Scandinavian audiology. Supplementum最新文献

Auditory neuropathy is often characterized by normal thresholds, present otoacoustic emissions, poor speech discrimination, absent acoustic reflexes, absent or abnormal auditory brainstem response waveform, but normal late cortical potential. This paper describes an animal model that has many characteristics of auditory neuropathy. Chinchillas can be deprived of a significant portion of the neural inputs to the central auditory system by administering carboplatin, an antineoplastic agent that selectively destroys inner hair cells (IHCs) and type I auditory nerve fibers. Selective IHC loss has no effect on distortion product otoacoustic emissions or the cochlear microphonic potential, implying normal outer hair cell function. However, selective IHC loss causes the amplitude of the compound action potential to decrease in proportion to the degree of IHC loss. However, the threshold of the CAP shows little increase with mild to moderate IHC loss. Acoustically responsive auditory nerve fibers in ears with mild to moderate IHC loss have normal thresholds and tuning curves with narrowly tuned tips. Although the central auditory pathway is deprived of much of its sensory inputs, the amplitude of the local field potential in the auditory cortex was normal or enhanced, while those from the inferior colliculus were slightly reduced. The results are related to those of a patient with auditory neuropathy.

This article overviews some selected central auditory test procedures as well as some popular issues that surround them. Both behavioral and electrophysiologic central auditory tests are discussed in reference to their clinical value as judged by their sensitivity, specificity, administration time, and reliability. Also discussed are diagnostic trends that are noted on behavioral and electrophysiologic procedures. Relationships are drawn between children with auditory processing deficits associated with learning problems and individuals with neurological lesions of the central auditory nervous system.

This is a commentary on three key aspects of the management of central auditory processing disorders in children. It is an update on some selected approaches for the management of auditory processing problems. Auditory training techniques that are theoretically based and for which empirical data are emerging are addressed. The second part of our commentary deals with methods of enhancing acoustic speech signals. Discussions on clear speech, acoustic modifications of the listening environment, and the utilization of assistive listening devices are presented. The final part of the article reviews linguistic and cognitive interventions for people with auditory processing problems. Topics in this section include approaches to facilitate phonological awareness, vocabulary building, prosodic feature recognition, and use of metacognitive abilities.

We tested the hypothesis that tinnitus was due to excessive spontaneous activity in the central auditory system by seeking cerebral blood flow (CBF) changes that paralleled changes in the loudness of tinnitus in patients able to alter the loudness of their tinnitus. We found CBF changes in the left temporal lobe in patients with right ear tinnitus, in contrast to bilateral temporal lobe activity associated with stimulation of the right ear. The tones activated more extensive portions of the brain in patients than controls. We conclude that tinnitus is not cochlear in origin and associated with plastic transformations of the central auditory system. We suggest that tinnitus arises as a consequence of these aberrant new pathways and may be the auditory system analog to phantom limb sensations in amputees.

The use of cochlear implants to restore hearing in profoundly deaf children is increasing, with a trend toward earlier implantation. However, little is known about how auditory deprivation and subsequent implant use affects the maturing central auditory system. Previously reported results indicate that stimulation of the auditory system by a cochlear implant is sufficient to restore at least some aspects of central auditory pathway maturation, as reflected by age-related changes in the auditory evoked potentials. We review animal and human studies on sensory deprivation and report new results based on longitudinal evoked potentials data recorded from two individuals. Analyses show that age-related changes in the EPs may asymptote at levels very different from those found in the adult normal-hearing population. These results suggest that maturation of at least some aspects of central auditory system activity is limited by the onset and duration of the period of deafness prior to implantation.

The mammalian cochlea receives innervation from the central nervous system via two efferent systems: the lateral and the medial olivocochlear bundles. Advances in cochlear physiology have clarified the origins and terminations of these fibers. However, to date, while the functional significance of lateral efferents remains totally unknown, that of medial efferents is still controversial. The peripheral effects of medial olivocochlear system activation have been described, but the role of this inhibitory feedback onto the cochlea is still unclear. This overview summarizes the main results of several psychophysiological studies performed in humans dealing with the functional significance of medial olivocochlear efferents in hearing.

Auditory steady-state responses (SSRs) are believed to result from the superimposition of the middle latency responses (MLRs) evoked by individual stimuli. Our recent studies challenge this hypothesis in several regards. Surface-electrical recordings performed in 16 normal subjects showed that the prediction curves obtained by MLR linear addition failed to predict SSRs at rates other than 40 Hz. Amplitude and phase differences between actual and predicted responses point to the intervention of phenomena related to the recovery cycle of the neural networks underlying the SSR generation. A click train paradigm at a 40 Hz rate was utilized and an approximation to the response evoked by the last stimulus was obtained by an analytical handling. The most relevant feature of this response in comparison to the MLR was the appearance of an additional activity which could be related to the fast oscillations of auditory cortical neurons. Our findings suggest that the responses evoked by individual stimuli during steady-state stimulation change by increasing the repetition rate, thus contradicting the most widely accepted hypothesis of the MLR linear addition in the SSR generation.

Evoked otoacoustic emissions have been shown to be suppressed by sounds applied in the contralateral ear and this effect can be largely explained by the involvement of medial olivocochlear efferent fibers. Thus, EOAE recording during contralateral stimulation provides a non-invasive means of investigating auditory efferent system functioning in humans. The question remains, however, as to whether this test provides a tool, which could be useful in a variety of clinical applications. This review describes current clinical applications for this test, showing that it may prove useful for improving identification of retrocochlear pathologies. Some new areas are also identified. Methodological topics are discussed and suggestions for maximizing the value of this test are proposed.

The underlying assumption in the present study is that the individual's speech and hearing communicative ability is composed of three components, each corresponding to different functional systems of the brain: afferent functions (A) represent the auditory activity and sound perception largely corresponding to activity in the ascending auditory pathways. The central functions (C) include cortical auditory and language abilities controlled in parts of the left temporal lobe and subcortical centres. The efferent functions (E) consist of speech motor processes and articulation. A test battery of 20 tests measuring several aspects of afferent, central and efferent functions was applied to 11 hearing-impaired post-secondary school students and several control groups. All data were normalized with the normal materials as references. Individual communicative profiles were obtained from these primary data, which consisted of audiometric tests (tone and speech audiometry, impedance tests, brainstem response audiometry and phase audiometry), sound environmental tests with hearing aids (directional speech-in-noise, word localization, sound environment identification test), and language tests (reading tests, prosody, auditory memory and recall, phonology and articulation). Since the central functions cannot truly and directly be determined in hearing-imparied subjects, they were assessed under optimal listening conditions. Furthermore, central functions were estimated according to three different models: distributive, parallel model (model 1), multiplicative, serial model (model 2) and compensatory model (model 3). On the basis of these models, a three-component description of the communicative ability consisting of A,C and E functions was obtained. It was found that C and E functions were largely independent of the adult afferent functions, but C functions were negatively correctly to hearing in childhood. A preliminary comparison between the tests and a comparison between the models was performed by predicting benefit of hearing aid. Model 3 gave the best prediction. Beyond the three-component A,C, and E characterization of the students, a total communicative ability score could be calculated giving values from 37% to 79% of the normal mean. On the basis of the conceptual and statistical analyses, the test battery could be reduced to include tone 0-12 years, tone adults, word localization test (afferent); word chain, lecture test (central), articulatory test (efferent) and audiovisual test. The simple algorithm of adding the normalized loss of afferent (peripheral) function to the normalized results of the acoustic central tests seems to be promising for isolation for the central auditory capacity even in cases with peripheral impairment. It is concluded that a wider perspective is desirable in the diagnostic evaluation of the hearing-impaired individual in order to understand his communicative abilities and form a cornerstone in the planning of reha