Chronic depolarization enhances the trophic effects of brain-derived neurotrophic factor in rescuing auditory neurons following a sensorineural hearing loss.
(73/786)
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. (+info)
Influence of voice similarity on talker discrimination in children with normal hearing and children with cochlear implants.
(74/786)
The perception of voice similarity was examined in 5-year-old children with normal hearing sensitivity and in pediatric cochlear implant users, 5-12 years of age. Recorded sentences were manipulated to form a continuum of similar-sounding voices. An adaptive procedure was then used to determine how acoustically different, in terms of average fundamental and formant frequencies, 2 sentences needed to be for a child to categorize the sentences as spoken by 2 different talkers. The average spectral characteristics of 2 utterances (including their fundamental frequencies) needed to differ by at least 11%-16% (2-2.5 semitones) for normal-hearing children to perceive the voices as belonging to different talkers. Introducing differences in the linguistic content of the 2 sentences to be compared did not change performance. Although several children with cochlear implants performed similarly to normal-hearing children, most found the task very difficult. Pediatric cochlear implant users who scored above the group mean of 64% of words correct on a monosyllabic open-set word identification task categorized the voices more like children with normal hearing sensitivity. (+info)
Electrode interaction in pediatric cochlear implant subjects.
(75/786)
Multielectrode cochlear implants rely on differential stimulation of the cochlear nerve for presenting the brain with the spectral and timing information required to understand speech. In implant patients, the degree of overlap among cochlear nerve fibers stimulated by the different electrodes constitutes the electrode interaction. Electrode interaction degrades the spectral resolution of the implant's stimulus. We sought to define electrode interaction in a cohort of pediatric cochlear implant subjects as a function of both stimulus intensity and electrode location along the array. The 27 pediatric subjects that completed the study were implanted with either the Clarion Hi-Focus array with or without positioner, the Nucleus 24 Contour array, or the Nucleus 24 Straight array. All but two of the patients had congenital hearing loss, and none of the patients had meningitis prior to the onset of deafness. The cochlear nerve response was measured with the electrically evoked compound action potential (ECAP). A forward masking protocol was used such that a probe stimulus electrode remained fixed while a preceding masker was moved across the array. Electrode interaction was estimated by measuring the unmasked probe response minus the masked probe response. Three probe locations and three probe intensities were examined for each subject. At all probe locations, electrode interaction increased as probe intensity increased (p < 0.05). Interaction at the basal probe was less than that at either the middle or apical probe locations (p < 0.05), and significant correlation found between probe distance from the basal end of the array and electrode interaction (p < 0.001). These results demonstrate that in this cohort of pediatric subjects, electrode interaction depended on both stimulus intensity and probe location. Implications of these findings on future implant array design and current implant fitting strategies are discussed. The impact of electrode interaction on implant performance is yet to be elucidated. (+info)
Auditory training with spectrally shifted speech: implications for cochlear implant patient auditory rehabilitation.
(76/786)
After implantation, postlingually deafened cochlear implant (CI) patients must adapt to both spectrally reduced and spectrally shifted speech, due to the limited number of electrodes and the limited length of the electrode array. This adaptation generally occurs during the first three to six months of implant use and may continue for many years. To see whether moderate speech training can accelerate this learning process, 16 naive, normal-hearing listeners were trained with spectrally shifted speech via an eight-channel acoustic simulation of CI speech processing. Baseline vowel and consonant recognition was measured for both spectrally shifted and unshifted speech. Short daily training sessions were conducted over five consecutive days, using four different protocols. For the test-only protocol, no improvement was seen over the five-day period. Similarly, sentence training provided little benefit for vowel recognition. However, after five days of targeted phoneme training, subjects' recognition of spectrally shifted vowels significantly improved in most subjects. This improvement did not generalize to the spectrally unshifted vowel and consonant tokens, suggesting that subjects adapted to the specific spectral shift, rather than to the eight-channel processing in general. Interestingly, significant improvement was also observed for the recognition of spectrally shifted consonants. The largest improvement was observed with targeted vowel contrast training, which did not include any explicit consonant training. These results suggest that targeted phoneme training can accelerate adaptation to spectrally shifted speech. Given these results with normal-hearing listeners, auditory rehabilitation tools that provide targeted phoneme training may be effective in improving the speech recognition performance of adult CI users. (+info)
Predicting the effect of post-implant cochlear fibrosis on residual hearing.
(77/786)
Intracochlear scarring is a well-described sequela of cochlear implantation. We developed a mathematical model of passive cochlear mechanics to predict the impact that this might have upon residual acoustical hearing after implantation. The cochlea was modeled using lumped impedance terms for scala vestibuli (SV), scala tympani (ST), and the cochlear partition (CP). The damping of ST and CP was increased in the basal one half of the cochlea to simulate the effect of scar tissue. We found that increasing the damping of the ST predominantly reduced basilar membrane vibrations in the apex of the cochlea while increasing the damping of the CP predominantly reduced basilar membrane vibrations in the base of the cochlea. As long as intracochlear scarring continues to occur with cochlear implantation, there will be limitations on hearing preservation. Newer surgical techniques and electrode technologies that do not result in as much scar tissue formation will permit improved hearing preservation. (+info)
Models of deafness: cochlear implants in the Australian daily press.
(78/786)
This article examined a database of Australian daily newspapers on the terms cochlear implant and deaf children to investigate how journalists and columnists report competing models of deafness: as either "medical" (deafness is a condition to be cured) or "sociocultural" (deafness provides a way of life to be lived). The results from the cochlear implant search favored a medical model, but the results from the deaf children search were more balanced, with a slight preponderance of articles favoring the sociocultural model. A number of representative quotes from articles in each model are provided and discussion entered into as to the possible effects of the articles on public reactions to deafness and especially hearing parental responses to the birth of a deaf child and the life choices that this event presents them. (+info)
Effects of stimulation rate, mode and level on modulation detection by cochlear implant users.
(79/786)
In cochlear implant (CI) patients, temporal processing is often poorest at low listening levels, making perception difficult for low-amplitude temporal cues that are important for consonant recognition and/or speech perception in noise. It remains unclear how speech processor parameters such as stimulation rate and stimulation mode may affect temporal processing, especially at low listening levels. The present study investigated the effects of these parameters on modulation detection by six CI users. Modulation detection thresholds (MDTs) were measured as functions of stimulation rate, mode, and level. Results show that for all stimulation rate and mode conditions, modulation sensitivity was poorest at quiet listening levels, consistent with results from previous studies. MDTs were better with the lower stimulation rate, especially for quiet-to-medium listening levels. Stimulation mode had no significant effect on MDTs. These results suggest that, although high stimulation rates may better encode temporal information and widen the electrode dynamic range, CI patients may not be able to access these enhanced temporal cues, especially at the lower portions of the dynamic range. Lower stimulation rates may provide better recognition of weak acoustic envelope information. (+info)
Development of visual attention skills in prelingually deaf children who use cochlear implants.
(80/786)
OBJECTIVE: To determine the effects of length of cochlear implant use and other demographic factors on the development of sustained visual attention in prelingually deaf children and to examine the relations between performance on a test of sustained visual attention and audiological outcome measures in this population. DESIGN: A retrospective analysis of data collected before cochlear implantation and over several years after implantation. Two groups of prelingually deaf children, one >6 years old (N = 41) and one <6 years old (N = 47) at testing, were given an age-appropriate Continuous Performance Task (CPT). In both groups, children monitored visually presented numbers for several minutes and responded whenever a designated number appeared. Hit rate, false alarm rate, and signal detection parameters were dependent measures of sustained visual attention. We tested for effects of a number of patient variables on CPT performance. Multiple regression analyses were conducted to determine if CPT scores were related to performance on several audiological outcome measures. RESULTS: In both groups of children, mean CPT performance was low compared with published norms for normal-hearing children, and performance improved as a function of length of cochlear implant use and chronological age. The improvement in performance was manifested as an increase in hit rate and perceptual sensitivity over time. In the younger age group, a greater number of active electrodes predicted better CPT performance. Results from regression analyses indicated a relationship between CPT response criterion and receptive language in the younger age group. However, we failed to uncover any other relations between CPT performance and speech and language outcome measures. CONCLUSIONS: Our findings suggest that cochlear implantation in prelingually deaf children leads to improved performance on a test of sustained visual processing of numbers over 2 or more years of cochlear implant use. In preschool-age children who use cochlear implants, individuals who are more conservative responders on the CPT show higher receptive language scores than do individuals with more impulsive response patterns. Theoretical accounts of these findings are discussed, including cross-modal reorganization of visual attention and enhanced phonological encoding of visually presented numbers. (+info)