Richard C. Dowell

Clinical findings for a group of infants and young children with auditory neuropathy

OBJECTIVE To examine the prevalence of auditory neuropathy in a group of infants at risk for hearing impairment and to present an overview of the clinical findings for affected children. DESIGN Results for 20 subjects who showed repeatable cochlear microphonic potentials in the absence of click-evoked auditory brain stem responses are included in this study. Behavioral and steady state evoked potential thresholds were established in each case. Where possible, otoacoustic emission and speech perception results (unaided and aided) also were obtained. RESULTS One in 433 (0.23%) of the children in our series had evidence of auditory neuropathy. The audiometric findings for these subjects varied significantly, with behavioral thresholds ranging from normal to profound levels. Discrimination skills were also variable. Approximately half of the subjects showed little understanding, or even awareness, of speech inputs in both the unaided and aided conditions. There were, however, a number of children who could score at significant levels on speech discrimination tasks and who benefited from the provision of amplification. CONCLUSION The results suggest that auditory neuropathy is more common in the infant population than previously suspected. The effects of neuropathy on auditory function appear to be idiosyncratic, producing significant variations in both the detection and discrimination of auditory signals. As such, the management of children with this disorder must allow for individual differences.

Speech perception and cortical event related potentials in children with auditory neuropathy.

Objectives 1) To investigate the unaided and aided speech perception abilities of children with auditory neuropathy (AN) and to compare their performance to children with sensorineural hearing loss. 2) To establish whether cortical event related potentials (ERPs) could be recorded in children with AN, and to determine the relationship between the presence of these responses and speech perception. Design Unaided and aided speech perception assessments (PBK words), and cortical-ERP testing was carried out in a group of 18 children with AN. Data also were obtained from a cohort of age and hearing level matched children with sensorineural hearing loss. Results The speech perception performance of the 15 children with AN able to complete a PBK-word assessment, fell into two distinct categories. The children either showed no open-set speech perception ability (7/15 cases), or performance levels similar to their sensorineural counterparts (8/15 cases). Approximately 50% of children with AN showed ERPs of normal latency, amplitude and morphology. In all cases, response presence (at normal latencies) was consistent with reasonable speech perception ability, and response absence was consistent with negligible speech perception. Conclusions In approximately 50% of children with auditory neuropathy, the provision of amplification results in significant open-set speech perception improvements. The results confirm the previously published reports that speech perception ability cannot be reliably estimated from the behavioral audiogram in children with AN. Obligatory ERP test results may offer a means of predicting perceptual skills in newly diagnosed youngsters as the presence of ERPs (with age-appropriate latency and morphology) was correlated with significant open set speech perception abilities and amplification benefit. The absence of the ERP in contrast, indicated profound hearing disability evidenced by profound hearing loss and/or extremely poor speech perception.

Factors predicting postoperative sentence scores in postlinguistically deaf adult cochlear implant patients

A sample of 64 postlinguistically profoundly to totally deaf adult cochlear implant patients were tested without lipreading by means of the Central Institute for the Deaf (CID) sentence test 3 months postoperatively. Preoperative promontory stimulation results (thresholds, gap detection, and frequency discrimination), age, duration of profound deafness, cause of deafness, lipreading ability, postoperative intracochlear thresholds and dynamic ranges for electrical stimulation, depth of insertion of the electrode array into the scala tympani, and number of electrodes in use were considered as possible factors that might be related to the postoperative sentence scores. A multiple regression analysis with stepwise inclusion of independent variables indicated that good gap detection and frequency discrimination during preoperative promontory testing, larger numbers of electrodes in use, and greater dynamic ranges for intracochlear electrical stimulation were associated with better CID scores. The CID scores tended to decrease with longer periods of profound deafness.

Factors Affecting Auditory Performance of Postlinguistically Deaf Adults Using Cochlear Implants: An Update with 2251 Patients

Objective: To update a 15-year-old study of 800 postlinguistically deaf adult patients showing how duration of severe to profound hearing loss, age at cochlear implantation (CI), age at onset of severe to profound hearing loss, etiology and CI experience affected CI outcome. Study Design: Retrospective multicenter study. Methods: Data from 2251 adult patients implanted since 2003 in 15 international centers were collected and speech scores in quiet were converted to percentile ranks to remove differences between centers. Results: The negative effect of long duration of severe to profound hearing loss was less important in the new data than in 1996; the effects of age at CI and age at onset of severe to profound hearing loss were delayed until older ages; etiology had a smaller effect, and the effect of CI experience was greater with a steeper learning curve. Patients with longer durations of severe to profound hearing loss were less likely to improve with CI experience than patients with shorter duration of severe to profound hearing loss. Conclusions: The factors that were relevant in 1996 were still relevant in 2011, although their relative importance had changed. Relaxed patient selection criteria, improved clinical management of hearing loss, modifications of surgical practice, and improved devices may explain the differences.

Steady-state evoked potential and behavioral hearing thresholds in a group of children with absent click-evoked auditory brain stem response

Objective: 1) To examine the distribution of behavioral hearing thresholds in a group of children who had shown no click‐evoked auditory brain stem response (ABR) at maximum presentation levels. 2) To describe the relationship between the 90 Hz steady‐state evoked potential (SSEP) and behavioral thresholds in these subjects. Design: A retrospective study based on clinical findings obtained from 108 infants and young children. Each of these children had shown no recordable ABR to clicks presented at maximum levels (100 dB nHL). SSEP audiograms were obtained using AM/FM tones at the octave frequencies 250 to 4000 Hz. The results of these evoked potential assessments were compared with hearing thresholds established behaviorally. Results: Click‐ABR assessment could not differentiate between the subjects in our sample with total hearing losses and those with useful residual hearing. Although some of the ears were anacusic, more than a quarter showed residual hearing at each of the audiometric frequencies. Furthermore, at least 10% of the behavioral thresholds at each frequency fell within the moderate/severe hearing loss range. A far closer relationship was observed between SSEP and hearing thresholds. On occasions where the SSEP was absent at maximum levels, 99.5% of the ears showed either a total loss or a behavioral threshold within 10 dB of that level. When an SSEP was obtained, the hearing threshold was typically within 5 dB of the SSEP threshold. Conclusion: The results suggested that in our group of selected subjects, the SSEP technique was able to assess ears with only minimal amounts of residual hearing. Where the brevity of the acoustic click limits both its frequency specificity and its presentation level, the modulated tones used for SSEP testing allow accurate, frequency‐specific assessment at high presentation levels.

Variation in speech perception scores among children with cochlear implants.

Objective The objective of this study was to identify common factors affecting speech perception scores in children with cochlear implants. Design Speech perception data for 167 implanted children were collected at two cochlear implant centres in Melbourne and Sydney. The data comprised audition-alone scores on open-set word and sentence tests. Children were selected on the basis that they had a Nucleus 22-electrode cochlear implant. The average age of the children was 5 yr. Information was also collected about 12 factors that may have influenced speech perception scores for each child. Analysis of covariance was used to identify factors that significantly affected speech perception scores. Pearson pairwise correlation coefficients were also calculated for all factors analyzed. Results The analyses in this study identified factors that accounted for 51%, 34%, and 45% of the variance in phoneme, word and sentence perception scores. Scores decreased by 1.4 to 2.4% per year of profound deafness prior to implantation. Children who normally use oral communication scored significantly higher than children normally using sign or simultaneous oral and sign communication. Children implanted in Sydney scored higher on average than children implanted in Melbourne. Conclusions The results show that a significant part of the variation in speech perception scores is systematically related to audiological and environmental factors for each child. The reasons for significant differences between children using different communication modes or from different clinics were not identified.

Pre-, Per- and Postoperative Factors Affecting Performance of Postlinguistically Deaf Adults Using Cochlear Implants: A New Conceptual Model over Time

Objective To test the influence of multiple factors on cochlear implant (CI) speech performance in quiet and in noise for postlinguistically deaf adults, and to design a model of predicted auditory performance with a CI as a function of the significant factors. Study Design Retrospective multi-centre study. Methods Data from 2251 patients implanted since 2003 in 15 international centres were collected. Speech scores in quiet and in noise were converted into percentile ranks to remove differences between centres. The influence of 15 pre-, per- and postoperative factors, such as the duration of moderate hearing loss (mHL), the surgical approach (cochleostomy or round window approach), the angle of insertion, the percentage of active electrodes, and the brand of device were tested. The usual factors, duration of profound HL (pHL), age, etiology, duration of CI experience, that are already known to have an influence, were included in the statistical analyses. Results The significant factors were: the pure tone average threshold of the better ear, the brand of device, the percentage of active electrodes, the use of hearing aids (HAs) during the period of pHL, and the duration of mHL. Conclusions A new model was designed showing a decrease of performance that started during the period of mHL, and became faster during the period of pHL. The use of bilateral HAs slowed down the related central reorganization that is the likely cause of the decreased performance.

Performance of postlinguistically deaf adults with the Wearable Speech Processor (WSP III) and Mini Speech Processor (MSP) of the Nucleus Multi-Electrode Cochlear Implant.

Seven postlinguistically deaf adults implanted with the Nucleus Multi-Electrode Cochlear Implant participated in an evaluation of speech perception performance with three speech processors: the Wearable Speech Process (WSP III), a prototype of the Mini Speech Processor, and the Mini Speech Processor. The first experiment was performed with the prototype and Wearable Speech Processor both programmed using the F0F1F2 speech coding strategy. The second experiment compared performance with the Mini Speech Processor programmed with the Multi-Peak speech coding strategy and the Wearable Speech Processor programmed with the F0F1F2 speech coding strategy. Performance was evaluated in the sound-only condition using recorded speech tests presented in quiet and in noise. Questionnaires and informal reports provided information about use in everyday life. In experiment I, there was no significant difference in performance using the Wearable Speech Processor and prototype on any of the tests. Nevertheless, six out of seven subjects preferred the prototype for use in everyday life. In experiment II, performance on open-set tests in quiet and noise was significantly higher with the Mini Speech Processor (Multi-Peak speech coding strategy) than with the Wearable Speech Processor. Subjects reported an increase in their ability to communicate with other people using the Mini Speech Processor (Multi-Peak speech coding strategy) compared with the Wearable Speech Processor in everyday life.

Psychophysical studies evaluating the feasibility of a speech processing strategy for a multiple-channel cochlear implant

This paper reports further psychophysical studies on a multiple-channel cochlear implant patient evaluating the feasibility of a speech processing strategy which converts the acoustic fundamental frequency to electric repetition rate, the second-formant frequency to electrode position, and the acoustic amplitude to current level. The first four studies evaluated the use of a special pulse pattern to minimize the loudness variation with electric repetition rate. The chosen pulse pattern consisted of multiple pulses occurring in the first half of each repetitive period (MPP) in contrast to the more conventional pattern with a single pulse per period (SPP). The results showed that MPP approximately equalized the loudness variation with repetition rate. The dynamic range of current, the pitch variation with repetition rate, and the difference limens for repetition rate were found to be similar to MPP and SPP. Two other studies investigated interaction between electrode position and repetition rate (RR). The first of these showed that the patient could make use of information provided by rising or falling RR trajectories superimposed on individual electrodes or electrode trajectories as an indicator of the direction of intonation variation. The second of these studies showed that the dissimilarities amongst the hearing sensations produced by steady-state stimuli differing in electrode position and repetition rate were characterized by two perceptual components, relating to the two electric parameters, respectively.

Psychophysical studies for two multiple-channel cochlear implant patients.

Psychophysical studies were conducted on two multiple-channel cochlear implant patients to examine the nature of the hearing sensations produced by electrical stimulation of auditory nerve fibers using electrodes at different sites in the scala tympani (one electrode at a time). Both time-invariant stimuli, whose parameter values did not vary in time, and time-varying stimuli, specified by a linear variation in parameter values, were used. A sharpness ranking study using time-invariant signals suggested that the hearing sensations produced by different electrodes varied from dull to sharp in an apical to basal direction in the scala tympani. A categorization study showed that the hearing sensations produced by two adjacent electrodes (1.5 mm apart) were rarely confused for a restricted range of time-invariant pulse rates. Discriminability studies by a same-different procedure for stimuli with pulse rate below 250 pps showed: (1) relative difference limens of 6% to 12% for time-invariant pulse rates, and 9% and 13% for time-varying pulse rates; (2) stimuli with time-varying electrode position differing in the direction of electrode trajectory were readily discriminated; and (3) the discrimination of time-varying pulse rates deteriorated with decreases in the duration of the variation, while the discriminability of single-electrode trajectories was the same for the three durations: 25, 50, and 100 ms. A speech processing strategy was also proposed on the bases of these results.