Graeme Clark Collection
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ItemNo Preview AvailableFast inhibition alters first spike timing in auditory brainstem neurons(AMER PHYSIOLOGICAL SOC, 2004-10)Within the first processing site of the central auditory pathway, inhibitory neurons (D stellate cells) broadly tuned to tonal frequency project on narrowly tuned, excitatory output neurons (T stellate cells). The latter is thought to provide a topographic representation of sound spectrum, whereas the former is thought to provide lateral inhibition that improves spectral contrast, particularly in noise. In response to pure tones, the overall discharge rate in T stellate cells is unlikely to be suppressed dramatically by D stellate cells because they respond primarily to stimulus onset and provide fast, short-duration inhibition. In vivo intracellular recordings from the ventral cochlear nucleus (VCN) showed that, when tones were presented above or below the characteristic frequency (CF) of a T stellate neuron, they were inhibited during depolarization. This resulted in a delay in the initial action potential produced by T stellate cells. This ability of fast inhibition to alter the first spike timing of a T stellate neuron was confirmed by electrically activating the D stellate cell pathway that arises in the contralateral cochlear nucleus. Delay was also induced when two tones were presented: one at CF and one outside the frequency response area of the T stellate neuron. These findings suggest that the traditional view of lateral inhibition within the VCN should incorporate delay as one of its principle outcomes.
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ItemOptimizing dynamic range in children using the nucleus cochlear implant(LIPPINCOTT WILLIAMS & WILKINS, 2004-06)OBJECTIVE: The aim of this study was to investigate the benefits of the preprocessing scheme "Adaptive Dynamic Range Optimization" (ADRO) in children using Nucleus cochlear implants. Previous research with adults indicates improved speech perception in quiet and improved sound quality in everyday listening environments with the ADRO scheme. DESIGN: Children were given 4 wk of take-home experience with ADRO, with a minimum of 2 wk in which ADRO was "locked-in." After 1 wk of ADRO use and again after 4 wk of ADRO use, Bench-Kowal-Bamford (BKB) sentence perception in quiet at a low input level of 50 dB SPL (unweighted root mean square) and sentence perception in noise were compared with the child's everyday (Standard) program and the ADRO program. Children also rated the loudness of a variety of environmental sounds and indicated which program provided the best hearing in a variety of everyday listening situations. RESULTS: On average, BKB sentence perception in quiet at 50 dB SPL was significantly better with the ADRO program compared with the Standard program. The group mean improvement was 8.60%. Similarly, group mean scores for BKB sentences presented at 65 dB SPL in multitalker babble were significantly higher with the ADRO program (an improvement of 6.87%). The ADRO program was the preferred program in 46% of the listening situations, whereas the Standard program was preferred in 26% of situations. Everyday sounds were not unacceptably loud with ADRO. CONCLUSIONS: There was an ADRO benefit for this group of children in quiet and in noise. These findings suggest that young children would benefit from the ADRO programming option being locked in along with other processor settings in the SPrint processor once their MAP levels have stabilized. Some older children and teenagers may choose to use ADRO selectively for specific listening situations.
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ItemEffects of intracochlear factors on spiral ganglion cells and auditory brain stem response after long-term electrical stimulation in deafened kittens( 2000)Using an animal model, we have studied the response of the auditory brain stem to cochlear implantation and the effect of intracochlear factors on this response. Neonatally, pharmacologically deafened cats (100 to more than 180 days old) were implanted with a 4-electrode array in both cochleas. Then, the left cochlea of each cat was electrically stimulated for total periods of up to 1000 hours. After a terminal 14C-2-deoxyglucose (2DG) experiment, the fraction of the right inferior colliculus with a significant accumulation of 2DG label was calculated. Using 3-dimensional computer-aided reconstruction, we examined the cochleas of these animals for spiral ganglion cell (SGC) survival and intracochlear factors such as electrode positions, degeneration of the organ of Corti, and the degree of fibrosis of the scala tympani. The distribution of each parameter was calculated along the organ of Corti from the basal end. There was a positive correlation between SGC survival and the level of fibrosis in the scala tympani, and a negative correlation between SGC survival and the degree of organ of Corti degeneration. Finally, there was a negative correlation between the 2DG-labeled inferior colliculus volume fraction and the degree of fibrosis, particularly in the 1-mm region nearest the pair of electrodes, and presumably in the basal turn.
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ItemElectrode discrimination by early-deafened subjects using the Cochlear Limited multiple electrode cochlear implant( 2000)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.
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ItemThe effects of electrode position and stimulus period on the hearing sensations in a multiple-channel cochlear implant patient [Abstract]( 1981)Abstract not available due to copyright.
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ItemA multiple-channel cochlear implant: evaluation using speech tracking( 1981)Two totally deaf patients who had received multiple-channel cochlear implants were tested using a speech "tracking" procedure in which they had to repeat verbatim passages of connected discourse. Their performance was assessed by calculating the tracking rate (words per minute) each session. Testing was carried out under two conditions - lipreading along and lipreading in conjunction with a multiple-channel cochlear implant and laboratory speech processor. Lipreading with the cochlear implant increased the tracking rates by a factor of four for one patient and by a factor of two for the other when compared with lipreading alone.
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ItemVowel perception and hearing impairment( 1981)The perception of vowels by young hearing-impaired and normal-hearing children was investigated in two experimental versions, one which required the child ~o make discriminations among minimal pairs, the other which was based on free choice. Each version focused on three lists which comprised monosyllabic real word-pairs whose initial and final consonants were identical. These lists were constructed around high and low frequency components of vowel spectra in order to explore those acoustic aspects which have been hypothesized (Ling, 1978) as being maximally problematic in high-frequency hearing loss. Results indicated that the normal-hearing children, in contrast to the hearing-impaired, made virtually no errors in either task. The hearing-impaired children made significantly more errors in the free-choice task and in the lists whose vowels contained the highest frequency spectra and among those word-pairs which commenced with nonstops.....
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ItemPerceptual dissimilarity and discrimination studies using two-electrode stimulation with a multiple-channel cochlear implant patient [Abstract]( 1981)Abstract not available due to copyright.
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ItemA multiple-channel cochlear implant: an evaluation using nonsense syllables( 1981)A study using nonsense syllables has shown that a multiple-channel cochlear implant with speech processor is effective in providing information about, voicing and manner and to a lesser extent place distinctions. These distinctions supplement lipreading cues. Furthermore, the average percentage improvements in overall identification scores for multiple-channel electrical stimulation and lipreading compared to lipreading alone were 71% for a laboratory-based speech processor and 122 % for a wearable unit.
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ItemA multiple-channel cochlear implant: an evaluation using an open-set word test( 1981)Multiple-channel electrical stimulation of the hearing nerve in conjunction with speech reading 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 midfrequency range determined the site of electrode stimulation and current level.