Patterns of variability and gene flow in Medicago citrina, an endangered endemic of islands in the western Mediterranean, as revealed by amplified fragment length polymorphism (AFLP).

Medicago citrina is an endangered western Mediterranean endemic that grows only on small islets of the Balearic archipelago and off the eastern Spanish coast. Only 10 isolated subpopulations are currently known (four from Ibiza, three from Cabrera, two from Columbretes and one from an offshore islet in northern Alicante province), constituting a severely fragmented genetic system. Data were analysed with the unweighted pair-group method using arithmetic averages (UPGMA) and principle coordinates analysis (PCOA), revealing several distinct groups. Genetic diversity indices indicated that Ibizan subpopulations had the highest genetic variability (Nei's index: 0.1463; Shannon's index: 0.228), whereas the lowest variability was found in Alicante (Nei's index: 0.035; Shannon's index: 0.050) and Cabrera (Nei's index: 0.068; Shannon's index: 0.104). These latter populations show the highest FST values (FST = 0.548) revealing high differentiation between them. Columbretes subpopulations formed a defined single group, although it also included some Ibizan samples. The smallest FST values, obtained between Ibiza and Columbretes (FST = 0.185), are not correlated with geographical proximity, but appear to be related to the geologically recent volcanic origin of the Columbretes islands (300,000 years ago). According to the distribution of the Ibizan samples in the dendrogram and the FST values, the best hypothesis is to regard the Ibizan subpopulations as the centre of genetic diversity of the currently known subpopulations. Our results suggest migratory scenarios from Ibiza to Columbretes based mainly on zoochory probably by seabirds. Finally, recommendations are provided for management strategies to facilitate the conservation of this endangered species.

A study of intra-cochlear electrodes and tissue interface by electrochemical impedance methods in vivo.

This paper presents methods, results and analysis for measurements of the electrochemical impedance of platinum electrodes (approximately 0.43 mm2) over a 6-month implantation in the cat cochlea. The study aimed to improve our understanding of the effects of tissue response on impedance behaviour. An increase in impedance in the post-operative period was evident with a rise of the distorted arc at high frequencies in the complex plane, correlating to anomalous charge transport at the electrode-tissue interface. The impedance at low frequencies generally showed a capacitive dispersion modelled as a constant phase element, indicating a blocking characteristic of the electrodes. The study suggests that a reduction and changes in composition of perilymph or extracellular fluid adjacent to the electrodes, as a consequence of tissue response, causes the elevated "contact impedance". This affects the efficiency and quality of neural stimulating electrodes and neural recording electrodes. The finding of the crucial role of perilymph or extracellular fluid thin layer provides a new strategy for surface materials of neural electrodes, which is discussed in the paper. The interface characteristics must be considered during interpretation of studies undertaken in vitro or in acute experiments in vivo, where physiological fluid is abundant.

Conversion from the SPEAK to the ACE strategy in children using the nucleus 24 cochlear implant system: speech perception and speech production outcomes.

OBJECTIVE: The main objective of this study was to assess whether speech perception and speech production in children using the Nucleus 24 cochlear implant system improved with a change in speech processing strategy from the SPEAK to the Advanced Combination Encoder (ACE) strategy. The major difference between the two strategies is that ACE uses a higher stimulation rate (in this study the stimulation rate was 900 Hz per channel) compared with the SPEAK strategy, where the stimulation rate is 250 Hz per channel. Information also was obtained regarding the adjustment period after conversion to the ACE strategy. DESIGN: An ABA experimental design was used where scores were initially obtained using the SPEAK strategy' (in the initial A time interval), and subsequently performance was assessed using the ACE strategy (B time interval) and then again with the SPEAK strategy (second A time interval). The duration of the B interval was 10 wk, and the duration for the second A interval was 4 wk. Seven children aged between 9 and 16 yr who had at least 6 mo experience with the SPEAK strategy participated. Open-set monosyllabic CNC word perception in quiet and Speech Intelligibility Test sentence perception in noise was evaluated at the end of each of the time intervals. Word perception was also monitored at fortnightly intervals during the B time interval. Speech production was assessed at the end of the initial A time interval and at the end of the B time interval. RESULTS: Mean word and phoneme scores for open-set words in quiet for the group of seven children were significantly higher with the ACE strategy as compared with the SPEAK strategy scores obtained in both of the A time intervals. For sentences in noise, mean scores using the ACE strategy as well as the SPEAK strategy at the second A evaluation point were significantly higher than the scores using the SPEAK strategy measured at the first A time interval. This suggests that learning effects may have influenced outcomes. For some subjects, an initial decrease in scores was found during the initial 2-wk period after fitting the ACE strategy; however, scores subsequently were found to be similar to or higher than those when using the initial SPEAK strategy. Analysis of speech production assessments showed an improvement in the medial consonant scores after using the ACE strategy. CONCLUSIONS: This study demonstrated that some children were able to benefit from the additional information provided by the ACE strategy as compared with the SPEAK strategy. However, the differences in overall performance between the two strategies appear to be relatively small.

The role of radiographic phase-contrast imaging in the development of intracochlear electrode arrays.

OBJECTIVE: This study describes the application of a new radiographic imaging modality, phase-contrast radiography, to in vitro human temporal bone imaging and investigates its use in the development of new electrode arrays for cochlear implants. BACKGROUND: The development of perimodiolar electrode arrays for cochlear implants requires detailed information from postoperative radiologic assessment on the position of the array in relation to the cochlear structures. Current standard radiographic techniques provide only limited details. MATERIALS AND METHODS: Nucleus standard electrode arrays and perimodiolar Contour electrode arrays were implanted into the scala tympani of 11 human temporal bones. Both conventional and phase-contrast radiographs were taken of each temporal bone for comparative purposes. RESULTS: Phase-contrast imaging provides better visualization of anatomic details of the inner ear and of the structure of the intracochlear electrode array, and better definition of electrode location in relation to cochlear walls. CONCLUSION: Phase-contrast radiography offers significant improvement over conventional radiography in images of in vitro human temporal bones. It seems to be a valuable tool in the development of intracochlear electrode arrays and cochlear implant research. However, this new radiographic technique still requires certain computational and physics challenges to be addressed before its clinical use can be established.

Chronic electrical stimulation of the auditory nerve using high surface area (HiQ) platinum electrodes.

High surface area cochlear implant electrodes with much smaller geometric surface areas than current designs might be used in the future to increase the number of stimulating electrodes along the carrier. Potential problems with an increase in charge density for a common stimulus resulting from decreasing the geometric surface area would be reduced by the enlarged real surface area of such electrodes. Electrochemically modified (HiQ) platinum (Pt) electrodes, with a real surface area approximately 75 times greater than the current standard Pt electrodes of the same geometric size, had shown in vitro a low polarization (Z(pol)) and electrode impedance (Z(e)), as well as a low residual direct current (DC). In this study we examined the chronic performance of HiQ electrodes in cats, which were bilaterally implanted with a two-channel HiQ or standard Pt scala tympani electrode array and unilaterally stimulated for periods of up to 2390 h. Stimuli consisted of 50 micros/phase charge-balanced biphasic current pulses presented at 2000 pulses/s/channel with a 50% duty cycle. Electrode impedance (Z(e)), access resistance (R(a)) and polarization impedance (Z(pol)) were calculated from current and voltage measurements obtained periodically throughout the implantation period. Immediately following implantation HiQ electrodes showed a significantly smaller Z(pol), resulting in a reduced Z(e) (P<0.0001) compared to standard electrodes, while there was no significant difference between R(a) of both electrode designs (P=0.91). Subsequently, Z(e) generally increased mainly due to a rise in R(a), which dominated Z(e) and obliterated the effect of a lower Z(pol) on Z(e) in HiQ electrodes. Peak R(a) levels correlated closely (r=0.85) with the amount of intracochlear fibrous tissue found adjacent to the array. Following explantation of the array, voltage waveforms for both electrode designs recorded in saline were again very similar to those recorded immediately after implantation. Mean DC levels were consistently lower for HiQ electrodes compared with standard electrodes (22.45 nA vs 134.7 nA). Histopathological examination of corresponding cochlear sections comparing the stimulated test side with the unstimulated control side showed no significant difference (P>0.05) for either animals implanted with HiQ electrodes (n=6) or standard electrodes (n=2). Nor were there any significant differences between the spiral ganglion cell density of the basal turn implanted with HiQ or standard electrodes for both the stimulated test (P=0.31) and the unstimulated control side (P=0.84). Although these findings are based on a small group of animals implanted with standard electrodes (n=2), and those negative statistical results could potentially be due to the small sample size, similar spiral ganglion cell survival was found in a previous study of a larger group of animals using standard electrodes stimulated with the same stimulus paradigm as in the present study [Xu et al. (1997) Hear. Res. 105, 1-29]. Our data indicate that while some initial advantages of HiQ electrodes are lost during chronic implantation due to intracochlear fibrous tissue growth, low DC levels and the high surface area appear to be maintained, suggesting that HiQ electrodes may have important clinical applications.

The contour electrode array: safety study and initial patient trials of a new perimodiolar design.

OBJECTIVE: The aim of these studies was to investigate the insertion properties and safety of a new intracochlear perimodiolar electrode array design (Contour). BACKGROUND: An electrode array positioned close to the neural elements could be expected to reduce stimulation thresholds and might potentially reduce channel interaction. METHODS: Two sequential studies were conducted. In study 1, the Contour electrode array was inserted in 12 human temporal bones. After cochlear surface preparation, the position of the array was noted and the basilar membrane was examined for insertion damage. On the basis of the outcome of this temporal bone study, study 2 investigated the Contour array, mounted on a Nucleus CI-24 M device and implanted in three adult patients. RESULTS: Study I showed that in 10 temporal bones, the Contour array was positioned close to the modiolus, and the basilar membrane was intact. In the two remaining bones, the arrays had pierced the basilar membrane and were positioned in the scala vestibuli apical to the penetration. Statistical analysis showed an equivalent probability of insertion-induced damage of the two array designs. In study 2, image analysis indicated that the Contour electrodes were positioned closer to the modiolus than the standard Nucleus straight array. Lower T and C levels, but higher impedance values, were recorded from electrodes close to the modiolus. Initial speech perception data showed that all patients gained useful open-set speech perception, two patients achieving scores of 100% on sentence material 3 months postoperatively. CONCLUSIONS: The temporal bone studies showed the Contour electrode array to be generally positioned closer to the modiolus than the standard Nucleus straight array, and to have an equivalent probability of causing insertion-induced damage.

Comparison of electrode position in the human cochlea using various perimodiolar electrode arrays.

OBJECTIVE: This study was conducted to evaluate the insertion properties and intracochlear trajectories of three perimodiolar electrode array designs and to compare these designs with the standard Cochlear/Melbourne array. BACKGROUND: Advantages to be expected of a perimodiolar electrode array include both a reduction in stimulus thresholds and an increase in dynamic range, resulting in a more localized stimulation pattern of the spiral ganglion cells, reduced power consumption, and, therefore, longer speech processor battery life. METHODS: The test arrays were implanted into human temporal bones. Image analysis was performed on a radiograph taken after the insertion. The cochleas were then histologically processed with the electrode array in situ, and the resulting sections were subsequently assessed for position of the electrode array as well as insertion-related intracochlear damage. RESULTS: All perimodiolar electrode arrays were inserted deeper and showed trajectories that were generally closer to the modiolus compared with the standard electrode array. However, although the precurved array designs did not show significant insertion trauma, the method of insertion needed improvement. After insertion of the straight electrode array with positioner, signs of severe insertion trauma in the majority of implanted cochleas were found. CONCLUSIONS: Although it was possible to position the electrode arrays close to the modiolus, none of the three perimodiolar designs investigated fulfilled satisfactorily all three criteria of being easy, safe, and atraumatic to implant.

Generalization of tactile perceptual skills to new context following tactile-alone word recognition training with the Tickle Talker.

The Tickle Talker is an electrotactile speech perception device. Subjects were evaluated using the device in various tactile-alone and tactile-visual contexts to assess the generalization to other contexts of tactile-alone perceptual skills. The subjects were from a group of six normally hearing subjects who had previously received 12 to 33 h of tactile-alone word recognition training and had learned an average vocabulary of 50 words [Galvin et al., J. Acoust. Soc. Am. 106, 1084-1089 (1999)]. The tactile-alone evaluation contexts were sentences, unfamiliar talkers, and untrained words. The tactile-visual evaluation contexts were closed-set words, open-set words, and open-set sentences. Tactile-alone perceptual skills were generalized to unfamiliar speakers, sentences, and untrained words, though scores indicated that generalization was not complete. In contrast, the generalization of skills to tactile-visual contexts was minimal or absent. The potential value of tactile-alone training for hearing-impaired users of the Tickle Talker is discussed.

A comparison of Tactaid II+ and Tactaid 7 use by adults with a profound hearing impairment.

OBJECTIVE: To evaluate and compare use of the Tactaid II+ and the Tactaid 7, in terms of speech perception, by adults with a hearing impairment. DESIGN: Eight adults used one device daily for approximately 10 wk and attended seven training sessions. Performance was measured with tests of phonetic contrast perception, closed-set vowel and consonant identification, word and phoneme recognition in monosyllabic word lists, word recognition in sentences and speechtracking rate. A questionnaire was also administered. The protocol was repeated with the alternative device. RESULTS: With each device, the group discriminated most phonetic contrasts at better-than-chance levels and demonstrated somewhat enhanced visual or auditory-visual perception when measured in terms of vowel identification, monosyllabic word recognition and speechtracking rate. An increase in speechtracking rate was also demonstrated for some individuals. Subjects generally reported little subjective improvement in speech perception and production, but were satisfied with the physical attributes of each device. Five of six subjects preferred the Tactaid 7. CONCLUSIONS: The Tactaid II+ and the Tactaid 7 provided suprasegmental and segmental information, enabling the group to discriminate phonetic contrasts and improve their perception of some speech materials. No consistent advantage was found for either device, thought most subjects preferred the Tactaid 7. Alternatives likely to provide a greater benefit to communication should be considered before a Tactaid fitting.

Acquisition of a tactile-alone vocabulary by normally hearing users of the Tickle Talker.

Tactile-alone word recognition training was provided to six normally hearing users of the Tickle Talker, an electrotactile speech perception device. A mean group tactile-alone vocabulary of 31 words was learned in 12 h of training. These results were comparable to, or superior to, those reported for other tactile devices and Tadoma. With increased training the group became faster at learning tactually new words, which were introduced in small training sets. However, as their tactile-alone vocabulary grew, subjects required more training time to reach the pass criterion when evaluated on their recognition of their whole vocabulary list. A maximum possible vocabulary size was not established. The application of tactile-alone training with hearing-impaired users of the device is discussed.

A modification of play audiometry to assess speech discrimination ability in severe-profoundly deaf 2- to 4-year-old children.

OBJECTIVE: The aim was to develop an assessment procedure that was independent of language and speech production ability, to test speech feature discrimination in severe-profoundly deaf children 2 to 4 yr of age. DESIGN: The procedure being trialed was adapted from existing procedures. The child was required to respond with a game-like motor response to a "change" in a speech stimulus that was being presented repeatedly through a speaker. The change occurred at randomly determined times, and false alarm responses were measured during the waiting periods (while the child waited for the change). Two- to four-yr-old normally hearing children and hearing-impaired children using hearing aids and a group of 4-yr-old hearing-impaired children using cochlear implants were assessed on the task. RESULTS: More than 82% of the 3- and 4-yr-old normally hearing and hearing-impaired children were able to complete the testing for the eight speech sound contrasts within three 20 minute sessions. Fifty percent of the 2-yr-old normally hearing and hearing-impaired children were able to condition and complete the task. All of the normally hearing children who completed the task successfully discriminated all speech sound contrasts. The performance of the hearing-impaired children using hearing aids was influenced by the degree of hearing loss and the type of speech contrast being tested. Similarly, the average performance of the children using cochlear implants was better for easier contrasts such as /ba/bi/ with contrasting vowel formant cues. CONCLUSIONS: This procedure has potential for use as a reliable clinical and research tool for assessing the development of auditory discrimination ability in 2- to 4-yr-old severe-profoundly deaf children.

Speech perception results for children with implants with different levels of preoperative residual hearing.

OBJECTIVE: Many reports have established that hearing-impaired children using the Nucleus 22-channel cochlear implant may show both significant benefits to lipreading and significant scores on open-set words and sentences using electrical stimulation only. These findings have raised questions about whether severely or severely-to-profoundly deaf children should be candidates for cochlear implants. To study this question, postoperative results for implanted children with different levels of preoperative residual hearing were evaluated in terms of speech perception benefits. STUDY DESIGN/SETTING: A retrospective study of the first 117 children, sequentially, to undergo implantation in the Melbourne and Sydney Cochlear Implant Clinics was undertaken. All children had been assessed by and received their implants in a tertiary referral centre. MAIN OUTCOME MEASURES: To assess aided residual hearing, the children were grouped into four categories of hearing on the basis of their aided residual hearing thresholds measured preoperatively. To assess benefits, the scores of children on standard speech perception tests were reviewed. As different tests were used for children with different ages and language skills, children were grouped into categories according to the level of postoperative speech perception benefit. RESULTS: The results showed that children in the higher categories of aided preoperative residual hearing showed significant scores on open-set word and sentence perception tests using the implant alone. For children in lower categories of aided residual hearing, results were variable within the groups. More than 90% of children with implants with aided residual hearing thresholds in the speech range above 1 kHz achieved open-set understanding of words and sentences. CONCLUSION: While the results of this preliminary study confirm previous findings of differential outcomes for children with different levels of preoperative residual hearing, they suggest that children with severe to profound hearing impairments should be considered for cochlear implantation.

The effect of language knowledge on speech perception: what are we really assessing?

OBJECTIVE: The authors examined whether open-set speech perception scores are limited by knowledge of vocabulary and syntax and further considered whether remediation of vocabulary and syntax will increase open-set speech perception scores. STUDY DESIGN: This was a repeated-measures study design in the setting of a primary (elementary) school for the hearing-impaired. PATIENTS: The study population was composed of three hearing-impaired children using Nucleus 22-channel cochlear implant. INTERVENTION: Intervention used was language remediation sessions. MAIN OUTCOME MEASURES: The main outcome measures were assessment of auditory-alone speech perception benefit using open-set words and sentences and assessment of syntactic knowledge using the Test of Syntactic Ability. Outcome measures were applied before and after remediation. RESULTS: Child 1 and child 2 showed a significant postremediation improvement in their overall scores on the Test of Syntactic Ability and in their ability to perceive words learned during remediation. Child 1 and child 2 also showed a significant improvement in their scores on a modified Bamford-Kowal-Bench open-set sentence test, which specifically targeted grammatical constructs trained in remediation sessions. CONCLUSIONS: Remediation of language knowledge deficits significantly improved open-set speech perception for two children, suggesting a need to include language remediation in cochlear implant habilitation programs.

Speech perception in children using the advanced Speak speech-processing strategy.

The Speak speech-processing strategy, developed by the University of Melbourne and commercialized by Cochlear Pty Limited for use in the new Spectra 22 speech processor, has been shown to provide improved speech perception for adults in both quiet and noisy situations. The present study evaluated the ability of children experienced in the use of the Multipeak (Mpeak) speech-processing strategy (implemented in the Nucleus Minisystem-22 cochlear implant) to adapt to and benefit from the advanced Speak speech-processing strategy (implemented in the Nucleus Spectra 22 speech processor). Twelve children were assessed using Mpeak and Speak over a period of 8 months. All of the children had over 1 year's previous experience with Mpeak, and all were able to score significantly on open-set word and sentence tests using the cochlear implant alone. Children were assessed with both live-voice and recorded speech materials, including Consonant-Nucleus-Consonant monosyllabic words and Speech Intelligibility Test sentences. Assessments were made in both quiet and in noise. Assessments were made at 3-week intervals to investigate the ability of the children to adapt to the new speech-processing strategy. For most of the children, a significant advantage was evident when using the Speak strategy as compared with Mpeak. For 4 of the children, there was no decrement in speech perception scores immediately following fitting with Speak. Eight of the children showed a small (10% to 20%) decrement in speech perception scores for between 3 and 6 weeks following the changeover to Speak. After 24 weeks' experience with Speak, 11 of the children had shown a steady increase in speech perception scores, with final Speak scores higher than for Mpeak. Only 1 child showed a significant decrement in speech perception with Speak, which did not recover to original Mpeak levels.

Improved electrotactile speech processor: Tickle Talker.

The Tickle Talker, an eight-channel electrotactile speech processor, has been developed from continuing research at the University of Melbourne. The development of the device has focused on production of reliable speech-processing hardware, design of cosmetically and ergonometrically acceptable electrode transducers, implementation of acute and chronic biomedical studies demonstrating device safety, design and testing of alternative speech-encoding strategies to provide benefit to speech perception and production, and design and testing of appropriate training methods for optimizing benefits. The Tickle Talker has been shown to provide benefits in supplementing lipreading or aided residual hearing for hearing-impaired adults and children. Improvements in speech processing have resulted in an increase in benefits to speech perception, and open the way for more flexible approaches to encoding speech input. Continuing development of the electrode circuitry has now produced a device that is robust and has an extended battery life. Safety studies have clearly demonstrated that there are no long-term contraindications to device use. The results suggest that the device has a role to play in rehabilitation programs for severely and profoundly hearing-impaired adults and children.

Articulation accuracy of children using an electrotactile speech processor.

OBJECTIVE: Use of wearable tactile speech perception devices is suggested to help overcome the difficulties in speech production resulting from severe and profound hearing impairment in children. This suggestion is based on the assumption that subjects can use tactile input in isolation, or in combination with information from residual aided hearing, to monitor and modify their speech. The present study evaluated the benefits to articulation provided through use of a multichannel electrotactile device ("Tickle Talker"). DESIGN: Six profoundly hearing-impaired children were videotaped speaking with the Tickle Talker on and with the Tickle Talker off during conversations with their audiologist. Five of the subjects also wore their binaural hearing aids during all recorded conversations. The number of vowels, consonants, and overall phonemes correctly articulated by each child in the two conditions were compared. RESULTS: One subject improved articulation of initial consonants and initial phonemes; one subject improved articulation of total vowels, total consonants, initial consonants, total phonemes, and initial phonemes; and a third subject improved articulation of total vowels and medial phonemes. CONCLUSIONS: Use of on-line tactile feedback from the Tickle Talker may benefit the articulation accuracy of some children, and the device may therefore be suitable to use with children who have not responded to more traditional speech training techniques.