ISSN:0196-0202    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

This article provides a review of recent developments in our understanding of how cochlear nonlinearity affects sound perception and how a loss of the nonlinearity associated with cochlear hearing impairment changes the way sounds are perceived. The response of the healthy mammalian basilar membrane (BM) to sound is sharply tuned, highly nonlinear, and compressive. Damage to the outer hair cells (OHCs) results in changes to all three attributes: in the case of total OHC loss, the response of the BM becomes broadly tuned and linear. Many of the differences in auditory perception and performance between normal-hearing and hearing-impaired listeners can be explained in terms of these changes in BM response. Effects that can be accounted for in this way include poorer audiometric thresholds, loudness recruitment, reduced frequency selectivity, and changes in apparent temporal processing. All these effects can influence the ability of hearing-impaired listeners to perceive speech, especially in complex acoustic backgrounds. A number of behavioral methods have been proposed to estimate cochlear nonlinearity in individual listeners. By separating the effects of cochlear nonlinearity from other aspects of hearing impairment, such methods may contribute towards identifying the different physiological mechanisms responsible for hearing loss in individual patients. This in turn may lead to more accurate diagnoses and more effective hearing-aid fitting for individual patients. A remaining challenge is to devise a behavioral measure that is sufficiently accurate and efficient to be used in a clinical setting.

ISSN:0196-0202    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Otoacoustic emissions (OAEs) have become a commonly used clinical tool for assessing cochlear health status, in particular, the integrity of the cochlear amplifier or motor component of cochlear function. Predicting hearing thresholds from OAEs, however, remains a research challenge. Models and experimental data suggest that there are two mechanisms involved in the generation of OAEs. For distortion product, transient, and high-level stimulus frequency emissions, the interaction of multiple sources of emissions in the cochlea leads to amplitude variation in the composite ear canal signal. Multiple sources of emissions complicate simple correlations between audiometric test frequencies and otoacoustic emission frequencies. Current research offers new methods for estimating the individual components of OAE generation. Input-output functions and DP-grams of the nonlinear component of the 2f2-f2DPOAE may ultimately show better correlations with hearing thresholds. This paper reviews models of OAE generation and methods for estimating the contribution of source components to the composite emission that is recorded in the ear canal. The clinical implications of multiple source components are discussed.

ISSN:0196-0202    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

A useful and convenient means to analyze the radio frequency (RF) signals being sent by a speech processor to a cochlear implant would be to actually capture and display them with appropriate software. This is particularly useful for development or diagnostic purposes. sCILab (Swiss Cochlear Implant Laboratory) is such a PC-based software tool intended for the Nucleus family of Multichannel Cochlear Implants. Its graphical user interface provides a convenient and intuitive means for visualizing and analyzing the signals encoding speech information. Both numerical and graphic displays are available for detailed examination of the captured CI signals, as well as an acoustic simulation of these CI signals. sCILab has been used in the design and verification of new speech coding strategies, and has also been applied as an analytical tool in studies of how different parameter settings of existing speech coding strategies affect speech perception. As a diagnostic tool, it is also useful for troubleshooting problems with the external equipment of the cochlear implant systems.

ISSN:0196-0202    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

ObjectiveThe objectives of this study were to characterize the effects of presentation level on speech recognition in quiet by cochlear implant users with the Nucleus 22 SPEAK and Clarion v1.2 CIS speech-processing strategies, and to relate speech recognition at low presentation levels to stimulus audibility as measured by sound field thresholds. It was hypothesized that speech recognition performance in both Nucleus SPEAK and Clarion CIS participants would decrease as presentation level was decreased below 50 to 60 dBA, due to audibility limitations. However, it was expected that such level effects would be less severe in CIS participants than in SPEAK participants because the Clarion v1.2 device encodes a wider acoustic dynamic range (up to 60 dB) than the Nucleus 22 device (30 dB).DesignPerformance-intensity (P-I) functions for vowels, consonants and sentences in quiet were obtained from each participant. P-I functions incorporated speech levels of 70, 60, 50, 40 and 30 dBA. Subjects used their clinical speech processor maps and adjusted the loudness (volume/sensitivity) controls on their processors so that speech presented at 60 dBA was comfortably loud. Maps were created using default clinical procedures and were not adjusted to optimize sound field thresholds. Sound field thresholds and dynamic ranges were measured for warbled pure tones with frequencies of 250 to 6000 Hz.ResultsConsonant and sentence recognition showed strong level effects for both SPEAK and CIS participants, with performance decreasing substantially at levels below 50 dBA in most individuals. Vowel recognition showed weaker level effects. For all three speech materials, SPEAK and CIS participants demonstrated similar mean performance at 70 dBA; however, SPEAK participants showed larger reductions in performance than CIS participants with decreasing level. Sound field thresholds were more sensitive for CIS participants than for SPEAK participants, supporting the hypothesis that performance differences were related to audibility.ConclusionsCochlear implant listeners are unable to maintain good speech recognition at low presentation levels due to reduced stimulus audibility, and this may significantly limit their ability to communicate in daily life. It is likely that audibility differences between SPEAK and CIS participants in the present study can be attributed at least partly to differences in the acoustic dynamic range used by the respective processors. However, several additional factors may have contributed to differences in audibility and perception of soft speech among individual listeners with both devices. These include the minimum and maximum electrical stimulation levels specified in participants’ maps and the speech processor sensitivity setting used for testing.

ISSN:0196-0202    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

ObjectiveTo compare the magnitudes of the steady-state responses evoked by several types of stimuli, and the times required to recognize these responses as significant.DesignIn the first two experiments, we examined auditory steady-state responses to pure tones, broadband noise and band-limited noise. The stimuli were amplitude modulated in the 75 to 100 Hz range with sinusoidal or exponential envelopes. A third experiment investigated the effects of exponential envelopes on the responses to broadband noise. The final experiment examined auditory steady-state responses evoked by rapidly presented transient stimuli, such as clicks, brief tones and brief noise-bursts. All stimuli were presented dichotically at intensities 30 to 50 dB above behavioral thresholds. The subjects were adults, who drowsed or slept during the recording sessions.ResultsThe responses to the noise were larger than the responses to the tones. At an intensity of 32 dB nHL, the average amount of time needed to obtain significant responses for the amplitude-modulated noise was 43 sec and the maximum time was 2 minutes. The average time for pure tone stimuli was approximately 2 minutes but 25% of the responses remained undetected after 5 minutes. Combining the responses to all the frequency-specific stimuli showed results similar to using noise stimuli. Using exponential envelopes did not increase response amplitudes for noise stimuli. At 45 dB nHL, the steady-state responses to clicks and other transient stimuli were larger than responses to the broadband noise. The average time to detect steady-state responses to transient stimuli was approximately 20 sec, which was a little faster than for amplitude modulated noise.ConclusionsAuditory steady-state potentials evoked by amplitude modulated noise or transient stimuli might be useful in providing rapid and objective tests of hearing during screening procedures. Another approach might be to record responses to multiple frequency-specific stimuli and to evaluate the combined responses for a rapid indication that some hearing is present.

ISSN:0196-0202    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

ObjectiveThe purpose of this experiment was to systematically examine hearing aid benefit as measured by speech recognition and self-assessment methods across omnidirectional and directional hearing aid modes. These data were used to compare directional benefit as measured by speech recognition in the laboratory to hearing aid wearer's perceptions of benefit in everyday environments across full-time directional, full-time omnidirectional, and user selectable directional fittings. Identification of possible listening situations that resulted in different self reported hearing aid benefit as a function of microphone type was a secondary objective of this experiment.DesignFifteen adults with symmetrical, sloping sensorineural hearing loss were fitted bilaterally with in-the-ear (ITE) directional hearing aids. Measures of hearing aid benefit included the Profile of Hearing Aid Benefit (PHAB), the Connected Sentence Test (CST), the Hearing in Noise Test (HINT), and a daily use log. Additionally, two new subscales were developed for administration with the PHAB. These subscales were developed to specifically address situations in which directional hearing aids may provide different degrees of benefit than omnidirectional hearing aids. Participants completed these measures in three conditions: omnidirectional only (O), directional only with low-frequency gain compensation (D), and user-selectable directional/omnidirectional (DO).ResultsResults from the speech intelligibility in noise testing indicated significantly more hearing aid benefit in directional modes than omnidirectional. PHAB results indicated more benefit on the background noise subscale (BN) in the DO condition than in the O condition; however, this directional advantage was not present for the D condition. Although the reliability of the newly proposed subscales is as yet unknown, the data were interpreted as revealing a directional advantage in situations where the signal of interest was in front of the participant and a directional disadvantage in situations where the signal of interest was behind the listener or localization was required.ConclusionsLaboratory directional benefit is reflected in self-assessment measures that focus on listening in noise when the sound source of interest is in front of the listener. The use of a directional hearing aid mode; however, may have either a positive, a neutral, or a negative impact on hearing aid benefit measured in noisy situations, depending on the specific listening situation.

ISSN:0196-0202    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

ObjectiveMutations in theGJB2gene encoding connexin 26 (Cx26) protein are a major cause for nonsyndromic autosomal recessive and sporadic deafness. However, its contribution to hearing impairment in Switzerland remains undefined. To determine the frequency and type ofGJB2mutations in the Swiss hearing-impaired population diagnosed under the age of 2 yr and at 2 yr and older and to assess the effectiveness of denaturing high-performance liquid chromatography (DHPLC) in screening for mutation inGJB2.MethodsThirty-four patients with hearing impairment underwent mutation screening of the single coding exon ofGJB2with DHPLC followed by bidirectional sequencing to identify sequence alterations.ResultsGJB2 mutations were more common in children diagnosed with hearing impairment under the age of 2 yr compared to the group 2 yr and older. In patients under age 2 yr, 9 of 20 (45%) harbored 13GJB2mutations including a common 313del14nt mutation; four of these patients were homozygous or compound heterozygous forGJB2mutations. In contrast, 2 of 14 patients in the 2 yr and older group (14%) had a single mutation inGJB2. The 35delG mutation was exclusively found in 5 patients under the age of 2 yr. DHPLC for mutation screening was 100% sensitive and 83% specific for detecting sequence alterations inGJB2.ConclusionsIn Switzerland,GJB2mutations are a major cause of nonsyndromic hearing impairment in children under the age of 2. Similar to other populations,GJB2mutations are uncommon in the affected Swiss patients identified after 2 yr. Although 35delG mutation is common in the hearing-impaired children under the age of 2, it was absent in patients diagnosed with hearing impairment after the age of 2. DHPLC is a highly sensitive tool for detection ofGJB2mutations.

ISSN:0196-0202    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

ObjectiveThe primary objective of this study was to investigate the extent of comorbid auditory processing disorder (APD) in a group of adults with developmental dyslexia. An additional objective was to compare performance on auditory tasks to results from standardized tests of reading in an attempt to generate a clinically useful profile of developmental dyslexics with comorbid APD.DesignA group of eleven persons with developmental dyslexia and 14 age- and intelligence-matched controls participated in the study. Behavioral audiograms, 226-Hz tympanograms, and word recognition scores were obtained binaurally from all subjects. Both groups were administered the frequency-pattern test (FPT) and duration-pattern test (DPT) monaurally (30 items per ear) in both the left and right ear. Gap detection results were obtained in both groups (binaural presentation) using narrowband noise centered at 1 kHz in an adaptive two-alternative forced-choice (2-AFC) paradigm. The FPT, DPT, and gap detection results were analyzed for interaural (where applicable), intergroup, and intragroup differences. Correlations between performance on the auditory tasks and the standardized tests of reading were examined. Additive logistic regression models were fit to the data to determine which auditory tests proved to be the best predictors of group membership.ResultsThe persons with developmental dyslexia as a group performed significantly poorer than controls on both the FPT and DPT. Furthermore, the group differences were significant in both monaural conditions. On the FPT and DPT, five of the eleven participants with dyslexia performed below the widely used clinical criterion for APD of 70% correct in either ear. All five of these participants performed below criterion on the FPT, whereas four of the five additionally performed below 70% on the DPT. The data also were analyzed by fitting a series of stepwise logistic regression models, which indicated that gap detection did not significantly predict group membership, whereas the FPT and DPT were significant predictors. The addition of the FPT score after the DPT did not result in a significant change in the residual deviance.ConclusionsApproximately half of the participants with developmental dyslexia showed clinically significant diminished performance on the FPT and DPT indicative of APD. These results indicate that the percentage of persons with developmental dyslexia and comorbid APD may be substantial enough to warrant serious clinical considerations.

ISSN:0196-0202    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

The purpose of this project was to assess the degree to which a patient, after 1 wk of experience, could adapt to 3.2-mm and 6.8-mm basal shifts in the representation of speech. Only small deficits in performance were found after practice after the 3.2-mm shift. After practice after the 6.9-mm shift, scores on tests that emphasized amplitude envelope cues returned to baseline levels. Scores on vowel and sentence tests that emphasized frequency-based cues remained poor. Scores for “place,” however, showed some recovery. Vowel recognition may be the limiting factor in recognizing basally shifted speech.

ISSN:0196-0202    

出版商:OVID    

年代:2003

数据来源: OVID