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 Cochlear's 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 Smart Sound 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 Cochlear's 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.

The Effect of Hearing Aid Use on Cognition in Older Adults: Can We Delay Decline or Even Improve Cognitive Function?

Hearing loss is a modifiable risk factor for dementia in older adults. Whether hearing aid use can delay the onset of cognitive decline is unknown. Participants in this study (aged 62–82 years) were assessed before and 18 months after hearing aid fitting on hearing, cognitive function, speech perception, quality of life, physical activity, loneliness, isolation, mood, and medical health. At baseline, multiple linear regression showed hearing loss and age predicted significantly poorer executive function performance, while tertiary education predicted significantly higher executive function and visual learning performance. At 18 months after hearing aid fitting, speech perception in quiet, self-reported listening disability and quality of life had significantly improved. Group mean scores across the cognitive test battery showed no significant decline, and executive function significantly improved. Reliable Change Index scores also showed either clinically significant improvement or stability in executive function for 97.3% of participants, and for females for working memory, visual attention and visual learning. Relative stability and clinically and statistically significant improvement in cognition were seen in this participant group after 18 months of hearing aid use, suggesting that treatment of hearing loss with hearing aids may delay cognitive decline. Given the small sample size, further follow up is required.

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.

The Effect of Cochlear Implants on Cognitive Function in Older Adults: Initial Baseline and 18-Month Follow Up Results for a Prospective International Longitudinal Study

In older adults, hearing loss is independently associated with an increased rate of cognitive decline, and has been identified to be a modifiable risk factor for dementia. The mechanism underlying the cognitive decline associated with hearing loss is not understood, but it is known that the greater the hearing loss, the faster the rate of decline. It is unknown whether remediation of hearing loss with hearing devices can delay cognitive decline. This 5-year international longitudinal study is investigating the impact of cochlear implants on cognitive function in older people with severe-profound hearing loss, and whether remediation of hearing loss could delay the onset of cognitive impairment. This is the first study to examine the major primary risk factors associated with dementia in the same cohort. Participants were assessed before cochlear implantation and 18 months later using an identical battery including a visually presented cognitive assessment tool (Cogstate battery) that is highly sensitive to small changes in cognition and suitable for use with people with hearing loss. Hearing and speech perception ability were assessed in sound-treated conditions by an audiologist, and a range of questionnaire tools was administered to assess self-perceived ease of listening, quality of life, physical activity, diet, social and emotional loneliness, isolation, anxiety, and depression. A detailed medical health history was taken. Pre-operatively, despite the small initial sample size (n = 59), increased hearing loss and age predicted significantly poorer executive function and visual attention, while tertiary education predicted better executive function. Better self-reported quality of life was correlated with better visual learning performance, and engaging in frequent vigorous physical activity was correlated with poorer visual learning performance. At 18 months, for the first 20 participants, significant benefits of cochlear implants were seen in terms of speech perception, communication ability, and quality of life. Multiple linear regression modeling showed executive function improved significantly for non-tertiary educated males, while cognitive function remained stable for other participants. Further follow-up at 18 month intervals with a larger sample will reveal the effects of cochlear implant intervention on all outcomes, and whether this can delay cognitive decline.

Pitch perception for different modes of stimulation using the cochlear multiple-electrode prosthesis

Numerical estimations of pitch were obtained from nine postlinguistically deafened adults using the 22-electrode cochlear implant manufactured by Cochlear Pty. Limited. A series of electrodes on the array were stimulated using three modes of stimulation: Bipolar (BP), common ground (CG), and monopolar (MONO). In BP stimulation, an electric current was passed between two electrodes separated by one electrode for eight patients and two electrodes for one patient. In CG stimulation, a single electrode was activated and the other electrodes on the array were connected together to serve as the return path for the current. In MONO stimulation, an electric current was passed between a single electrode and the most basal electrode on the array. Pitch estimations were generally consistent with the tonotopic organization of the cochlea. There was a marked reversal in pitch for electrodes in the middle of the array using CG stimulation for three patients. A reduced range of pitch using MONO stimulation was recorded for patients where the most basal electrode was internal to the cochlea. There were also individual differences in pitch estimations between the three modes of stimulation for most patients. The current levels required to elicit threshold (T) and comfortable listening (C) levels were, in general, higher for BP stimulation than for CG stimulation and were lowest for MONO stimulation. For CG stimulation, there was a tendency for T and C levels to be higher for electrodes in the middle of the array than at the basal or apical ends. For MONO stimulation, T and C levels uniformly increased in an apical to basal direction for the majority of patients. There was no consistent pattern in T and C levels for BP stimulation. The size of the range of usable hearing using CG stimulation tended to be similar to that using BP stimulation and was usually higher than that using MONO stimulation.

Gap detection by early-deafened cochlear-implant subjects

Two studies investigating gap-detection thresholds were conducted with cochlear-implant subjects whose onset of profound hearing loss was very early in life. The Cochlear Limited multiple-electrode prosthesis was used. The first study investigated the effects of pulse rate (200, 500, and 1000 pulses/s) and stimulus duration (500 and 1000 ms) on gap thresholds in 15 subjects. Average gap thresholds were 1.8 to 32.1 ms. There was essentially no effect of pulse rate and for almost all subjects, no effect of stimulus duration. For two subjects, performance was poorer for the 1000-ms stimulus duration. The second study investigated the relationships between gap thresholds, subject variables, and speech-perception scores. Data from the first study were combined with those from previous studies [Busby et al., Audiology 31, 95-111 (1992); Tong et al., J. Acoust. Soc. Am. 84, 951-962 (1988)], providing data from 27 subjects. A significant negative correlation was found between age at onset of deafness and gap thresholds and most variability in gap thresholds was for the congenitally deaf subjects. Significant negative correlations were found between gap thresholds and word scores for open-set Bamford-Kowal-Bench (BKB) sentences in the auditory-visual condition and lipreading enhancement scores for the same test.

The perception of temporal modulations by cochlear implant patients

The perception of temporal modulations of pulsatile electric stimuli was measured in seven cochlear implant patients using the Cochlear Pty. Limited prosthesis. Four patients were postlingually deafened adults and three patients were young adults who were deafened very early in life. The first study measured detection thresholds for modulated pulse duration for a series of modulation frequencies and pulse rates. The shape of the detection thresholds as a function of modulation frequency, the temporal modulation transfer function, often resembled a low-pass filter with a 50-100-Hz cut-off frequency. Thresholds did not markedly vary across the different pulse rates for most patients. Thresholds were less than 10%-20% of the range of usable hearing for most patients. The second study compared detection thresholds for modulated pulse durations around different reference pulse durations: 50, 100, and 300 microseconds. Detection thresholds were generally proportional to the different reference pulse durations. The third study measured difference limens for the discrimination of modulation depth. The difference limens were similar to the detection thresholds for the same reference pulse duration and pulse rate. The three patients deafened very early in life showed more within-group variation in performance, and their overall levels of performance were poorer than those of the postlingually deafened adults.

Short-term auditory memory in children using cochlear implants and its relevance to receptive language

The aim of this study was to assess auditory sequential, short-term-memory (SSTM) performance in young children using cochlear implants (CI group) and to examine the relationship of this performance to receptive language performance. Twenty-four children, 5 to 11 years old, using the Nucleus 22-electrode cochlear implant, were tested on a number of auditory and visual tasks of SSTM. The auditory memory tasks were designed to minimize the effect of auditory discrimination ability. Stimuli were chosen that children with cochlear implants could accurately identify with a reaction time similar to that of a control group of children with normal hearing (NH group). All children were also assessed on a receptive language test and on a nonverbal intelligence scale. As expected, children using cochlear implants demonstrated poorer auditory and visual SSTM skills than their hearing peers when the stimuli were verbal or were pictures that could be readily labeled. They did not differ from their peers with normal hearing on tasks where the stimuli were less likely to be verbally encoded. An important finding was that the CI group did not appear to have a sequential memory deficit specific to the auditory modality. The difference scores (auditory minus visual memory performance) for the CI group were not significantly different from those for the NH group. SSTM performance accounted for significant variance in the receptive language performance of the CI group. However, a forward stepwise regression analysis revealed that visual spatial memory (one of the subtests of the nonverbal IQ test) was the main predictor of variance in the language scores of the children using cochlear implants.

A clinical report on speech production of cochlear implant users

OBJECTIVE

The aim was to assess articulation and speech intelligibility over time in a group of cochlear implant users implanted at 8 yr or over. The hypothesis was that the postoperative speech production performance would be greater than the preoperative performance.

DESIGN

A test of intelligibility using sentences and an articulation test measuring non-imitative elicited speech were administered to 11 and 10 subjects, respectively, who were implanted with the 22-electrode cochlear implant. Nine subjects received both tests. Age at implantation ranged from 8 yr to 20 yr and implant use ranged from 1 yr to 4 yr 5 mo.

RESULTS

For both the intelligibility and articulation tests roughly half of the subjects showed significant improvements over time and group mean postoperative performance significantly exceeded preoperative performance. Improvements occurred for front, middle, and back consonants; for stops, fricatives, and glides and for voiceless and voiced consonants.

CONCLUSIONS

Despite being deprived of acoustic speech information for many childhood years, roughly half of the patients assessed showed significant gains in speech intelligibility and articulation postimplantation. The lack of a control group of non-implanted patients means that we cannot separate out the influence of the implant on speech production from other influences such as training and tactile-kinaesthetic feedback.

Electrode position, repetition rate, and speech perception by early- and late-deafened cochlear implant patients

Psychophysical and speech perception studies were conducted on eight patients using the 22-electrode cochlear implant manufactured by Cochlear Pty. Ltd. Four early-deafened patients became deafened at 1-3 years of age and were implanted at 5-14 years of age. Four late-deafened (postlingual adult) patients became deafened at 38-47 years of age and were implanted at 42-68 years of age. Psychophysical studies measured the discrimination of trajectories with time-varying electrode positions and repetition rates. Speech perception studies measured performance using two speech coding strategies: a multi-electrode strategy which coded the first and second formant frequencies, the amplitudes of the two formants, and the fundamental frequency; and a single-electrode strategy which coded the amplitudes of the first and second formants, and the fundamental frequency. In general, the four late-deafened patients and one early-deafened patient were more successful than the other three early-deafened patients in the discrimination of electrode position trajectories and in speech perception using the multi-electrode strategy. Three of the four late-deafened patients were more successful than the early-deafened patients in the discrimination of repetition rate trajectories. Speech perception performance in the single-electrode strategy was closely related to performance in repetition rate discrimination. The improvement in speech perception performance from the single-electrode to multi-electrode strategy was consistent with successful performance in electrode discrimination.

A multiple-electrode intracochlear implant for children

A multiple-electrode intracochlear implant that provides 21 stimulus channels has been designed for use in young children. It is smaller than the adult version and has magnets to facilitate the attachment of the headset. It has been implanted in two children aged 5 and 10 years. The two children both lost hearing in their third year, when they were still learning language. Following implantation, it was possible to determine threshold and comfortable listening levels for each electrode pair. This was facilitated in the younger child by prior training in scaling visual and electrotactile stimuli. Both children are regular users of the implant, and a training and assessment program has been commenced.

Cognitive processing in children using cochlear implants: the relationship between visual memory, attention, and executive functions and developing language skills

We performed this study to determine whether children using a cochlear implant performed differently from age- and gender-matched hearing aid users on 8 neuropsychological measures of visual memory, attention, and executive functioning. The study also examined whether differences in cognitive skills could account for some of the observed variance in speech perception, vocabulary, and language abilities of hearing-impaired children. In contrast to previous studies, our results revealed no significant cognitive differences between children who use a cochlear implant and children who use hearing aids. Partial correlation analysis indicated that the children's visual memory skills, ie, their recognition memory, delayed recall, and paired associative learning memory skills, correlated significantly with their language skills. When examined at a significance level of .01, attention and executive functioning skills did not relate to the children's developing speech perception, vocabulary, or language skills. The results suggested that differences in visual memory skills may account for some of the variance seen in the language abilities of children using implants and children using hearing aids.

Electrode discrimination by early-deafened subjects using the cochlear limited multiple-electrode cochlear implant

OBJECTIVE

The aims of this study were to determine whether electrode discrimination by early-deafened subjects using the Cochlear Limited prosthesis varied at different locations on the electrode array, was influenced by the effects of auditory deprivation and experience with electric stimulation, and was related to speech perception.

DESIGN

Difference limens for electrode discrimination were measured in 16 early-deafened subjects at three positions on the array: electrodes 18 (apical), 14 (mid), and 8 (basal). Electrodes were stimulated using random variations in current level to minimize the influence of loudness cues. Assessed were correlations between the difference limens, subject variables related to auditory deprivation (age at onset of deafness, duration of deafness, and age at implantation) and auditory experience (duration of implant use and the total time period of auditory experience), and speech perception scores from two closed-set and two open-set tests.

RESULTS

The average difference limens across the three positions were less than two electrodes for 75% of subjects, with average limens between 2 and 6.5 electrodes for the remaining 25% of subjects. Significant differences across the three positions were found for 69% of subjects. The average limens and those at the basal position positively correlated with variables related to auditory deprivation, with larger limens for subjects implanted at a later age and with a longer duration of deafness. The average limens and those at the apical position negatively correlated with closed-set speech perception scores, with lower scores for subjects with larger limens, but not with open-set scores. Speech scores also negatively correlated with variables related to auditory deprivation.

CONCLUSIONS

These findings showed that early-deafened subjects were generally successful in electrode discrimination although performance varied across the array for over half the subjects. Discrimination performance was influenced by the effects of auditory deprivation, and both electrode discrimination and variables related to auditory deprivation influenced closed-set speech perception.

The results in patients implanted with the nucleus double array cochlear implant: pitch discrimination and auditory performance

OBJECTIVE

In patients with total or surgically inaccessible cochlear obliteration, only a reduced number of active electrodes can be inserted with standard cochlear implants, resulting in below average auditory performance. Therefore, a special implant with two electrode arrays was developed on the basis of the Nucleus 22 cochlear implant, the socalled Double Array. One electrode array with 11 active electrodes is inserted into the basal turn of the cochlea, while the second array with 10 active electrodes is inserted into the second turn. The Double Array is now available on the basis of the more advanced Nucleus 24 with 11 active electrodes on each array and two reference electrodes, one at the case and the second one an additional ball electrode, which is placed under the temporalis muscle. For device description and surgical technique see Lenarz et al. (2001). This paper presents psychophysical data on pitch discrimination and auditory performance of patients implanted with a Double Array on the basis of the Nucleus 22.

STUDY DESIGN

A prospective intra-individual study using a Latin square paradigm was performed in six adult patients with obliterated cochlea who received the Nucleus 22 Double Array. After appropriate fitting and loudness balancing, patients were tested either with the basal, the apical or both electrode arrays. Apart from auditory performance tests including numbers and monosyllable word tests, pitch discrimination was determined with a defined procedure.

RESULTS

When activating each array alone, auditory performance was better with the basal array than with the apical array. Both arrays together showed marked improvement compared with the basal array, indicating an additional effect of the second array. Pitch discrimination was significantly better for the electrodes in the basal turn than in the second turn, indicating differences in electrical excitation of the auditory nerve fibers. Pitch discrimination was positively correlated with auditory performance data.

CONCLUSION

The additional apical array leads to significant improvement in auditory performance in patients with obliterated cochleae by increasing the number of intracochlear electrodes. Despite reduced pitch discrimination, the apical array provides important information for speech recognition. For this reason the Double Array provides a profound advantage for patients with obliterated or surgically inaccessible cochleae.

Results of speech perception and speech production training for three prelingually deaf patients using a multiple-electrode cochlear implant

Five studies were conducted to measure changes in the perception and production of selected speech targets, with training, in three prelingually deaf patients. The two adults and one adolescent were implanted with the Cochlear (Nucleus) multiple-electrode prosthesis. The studies were perception and production of nasal consonants; perception of syllable-final consonants; perception and production of alveolar consonants; auditory-visual perception of alveolar consonants; and perception and production of vowels. Perceptual data were collected in the audition (implant)-alone condition, except for the auditory-visual perception of alveolar consonants where the audition-alone, vision-alone, and auditory-visual conditions were used. Speech perception data in the audition-alone condition were also collected from four postlingually deaf adult implant patients, without training, to indicate differences between the two classes of patients. The three prelingually deaf patients generally showed some improvements in speech production. In perception, improvements were recorded only for individual patients in some studies. The performance of the adolescent was better than that of the two adults in all cases. The perceptual performance of the postlingually deaf patients was superior to that of the prelingually deaf patients in all cases.

A multiple-channel cochlear implant. An evaluation using an open-set word test

Multiple-channel electrical stimulation of the hearing nerve in conjunction with speechreading has helped two post-lingually deaf patients with total hearing losses understand running speech in every day situations. This has been confirmed using open-set phonetically balanced word tests, where the patients achieved 60% and 40% scores with isolated-words, and 80% and 73% for phonemes-in-isolated words. The tests also showed that the cochlear implant improved word recognition by a factor of four in one patient and two in another, compared with speechreading alone. The speech processor used, extracted the voicing frequency and energy, and the frequency and energy of the dominant spectral peak in the mid-frequency range. The parameters for voicing determined the rate of stimulation for all electrodes, and the parameters for the dominant spectral peak in the mid-frequency range determined the site of electrode stimulation and current level.

Psychophysical studies using a multiple-electrode cochlear implant in patients who were deafened early in life

Psychophysical studies were conducted on 10 cochlear implant patients, between 5 and 23 years of age at the time of surgery, who were deafened prior to 4 years of age. The multiple-electrode prosthesis manufactured by Cochlear Ltd. was used. Identification studies, the recognition of 2-4 stimuli after some training, were conducted on 3 of the 10 patients. For current level and repetition rate identification, performance was comparable to that observed for postlingual adult patients. For electrode position identification, however, performance was much poorer than that observed for postlingual adults. In general, the difference limens for current level, repetition rate and duration, and the gap detection thresholds were similar to those observed for postlingual adults. For 3 patients whose etiology was Usher's syndrome, the repetition rate limens at higher rates were larger than those of the other patients. The limens for electrode position, measured in a discrimination task, were 1-3 electrodes for most patients. However, for 3 patients, limens of 6-10 electrodes were recorded. For numerosity judgements, the counting of stimuli in a temporal series as a function of the rate of presentation, the patients were less successful at counting for rates of 3-8/s than for lower rates (1-2/s).

Timolol kinetics in chronic renal insufficiency

A single-dose kinetic study of oral timolol, 20 mg, was undertaken in 3 groups of volunteers with varying degrees of renal function--(1) 10 normal subjects (N); (2) 9 patients with moderate chronic renal insufficiency (MCRI; C cr, 20 to 50 ml/min); (3) 4 patients with end-stage renal disease (ESRD)--to assess the need for dosage modification as renal function diminishes. There were borderline statistical differences in absorption between groups. The mean peak concentration (C max) was 84.3 +/- 44.8 ng/ml at 0.8 +/- 0.4 hr for N and 87.1 +/- 22.8 ng/ml at 1.7 +/- 1.2 hr (p, NS) for MCRI. N and MCRI mean half-lives (5.2 +/- 2.6 hr and 4.0 +/- 1.2 hr) were not statistically different. Salivary levels correlated with plasma levels in 3 N and 1 MCRI patient. Group differences in blood pressure and pulse response to timolol seems to reflect differences present at baseline with percent change from baseline identical for the two groups except at 12 to 24 hr. Administration of timolol on an interdialysis day revealed similar kinetic and physiologic response in the normal and the MCRI group. During dialysis, timolol, 20 mg, induced significant hypotension and bradycardia.

Dual electrode stimulation using the nucleus CI24RE cochlear implant: electrode impedance and pitch ranking studies

OBJECTIVE

The first aim of the study was to determine the reduction in electrode impedances using dual electrode stimulation compared with single electrode stimulation in the new Nucleus CI24RE receiver-stimulator. The CI24RE is connected to the Nucleus 22-electrode intracochlear array. Dual electrode stimulation is produced by electrically coupling two adjacent single electrodes. The second aim was to determine whether dual electrode stimulation produced pitch percepts that were intermediate to the pitch of the two adjacent single electrodes.

DESIGN

Eight postlingually hearing-impaired adults with severe to profound loss, implanted with the CI24RE, participated in the study. Electrode impedances were measured by using the standard telemetry function of the system. A pitch ranking task was used to measure pitch for dual and single electrodes. Seven sets of three electrodes along the electrode array were tested. Each set of electrodes consisted of a dual electrode and the two adjacent single electrodes. Pitch ranking was measured using a two-alternative forced choice procedure, with the three electrodes in each set paired with each other as AB and BA pairs. The subject indicated which of the two stimuli had the higher pitch. Random variation in current level was used to remove any loudness cues.

RESULTS

The average electrode impedance was 38.6% lower for dual electrodes compared with single electrodes. Three subjects were able to successfully rank the three electrodes in each set in the expected tonotopic order for all seven sets of electrodes along the array. Three other subjects were able to rank sets of electrodes in the tonotopic order for most of the tested positions on the array. The remaining two subjects gave more variable pitch ranking across positions along the array, although successful tonotopic ranking was demonstrated for several sets of electrodes.

CONCLUSIONS

Dual electrode stimulation with the CI24RE receiver-stimulator produced systematically lower electrode impedances and was capable of producing pitch percepts that were intermediate to those produced by the corresponding adjacent single electrodes. This makes available up to 43 channels of stimulation from 22 single electrodes.

Cochlear implant place psychophysics 1. Pitch estimation with deeply inserted electrodes

Numerical estimation of pitch was performed by 8 adult subjects implanted with cochlear prostheses manufactured by Cochlear Limited. The electrode arrays had been inserted into the scale tympani to between one and one and a half turns of the cochlea. Using bipolar stimulation, the pitch estimates for each subjects showed an overall reduction with insertion depth of the stimulated electrode. However, for several subjects, after decreasing regularly for the more basal electrodes, pitch estimates showed an abrupt decrease, followed in some cases by a region of low pitch. Two of the subjects, implanted with a modified electrode array, the '20 + 2' which allowed monopolar in addition to bipolar stimulation, exhibited an abrupt decrease in pitch estimate with bipolar but not with monopolar stimulation. In these two subjects, for stimulating electrodes inserted more deeply than about three quarters of a turn, bipolar stimuli produced lower pitch sensations, and presumably more apical neural excitation patterns, than monopolar stimuli.

Cochlear implant place psychophysics. 2. Comparison of forward masking and pitch estimation data

Results for forward masking and numerical estimation of pitch were compared in a group of 6 adult subjects implanted with cochlear prostheses manufactured by Cochlear Limited. Data were collected for bipolar + 1 stimulation in all subjects, and for stimulation in one other mode, either common ground or monopolar, for all subjects but one. The pitch data show various irregularities and in each case can be seen to be broadly consistent with the corresponding forward masking data. It is shown that a 'centre of gravity' of the forward masking distribution varies with masker electrode in a manner that is qualitatively very similar to the variation of pitch estimate. It is suggested that, while pitch estimation results are consistent with those from forward masking, the latter contain more detailed information that may be useful in understanding intersubject variations in speech comprehension.

Formant frequency values of vowels produced by preadolescent boys and girls

The fundamental frequency (F0) and the first three formant frequency (F1, F2, and F3) values of vowels produced by 40 preadolescents were measured. There were five boys and five girls in each of four age groups: 5, 7, 9, and 11 years old. The 11 nondiphthong vowels of Australian English which can be produced in a stressed syllable were used. The F0 values decreased with increases in age, but there was no difference between boys and girls. In general, the F1, F2, and F3 values decreased with increases in age, and the values for girls were higher than those for boys.

Electrode discrimination and speech perception in young children using cochlear implants

OBJECTIVE

The aim was to determine the efficacy of a child-appropriate procedure to assess electrode discrimination ability in young children using cochlear implants and to investigate the relationship of electrode discrimination ability and speech perception performance in children implanted at a young age.

DESIGN

An adaptation of the play audiometry procedure was used to assess electrode discrimination in seventeen 4- to 10-yr-old children. The children were required to respond with a game-like motor response when a repeating stimulation on a reference electrode "changed" to a different electrode. They were also assessed on a speech feature discrimination test, a closed-set word recognition test and a nonverbal intelligence task.

RESULTS

Sixty-five percent of subjects demonstrated ability to discriminate adjacent electrodes in mid and apical regions of the cochlea, whilst the remaining subjects needed electrode separations of between two and nine electrodes for successful discrimination. In a forward stepwise regression analysis electrode discrimination ability was found to be the strongest factor in accounting for variance in the speech perception scores. Subject variables such as duration of deafness, nonverbal intelligence and implant experience did not significantly account for further variance in the speech perception scores for this group of children.

CONCLUSIONS

Electrode discrimination ability was the strongest factor in predicting performance on speech perception measures in a group of children using cochlear implants.