CI, as well as the contingency of the very notions of success and failure. To do so, data from in-depth interviews with a diverse sample of parents (n = 11) were collected. Results show the shifting definitions of failure and success within families, as well as suggest areas for further exploration regarding clinical practice and pediatric CIs. First, professionals' messaging often conveyed to parents a belief in the infallibility of the CI, this potentially caused "soft failure" to go undetected and unmitigated. Second, speech assessments used in clinical measurements of outcomes did not capture a holistic understanding of a child's identity and social integration, leaving out an important component for consideration of what a 'good outcome' is. Third, minority parents experience structural racism and clinical attitudes that may render "failure" more likely to be identified and expected in these children, an individualizing process that allows structural failures to go uncritiqued.

Elaboration of an instrument to evaluate the recognition of Brazilian melodies in children.

INTRODUCTION: There is evidence pointing to the importance of the evaluation of musical perception through objective and subjective instruments. In Brazil, there is a shortage of instruments that evaluates musical perception. OBJECTIVE: To develop an instrument to evaluate the recognition of traditional Brazilian melodies and investigate the performance of children with typical hearing. METHODS: The study was carried out after approval of the research ethics committee (1.198.607). The instrument was developed in software format with website access, using the languages PHP 5.5.12, Javascript, Cascade style sheets and "HTML5"; database "MYSQL 5.6.17" on the "Apache 2.4.9" server. Fifteen melodies of Brazilian folk songs were recorded in piano synthesized timbre, with 12 seconds per melody reproduction and four second intervals between them. A total of 155 schooled children, aged eight to 11 years, of both sexes, with typical hearing participated in the study. The test was performed in a silent room with sound stimuli amplified by a sound box at 65dBNA, positioned at 0 azimuth, and at one meter from the participant, the notebook was used for children to play with on the screen on the title and illustration of the melody they recognized they were listening to. The responses were recorded on their own database. RESULTS: The instrument titled "Evaluation of recognition of traditional melodies in children" can be run on various devices (computers, notebooks, tablets, mobile phones) and operating systems (Windows, Macintosh, Android, Linux). Access: http://192.185.216.17/ivan/home/login.php by login and password. The most easily recognized melody was "Cai, cai balão" (89%) and the least recognized was "Capelinha de melão" (25.2%). The average time to perform the test was 3'15″. CONCLUSION: The development and application of the software proved effective for the studied population. This instrument may contribute to the improvement of protocols for the evaluation of musical perception in children with hearing aid and/or cochlear implants users.

Independent component analysis for cochlear implant artifacts attenuation from electrically evoked auditory steady-state response measurements.

OBJECTIVE: Electrically evoked auditory steady-state responses (EASSRs) are potentially useful for objective cochlear implant (CI) fitting and follow-up of the auditory maturation in infants and children with a CI. EASSRs are recorded in the electro-encephalogram (EEG) in response to electrical stimulation with continuous pulse trains, and are distorted by significant CI artifacts related to this electrical stimulation. The aim of this study is to evaluate a CI artifacts attenuation method based on independent component analysis (ICA) for three EASSR datasets. APPROACH: ICA has often been used to remove CI artifacts from the EEG to record transient auditory responses, such as cortical evoked auditory potentials. Independent components (ICs) corresponding to CI artifacts are then often manually identified. In this study, an ICA based CI artifacts attenuation method was developed and evaluated for EASSR measurements with varying CI artifacts and EASSR characteristics. Artifactual ICs were automatically identified based on their spectrum. MAIN RESULTS: For 40 Hz amplitude modulation (AM) stimulation at comfort level, in high SNR recordings, ICA succeeded in removing CI artifacts from all recording channels, without distorting the EASSR. For lower SNR recordings, with 40 Hz AM stimulation at lower levels, or 90 Hz AM stimulation, ICA either distorted the EASSR or could not remove all CI artifacts in most subjects, except for two of the seven subjects tested with low level 40 Hz AM stimulation. Noise levels were reduced after ICA was applied, and up to 29 ICs were rejected, suggesting poor ICA separation quality. SIGNIFICANCE: We hypothesize that ICA is capable of separating CI artifacts and EASSR in case the contralateral hemisphere is EASSR dominated. For small EASSRs or large CI artifact amplitudes, ICA separation quality is insufficient to ensure complete CI artifacts attenuation without EASSR distortion.

Auditory steady state responses and cochlear implants: Modeling the artifact-response mixture in the perspective of denoising.

Auditory steady state responses (ASSRs) in cochlear implant (CI) patients are contaminated by the spread of a continuous CI electrical stimulation artifact. The aim of this work was to model the electrophysiological mixture of the CI artifact and the corresponding evoked potentials on scalp electrodes in order to evaluate the performance of denoising algorithms in eliminating the CI artifact in a controlled environment. The basis of the proposed computational framework is a neural mass model representing the nodes of the auditory pathways. Six main contributors to auditory evoked potentials from the cochlear level and up to the auditory cortex were taken into consideration. The simulated dynamics were then projected into a 3-layer realistic head model. 32-channel scalp recordings of the CI artifact-response were then generated by solving the electromagnetic forward problem. As an application, the framework's simulated 32-channel datasets were used to compare the performance of 4 commonly used Independent Component Analysis (ICA) algorithms: infomax, extended infomax, jade and fastICA in eliminating the CI artifact. As expected, two major components were detectable in the simulated datasets, a low frequency component at the modulation frequency and a pulsatile high frequency component related to the stimulation frequency. The first can be attributed to the phase-locked ASSR and the second to the stimulation artifact. Among the ICA algorithms tested, simulations showed that infomax was the most efficient and reliable in denoising the CI artifact-response mixture. Denoising algorithms can induce undesirable deformation of the signal of interest in real CI patient recordings. The proposed framework is a valuable tool for evaluating these algorithms in a controllable environment ahead of experimental or clinical applications.

Criteria versus guidelines: Are we doing the best for our paediatric patients?

The National Institute for Health and Care Excellence guidance for the provision of cochlear implants (NICE Technology Appraisal Guidance 166. Cochlear implants for children and adults with severe to profound deafness. 2009. National Health Service National Institute for Health and Clinical Excellence.) are used to develop candidacy criteria by public health funding bodies within the UK. Often the guidance is interpreted as strict 'criteria' whereby clinicians adhere to specific audiometric thresholds without accounting for the acceptable range of performance on individual tests or a child's functional development. In this paper four clinical paediatric case studies are described from two cochlear implant centres which serve to illustrate difficulties in applying NICE guidance as strict criteria. These are presented in the context of recommending more flexible interpretation based on the content of the current guidance along with considerations of circumstances where NICE guidance might be adapted to optimise use of cochlear implant technology within a national framework.

Evaluation of focused multipolar stimulation for cochlear implants in acutely deafened cats.

OBJECTIVE: The conductive nature of the fluids and tissues of the cochlea can lead to broad activation of spiral ganglion neurons using contemporary cochlear implant stimulation configurations such as monopolar (MP) stimulation. The relatively poor spatial selectivity is thought to limit implant performance, particularly in noisy environments. Several current focusing techniques have been proposed to reduce the spread of activation with the aim towards achieving improved clinical performance. APPROACH: The present research evaluated the efficacy of focused multipolar (FMP) stimulation, a relatively new focusing technique in the cochlea, and compared its efficacy to both MP stimulation and tripolar (TP) stimulation. The spread of neural activity across the inferior colliculus (IC), measured by recording the spatial tuning curve, was used as a measure of spatial selectivity. Adult cats (n = 6) were acutely deafened and implanted with an intracochlear electrode array before multi-unit responses were recorded across the cochleotopic gradient of the contralateral IC. Recordings were made in response to acoustic and electrical stimulation using the MP, TP and FMP configurations. MAIN RESULTS: FMP and TP stimulation resulted in greater spatial selectivity than MP stimulation. However, thresholds were significantly higher (p < 0.001) for FMP and TP stimulation compared to MP stimulation. There were no differences found in spatial selectivity and threshold between FMP and TP stimulation. SIGNIFICANCE: The greater spatial selectivity of FMP and TP stimulation would be expected to result in improved clinical performance. However, further research will be required to demonstrate the efficacy of these modes of stimulation after longer durations of deafness.

Analysis of cochlear implant artifact removal techniques using the continuous wavelet transform.

When patients with cochlear implants (CI) undergo cortical auditory evoked potential (CAEP) tests to evaluate their hearing, a large electrical artifact introduced by the CI obscures the relevant information in the signal. Several methods have been developed for the purpose of removing the CI artifact; however, there is no gold standard (i.e., patient's auditory response before the CI) to assess the effectiveness of these methods in terms of successful removal of artifact. To address this crucial shortcoming, we employ time-frequency (TF) signal representation (i.e., continuous wavelet transform (CWT)) to evaluate the effectiveness of two recent CI removal techniques, known as the subtraction and polynomial methods. Our results show that polynomial method consistently outperforms the subtraction method in the presence of tone stimulus. These results also indicate a possible CWT-based method for removing the CI artifact from a speech stimuli response, which the subtraction and polynomial methods cannot do.

Use of an adaptive-bandwidth protocol to measure importance functions for simulated cochlear implant frequency channels.

The Articulation Index and Speech Intelligibility Index predict intelligibility scores from measurements of speech and hearing parameters. One component in the prediction is the frequency-importance function, a weighting function that characterizes contributions of particular spectral regions of speech to speech intelligibility. The purpose of this study was to determine whether such importance functions could similarly characterize contributions of electrode channels in cochlear implant systems. Thirty-eight subjects with normal hearing listened to vowel-consonant-vowel tokens, either as recorded or as output from vocoders that simulated aspects of cochlear implant processing. Importance functions were measured using the method of Whitmal and DeRoy [J. Acoust. Soc. Am. 130, 4032-4043 (2011)], in which signal bandwidths were varied adaptively to produce specified token recognition scores in accordance with the transformed up-down rules of Levitt [J. Acoust. Soc. Am. 49, 467-477 (1971)]. Psychometric functions constructed from recognition scores were subsequently converted into importance functions. Comparisons of the resulting importance functions indicate that vocoder processing causes peak importance regions to shift downward in frequency. This shift is attributed to changes in strategy and capability for detecting voicing in speech, and is consistent with previously measured data.

Timbre discrimination in cochlear implant users and normal hearing subjects using cross-faded synthetic tones.

The identification and discrimination of timbre are essential features of music perception in cochlear implant users. As timbre differences appear as multidimensional cues, the spectral shape, the spectral fluctuation, and the rise time are the most dominating parameters of timbre in normal hearing listeners. Recently, a psychoacoustical test was developed to determine the timbre discrimination abilities using only the spectral shape difference as a cue. Therefore, a synthetically generated tone continuum was used in an adaptive alternative forced choice paradigm. The spectral shape was modified by cross-fading the tones adaptively, depending on the listeners' response which allows very precise determinations of the just noticeable difference (JND). With this behavioral test, the spectral shape JND for complex tones with different fundamental frequencies was measured in cochlear implant users and compared to normal hearing listeners. The results confirm the applicability of the test to measure timbre discrimination in cochlear implant users. The resulting individual spectral shape JND profiles reveal a maximum with a fundamental frequency of 525 Hz, whereas the JND profiles were rather flat in the normal hearing individuals.

Cochlear implant patients' speech understanding in background noise: effect of mismatch between electrode assigned frequencies and perceived pitch.

OBJECTIVE: To assess the electrode pitch function in a series of adults with postlingually implanted cochlear implants and with contralateral residual hearing, in order to investigate the correlation between the degree of frequency map mismatch and the subjects' speech understanding in quiet and noisy conditions. DESIGN: Case series. SUBJECTS: Seven postlingually deafened adults with cochlear implants, all with detectable contralateral residual hearing. Subjects' electrode pitch function was assessed by means of a pitch-matching test, in which they were asked to match an acoustic pitch (pure tones delivered to the non-implanted ear by an audiometer) to a perceived 'pitch' elicited by stimulation of the cochlear implant electrodes. A mismatch score was calculated for each subject. Speech recognition was tested using lists of sentences presented in quiet conditions and at +10, 0 and 5 dB HL signal-to-noise ratio levels (i.e. noise 10 dB HL lower than signal, noise as loud as signal and noise 5 dB HL higher than signal, respectively). Correlations were assessed using a linear regression model, with significance set at p < 0.05. RESULTS: All patients presented some degree of mismatch between the acoustic frequencies assigned to their implant electrodes and the pitch elicited by stimulation of the same electrode, with high between-individual variability. A significant correlation (p < 0.005) was found between mismatch and speech recognition scores at +10 and 0 dB HL signal-to-noise ratio levels (r2 = 0.91 and 0.89, respectively). CONCLUSION: The mismatch between frequencies allocated to electrodes and the pitch perceived on stimulation of the same electrodes could partially account for our subjects' difficulties with speech understanding in noisy conditions. We suggest that these subjects could benefit from mismatch correction, through a procedure allowing individualised reallocation of frequency bands to electrodes.

Acoustic to electric pitch comparisons in cochlear implant subjects with residual hearing.

The aim of this study was to assess the frequency-position function resulting from electric stimulation of electrodes in cochlear implant subjects with significant residual hearing in their nonimplanted ear. Six cochlear implant users compared the pitch of the auditory sensation produced by stimulation of an intracochlear electrode to the pitch of acoustic pure tones presented to their contralateral nonimplanted ear. Subjects were implanted with different Clarion electrode arrays, designed to lie close to the inner wall of the cochlea. High-resolution radiographs were used to determine the electrode positions in the cochlea. Four out of six subjects presented electrode insertions deeper than 450 degrees . We used a two-interval (one acoustic, one electric), two-alternative forced choice protocol (2I-2AFC), asking the subject to indicate which stimulus sounded the highest in pitch. Pure tones were used as acoustic stimuli. Electric stimuli consisted of trains of biphasic pulses presented at relatively high rates [higher than 700 pulses per second (pps)]. First, all electric stimuli were balanced in loudness across electrodes. Second, acoustic pure tones, chosen to approximate roughly the pitch sensation produced by each electrode, were balanced in loudness to electric stimuli. When electrode insertion lengths were used to describe electrode positions, the pitch sensations produced by electric stimulation were found to be more than two octaves lower than predicted by Greenwood's frequency-position function. When insertion angles were used to describe electrode positions, the pitch sensations were found about one octave lower than the frequency-position function of a normal ear. The difference found between both descriptions is because of the fact that these electrode arrays were designed to lie close to the modiolus. As a consequence, the site of excitation produced at the level of the organ of Corti corresponds to a longer length than the electrode insertion length, which is used in Greenwood's function. Although exact measurements of the round window position as well as the length of the cochlea could explain the remaining one octave difference found when insertion angles were used, physiological phenomena (e.g., stimulation of the spiral ganglion cells) could also create this difference. From these data, analysis filters could be determined in sound coding strategies to match the pitch percepts elicited by electrode stimulation. This step might be of main importance for music perception and for the fitting of bilateral cochlear implants.

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. Radiographic analyses found that the Contour array lay closer to the modiolus, was more deeply inserted and spanned a larger fractional length of the basilar membrane than the straight banded-electrode array. The results were analysed in terms of array type and of the position of the individual electrode band, both distance from the modiolus and longitudinal placement. Mean threshold was lower for the Contour array but maximum comfortable level was similar. Whereas threshold varied significantly with distance of electrode band from the modiolus, maximum comfortable level did not. Pitch varied fairly regularly with longitudinal position of the stimulated electrode, with the exception of one Contour subject. The forward masking profiles, using moderately loud maskers, were narrower for the Contour array, indicative of more localized neural excitation.

Are cochlear implant patients suffering from perceptual dissonance?

Cochlear implants provide functional hearing to the majority of recipients and have gained widespread acceptance clinically, but the range of performance remains great and largely unexplained. Designs for implanted electrodes and electronics have converged, whereas novel speech processing strategies have proliferated. For each patient, the fitting audiologist must sort empirically through options that produce large but idiosyncratic differences in both objective performance and subjective preference. This review and analysis suggests that the place-pitch and rate-pitch theories on which cochlear implants have been designed are incomplete. The missing component may be related to the phase-locking of auditory nerve activity to both acoustic and electrical stimulation. This component is likely to be highly distorted by electrical stimulation but its importance as one of several different pitch encoding mechanisms may vary widely among patients. Systematic means to control these putative phase effects using modern, high-speed, and high-density cochlear implants may make it possible to identify more efficiently the best strategy for a given patient and to minimize the perceptual confusion that arises from conflicting cues.

Chronic depolarization enhances the trophic effects of brain-derived neurotrophic factor in rescuing auditory neurons following a sensorineural hearing loss.

The development and maintenance of spiral ganglion neurons (SGNs) appears to be supported by both neural activity and neurotrophins. Removal of this support leads to their gradual degeneration. Here, we examined whether the exogenous delivery of the neurotrophin brain-derived neurotrophic factor (BDNF) in concert with electrical stimulation (ES) provides a greater protective effect than delivery of BDNF alone in vivo. The left cochlea of profoundly deafened guinea pigs was implanted with an electrode array and drug-delivery system. BDNF or artificial perilymph (AP) was delivered continuously for 28 days. ES induced neural activity in two cohorts (BDNF/ES and AP/ES), and control animals received BDNF or AP without ES (BDNF/- and AP/-). The right cochleae of the animals served as deafened untreated controls. Electrically evoked auditory brainstem responses (EABRs) were recorded immediately following surgery and at completion of the drug-delivery period. AP/ES and AP/- cohorts showed an increase in EABR threshold over the implantation period, whereas both BDNF cohorts exhibited a reduction in threshold (P < 0.001, t-test). Changes in neural sensitivity were complemented by significant differences in both SGN survival and soma area. BDNF cohorts demonstrated a significant trophic or survival advantage and larger soma area compared with AP-treated and deafened control cochleae; this advantage was greatest in the base of the cochlea. ES significantly enhanced the survival effects of BDNF throughout the majority of the cochlea (P < 0.05, Bonferroni's t-test), although there was no evidence of trophic support provided by ES alone. Cotreatment of SGNs with BDNF and ES provides a substantial functional and trophic advantage; this treatment may have important implications for neural prostheses.

A comparison of the speech understanding provided by acoustic models of fixed-channel and channel-picking signal processors for cochlear implants.

Vowels, consonants, and sentences were processed by two cochlear-implant signal-processing strategies-a fixed-channel strategy and a channel-picking strategy-and the resulting signals were presented to listeners with normal hearing for identification. At issue was the number of channels of stimulation needed in each strategy to achieve an equivalent level of speech recognition in quiet and in noise. In quiet, 8 fixed channels allowed a performance maximum for the most difficult stimulus material. A similar level of performance was reached with a 6-of-20 channel-picking strategy. In noise, 10 fixed channels allowed a performance maximum for the most difficult stimulus material. A similar level of performance was reached with a 9-of-20 strategy. Both strategies are capable of providing a very high level of speech recognition. Choosing between the two strategies may, ultimately, depend on issues that are independent of speech recognition-such as ease of device programming.

Pitch comparisons of acoustically and electrically evoked auditory sensations.

Cochlear implant users with some residual hearing in the non-implanted ear compared the pitch sensations produced by acoustic pure tones and pulsatile electric stimuli. Pitch comparisons were obtained for pure tones and electrical stimuli presented at different positions (electrodes) in the scala tympani, keeping the electric pulse rate fixed at 100, 250, or 800 pps. Similarly, pitch comparisons were obtained for electrical stimuli with variable pulse rates presented to two fixed electrode positions (apical and basal) in the cochlea. Both electrode position and pulse rate influenced the perceived pitch of the electrical signal and 'matched' electric and acoustic signals were found over a wide range of frequencies. There was a large variation between listeners. For some stimuli, listeners had difficulty in deciding whether the acoustic or electric stimulus was higher in pitch. Despite the variability, consistent trends were obtained from the data: higher frequencies tended to be matched by more basal electrodes for all pulse rates. Higher frequencies tended to be matched by higher pulse rates for both electrode positions. The electrode positions that 'matched' pure tones were more basal than predicted from the characteristic frequency coordinates of the basilar membrane in a normal human cochlea.

The acoustic two-tone distortions 2f1-f2 and f2-f1 and their possible relation to changes in the operating point of the cochlear amplifier.

Acoustic two-tone distortions are generated during non-linear mechanical amplification in the cochlea. Generation of the cubic distortion 2f1-f2 depends on asymmetric components of a non-linear transfer function whereas the difference tone f2-f1 relies on symmetric components. Therefore, a change of the operating point and hence the symmetry of the cochlear amplifier could be strongly reflected in the level of the f2-f1 distortion. To test this hypothesis, low-frequency tones (5 Hz) were used to bias the position of the cochlear partition in the gerbil. Phase-correlated changes of f2-f1 occurred at bias tone levels where there were almost no effects on 2f1-f2. Higher levels of the bias tone induced pronounced changes of both distortions. These results are qualitatively in good agreement with the results of a simulation in which the operating point of a Boltzman function was shifted. This function is similar to those used to describe outer hair cell (OHC) transduction. To influence OHC motility, salicylate was injected. It caused a decrease of the 2f1-f2 level and an increase in the level of f2-f1. Such reciprocal changes of both distortions, again, can be interpreted in terms of a shift of the operating point of the cochlear amplifier along a non-linear transfer characteristic. To directly influence the cochlear amplifier, DC current was injected into the scala media. Large negative currents (> -2 microA) caused a pronounced decrease of 2f1-f2 (> 15 dB) and positive currents had more complex effects with increasing and/or decreasing 2f1-f2 distortion level. The effects were time and primary level dependent. Changes of f2-f1 for DC currents > magnitude of mu 2A were in most cases larger compared to 2f1-f2 and reversed for certain primary levels. The current effects probably result from a combination of changing the endocochlear potential and shifting the operating point along a non-linear transfer function.

Pitch perception in patients with a multi-channel cochlear implant using various pulses width.

Cochlear implants have been designed to partially restore hearing to those people who are totally deaf. Multi-channel cochlear implants offer the opportunity to evoke acoustic perceptions like loudness and pitch, elicited by a controllable pattern of electric stimulation by means of electrodes placed in different places along the cochlear length. In this study, two psychophysical experiments were conducted with 4 patients, 1 prelingually and 3 postlingually-deafened, implanted with the multi-channel cochlear prosthesis Nucleus 22. Experiments were carried out to study the effect of varying the width of the electric biphasic pulsatile stimuli on the discriminative abilities of the pitch perception. The tests involved place pitch ranking and pulse rate discrimination. Place pitch ranking was studied by determining the just noticeable difference in pitch pairs (jnd-pp), defined as the pair of nearest electrodes which elicit different pitch perception. Pulse rate discrimination was studied by determining the just noticeable difference in pulse rate (jnd-pr) defined as the minimal difference in stimulus repetition rate over a given electrode, which elicits different pitch perceptions. Both experiments were conducted using pulses of 400, 200, 100 and 50 microseconds/phase. The results indicated that in spite of the differences in pathologies and personal histories, both jnd-pp and jnd-pr decrease by diminishing the pulse width. Speech perceptual data, measured for various pulse widths, validates the usefulness of decreased pulse width which yields favorable results in the psychophysical tests.

PC analysis of altered speech respiration following fitting of a multi-channel cochlear implant prosthesis.

This paper describes a personal computer (PC) application for speech respiration analysis. Parameters that can be determined include lung volume changes, the relative contributions of the rib cage and abdomen to lung volume changes and the configuration of the chest wall during speech production. Data collected from two subjects fitted with Nucleus cochlear implant prostheses illustrate one application of this technique. The PC based kinematic analysis described provides previously inaccessible information about the effects of changes in the level of auditory feedback resulting from activation of a multiple channel cochlear prosthesis on the speech production mechanism.