Design and fabrication of multichannel cochlear implants for animal research.
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The effectiveness of multichannel cochlear implants depends on the activation of perceptually distinct regions of the auditory nerve. Increased information transfer is possible as the number of channels and dynamic range are increased and electrical and neural interaction among channels is reduced. Human and animal studies have demonstrated that specific design features of the intracochlear electrode directly affect these performance factors. These features include the geometry, size, and orientation of the stimulating sites, proximity of the device to spiral ganglion neurons, shape and position of the insulating carrier, and the stimulation mode (monopolar, bipolar, etc.). Animal studies to directly measure the effects of changes in electrode design are currently constrained by the lack of available electrodes that model contemporary clinical devices. This report presents methods to design and fabricate species-specific customizable electrode arrays. We have successfully implanted these arrays in guinea pigs and cats for periods of up to 14 months and have conducted acute electrophysiological experiments in these animals. Modifications enabling long-term intracochlear drug infusion are also described. Studies using these scale model arrays will improve our understanding of how these devices function in human subjects and how we can best optimize future cochlear implants. (+info)
The development of Weinstein's noise sensitivity scale.
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Many studies have shown the significant correlation between noise annoyance and noise sensitivity identified by Weinstein's noise sensitivity scale (WNS). However, the validity of the scale has not been sufficiently assessed. This study was designed to investigate the validity of each question in WNS and to develop a more valid noise sensitivity measurement scale. A questionnaire study was conducted in a residential area along trunk roads in Kusatsu, Japan, and 301 responses were collected. In this paper, noise sensitivity was defined as the factor that induced individual variability in reactions caused by noise exposure and that is not affected by the noise exposure. The relationship between noise exposure and answers to each question in WNS was investigated by multiple logistic regression analysis, and the influence of response bias on the score of WNS was examined. The results showed that WNS contained some questions that were inappropriately related to noise exposure level and that the score was affected by response bias. The reported correlation between annoyance and the score of WNS could be confounded by noise exposure and response bias. A noise sensitivity measurement scale named WNS-6B was newly developed, excluding the biased questions from the original WNS and applying binary coding to six-response options in order to reduce the response bias. WNS-6B seemed to be more appropriate to assess noise sensitivity than the original scale. (+info)
The reliability of the noise sensitivity questionnaire in a cross-national analysis.
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Noise sensitivity is regarded as a relevant predictor for annoyance reactions. Since many studies have focused on noise sensitivity at an international level, the present analysis was conducted to detect national peculiarities concerning noise sensitivity. Using the approach of the generalizability theory, reliability of the noise sensitivity questionnaire was analyzed taking into consideration relevant facets assumed to contribute to the measurement error. A total of 126 individuals from seven European countries participated in this study. The reliability coefficients for the global noise sensitivity score ranged from 0.90 to 0.91. It was determined that the translated questionnaires are comparable. (+info)
The development of the noise sensitivity questionnaire.
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The existing questionnaires for determining the noise sensitivity of individuals provide information only about global noise sensitivity, although empirical data suggest that measuring noise sensitivity for different situations in daily life might be more logical. Therefore, the "Noise-Sensitivity-Questionnaire" (NoiSeQ) was developed to measure global noise sensitivity as well as the sensitivity of five domains of daily life, namely, leisure, work, habitation, communication, and sleep. The assessment of the measurement characteristics was based on the Generalizability (G) theory. The results of the G-study (N=66) proved that a single application of the questionnaire is sufficient for determining an individual's noise sensitivity. Furthermore, the ratings are age and gender independent. The subsequently conducted Decision (D)-study (N=288) provides information on the reliability of NoiSeQ. If the questionnaire is used for measuring global noise sensitivity, the reliability (relative and absolute G-coefficient) reaches a value above 0.90. According to ISO 10075-3, the questionnaire satisfies the precision level 1 "accurate measurement" in this case. The G-coefficients for all the subscales exceed the lower limit 0.70, with the exception of subscale leisure, which did not prove satisfactory. However, this subscale can reach a reliability of more than 0.70 if additional items are included. The validity of the instrument was proven for the subscales habitation (N=72) and work (N=72). In both the studies, the participants were asked to rate the annoyance in the presence of several rail and traffic noise scenarios. The subjects were characterized as low and high noise sensitive according to their sensitivity values obtained from NoiSeQ. In conclusion, a significant difference in annoyance rates was observed between the low and high noise sensitive groups for both the subscales habitation and work. This data support the validity of NoiSeQ. (+info)
Differential reductions in acoustic startle document the discrimination of speech sounds in rats.
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The intensity of a noise-induced startle response can be reduced by the presentation of an otherwise neutral stimulus immediately before the noise ("prepulse inhibition" or PPI). This effect has been used to study the detection of gaps and other stimuli, but has been applied infrequently to complex stimuli or the ability to discriminate among multiple stimuli. To address both issues and explore the potential of PPI, rats were presented a series of 5 tasks, most contrasting a pair of speech sounds. One of these (the "standard" stimulus) occurred frequently but rarely preceded the startle stimulus. The second occurred infrequently (as an "oddball") and always preceded a noise. In each such task, startle responses were inhibited more by the oddball than by the standard stimulus, usually within the first test. This suggests that PPI can be adapted to studies of the discrimination of speech and other complex sounds, and that this method can provide useful information on subjects' ability to discriminate with greater ease and speed than other methods. (+info)
Sound pressure distribution and power flow within the gerbil ear canal from 100 Hz to 80 kHz.
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Sound pressure was mapped in the bony ear canal of gerbils during closed-field sound stimulation at frequencies from 0.1 to 80 kHz. A 1.27-mm-diam probe-tube microphone or a 0.17-mm-diam fiber-optic miniature microphone was positioned along approximately longitudinal trajectories within the 2.3-mm-diam ear canal. Substantial spatial variations in sound pressure, sharp minima in magnitude, and half-cycle phase changes occurred at frequencies >30 kHz. The sound frequencies of these transitions increased with decreasing distance from the tympanic membrane (TM). Sound pressure measured orthogonally across the surface of the TM showed only small variations at frequencies below 60 kHz. Hence, the ear canal sound field can be described fairly well as a one-dimensional standing wave pattern. Ear-canal power reflectance estimated from longitudinal spatial variations was roughly constant at 0.2-0.5 at frequencies between 30 and 45 kHz. In contrast, reflectance increased at higher frequencies to at least 0.8 above 60 kHz. Sound pressure was also mapped in a microphone-terminated uniform tube-an "artificial ear." Comparison with ear canal sound fields suggests that an artificial ear or "artificial cavity calibration" technique may underestimate the in situ sound pressure by 5-15 dB between 40 and 60 kHz. (+info)
Use of perceptual weights to test a model of loudness summation.
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Leibold et al.[J. Acoust. Soc. Am. 121, 2822-2831 (2007)] examined the perceptual weight subjects assigned to individual components of a multitone complex while performing a loudness-matching task. Weights agreed with the Moore et al. loudness model [J. Audio Eng. Soc. 45, 224-237 (1997)], except when components were widely spaced in frequency. In an effort to account for the data, the just-noticeable-difference (jnd) for intensity discrimination was measured for each component and compared to the weight for that component. The model predicts greater improvement in intensity discrimination with increasing bandwidth than was observed in the data. jnds were not correlated with weights in the widest frequency-spacing condition. (+info)
Interventions to reduce high-volume portable headsets: "turn down the sound"!
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Two studies examined effects of interventions to reduce noise levels from portable stereo headphones. Study 1 examined the effectiveness of warning signs posted in and nearby public elevators with 567 passengers possessing a portable headphone (total N = 7,811). During a 9-day baseline, the mean percentage of headphones played at an observer-audible level was 85%. During a subsequent 6-day warning sign phase, the mean percentage of audible headphones declined to 59%, which increased to a mean of 76% during a second baseline phase (5 days). Study 2 assessed the impact of a student confederate who lowered his or her observer-audible headphone volume at the polite request of a second student confederate. Of the 4,069 elevator passengers, 433 possessed a portable headset. The mean percentage of observer-audible headphones during a 4-day baseline was 85%. Subsequently, a 5-day modeling intervention reduced audible volumes to a mean of 46%. During a second baseline phase of 4 days, the mean level was 77%, and during reintroduction of the modeling phase (9 days) the mean level was 42%. The modeling intervention was significantly more effective with women (53% compliance) than men (29% compliance). (+info)