Central auditory function

Central auditory disorders in children and adults have become more widely recognized in patients seen by otolaryngologists and audiologists. This article briefly defines those clinical entities, discusses the historic background of testing, and describes current and future test approaches to assessment of central auditory disorders.     

Central auditory fatigue.

The results of this study, based on evoked responses and single-neuronal responses, reveal that there is a central involvement in auditory fatigue. In these experiments, cochlear potentials (microphonic and whole-nerve action potential) and inferior colliculus electrical responses were simultaneously obtained before and after excessive sound exposure. In general, sound exposure produced a greater reduction of the collicular evoked responses than of the cochlear microphonics and action potentials. Recordings from single neurons support the evoked-response findings.     

Central auditory dysfunction.

The numerous tests applicable to the assessment of central deafness are briefly reviewed. It is likely that the more specific verbal and non-verbal tests, which assess more complex auditory function, will prove to be most useful in the assessment of these problems. We believe that the concept of a spectrum of clinical-anatomical types of central deafness is useful, namely, cortical, brainstem and more peripheral forms; a detailed study of an example of a predominantly brainstem type of central deafness is presented. An interdisciplinary approach which applies the methods of the audiologist, otolaryngologist, and neurologist to these patients is required to localize the site of the lesion, to detect and describe the deafness and to establish its etiology.     

Central auditory processing assessment

As the acoustic information travels within the central auditory nervous system, the processing of the signal undergoes several levels of serial and parallel "bottom-up" processing influenced by high level cognitive "top-down" processes. Because the multiple location of the operational sites, the central auditory deficits are frequently quite subtle and need a test battery approach to be identified. Each of the four principal processes has at least to be tested: the closure task, the dichotic ability, the temporal ordering task and the binaural interaction function. The purpose of this review is to provide an overview of the psychoacoustic test procedures of identifying lesions or dysfunction's in the central auditory system.     

中枢听觉加工损伤

人类的听觉系统分为外周听觉系统和中枢听觉加工系统（central auditory processing,CAP）,即由执行大脑听觉模式加工功能的神经系统组成。外周听觉系统的损伤比较容易诊断。与外周听觉系统不同的是,中枢听觉加工系统主要负责从外周听觉系统传人的神经冲动中提取有用的听觉信息。中枢听觉加工系统的损伤（central auditory processing disorders,CAPD）无法通过常规的听力测试检测出来。事实上,对多数CAPD孩子进行听力检查,结果都是完全正常的,有时甚至是过于敏感的。但是．这些孩子在特定的情景下对声音的加工会出现问题,这些问题突出表现在对中枢听觉功能的综合测试中。     

Central auditory and vestibular pathology

MR is the radiologic examination of choice when a patient's symptoms indicate the presence of some retrolabyrinthine pathology. CT dynamic studies now permit both heart and brain assessment for poor blood circulation problems of the hindbrain.     

Central auditory processing disorders in children

Central auditory processing disorders in children are introduced and defined. The article explains who should be evaluated and for what reasons. The evaluation process, test stimuli, and use of assessment findings are presented.     

Central auditory onset responses,and temporal asymmetries in auditory perception

Historically, central auditory responses have been studied for their sensitivity to various parameters of tone and noise burst stimulation, with response rate plotted as a function of the stimulus variable. The responses themselves are often quite brief, and locked in time to stimulus onset. In the stimulus amplitude domain, it has recently become clear that these responses are actually driven by properties of the stimulus' onset transient, and this has had important implications for how we interpret responses to manipulations of tone (or noise) burst plateau level. That finding was important in its own right, but a more general scrutiny of the available neurophysiological and psychophysical evidence reveals that there is a significant asymmetry in the neurophysiological and perceptual processing of stimulus onsets and offsets: sound onsets have a more elaborate neurophysiological representation, and receive a greater perceptual weighting. Hypotheses about origins of the asymmetries, derived independently from psychophysics and from neurophysiology, have in common a response threshold mechanism which adaptively tracks the ongoing level of stimulation.     

Central auditory tests and auditory nerve-brainstem evoked responses in multiple sclerosis

In 43 multiple sclerosis (MS) patients and an equal number of age- and sex-matched normal controls, auditory nerve-brainstem evoked responses (ABR), audiometric tests, central auditory tests (CAT) and clinical-neurological examinations were conducted. The CAT included rapid alternating speech perception, masking level differences to tones and to words and lateralization based on interaural time and intensity differences. The results in the MS group on the ABR and each of the CAT differed significantly from those in the control group. The ABR results and the lateralization test results were each abnormal in 50% of the MS patients. The ABR, CAT and clinical examination results were all mutually correlated. These findings are probably related to the fact that the demyelination in MS induces a decrease in impulse velocity, to temporal dispersion and to desynchrony of impulses in groups of affected axons and to the fact that the ABR and the CAT tests chosen are dependent on synchronous impulse firing and on the precise timing of the arrival of impulses from each ear at some brain centre. These tests may therefore contribute to neurological and to audiological diagnosis.     

Central auditory deficits associated with compromise of the primary auditory cortex

The subject of this study was a 46-year-old female who had suffered a cerebrovascular accident (CVA). Magnetic resonance imaging revealed damage in the area of the distribution of the middle cerebral artery involving most, if not all, of the primary auditory area of the left hemisphere. No auditory problems were noted prior to the CVA; however, following the CVA, the subject reported a number of auditory difficulties. Pure-tone thresholds were normal post-CVA, and performance on speech recognition testing was good in both ears if ample time was provided between a response and the presentation of the next test item. Duration pattern, intensity discrimination, and middle latency response test results were abnormal for both ears, and right ear deficits were evident on an auditory fusion test and two dichotic speech tests (digits and rhymes). This case is significant in that it demonstrates a good correlation between damage to known key auditory regions and central auditory test results.     

Central auditory deficits and temporal-lobe lesions.

The capacity of auditory pathways from the weak ear (ear with the suppressed score in a dichotic listening test) to transmit speech information to the cortical processing areas was examined on 10 patients with unilateral temporal-lobe lesions. Three lines of evidence were developed to suggest that auditory pathways from the weak ear and speech information presented to the weak ear are not completely suppressed during dichotic stimulation. Speech in the weak ear frequently interacts with competing speech information in the strong ear causing contrasting articulatory features from the two ears to be blended into a single response. Two models of unilateral central auditory deficits are discussed: ipsilateral-suppression and transmission-line.     

Central auditory processing in normal-hearing elderly adults

Central auditory and linguistic functions were assessed in a group of 25 essentially normal-hearing, cognitively intact elderly adults. Inclusion in the study required normal performance on the Mini-Mental State Examination Procedures used to evaluate central auditory performance included monosyllabic word lists, the Synthetic Sentence Identification-Ipsilateral Competing Message (SSI-ICM) test, the Dichotic Digits test and the Staggered Spondaic Word test. Linguistic competence was assessed utilizing subtests of the Boston Diagnostic Aphasia test and the Revised Token test. Results indicate that central auditory involvement can occur without a concomitant decline in peripheral hearing sensitivity, cognitive function, or linguistic competence. Our findings also suggest, that for the type of individuals included in this study, the SSI-ICM appears to be the most sensitive measure to changes in central auditory processing abilities with advancing age.     

Central auditory processing disorder (CAPD) in children with specific language impairment (SLI). Central auditory tests

The aim of this project is to use central auditory tests for diagnosis of central auditory processing disorder (CAPD) in children with specific language impairment (SLI), in order to confirm relationship between speech-language impairment and central auditory processing. We attempted to establish special dichotic binaural tests in Czech language modified for younger children. Tests are based on behavioral audiometry using dichotic listening (different auditory stimuli that presented to each ear simultaneously). The experimental tasks consisted of three auditory measures (test 1-3)-dichotic listening of two-syllable words presented like binaural interaction tests. Children with SLI are unable to create simple sentences from two words that are heard separately but simultaneously. Results in our group of 90 pre-school children (6-7 years old) confirmed integration deficit and problems with quality of short-term memory. Average rate of success of children with specific language impairment was 56% in test 1, 64% in test 2 and 63% in test 3. Results of control group: 92% in test 1, 93% in test 2 and 92% in test 3 (p<0.001). Our results indicate the relationship between disorders of speech-language perception and central auditory processing disorders.     

Central auditory function in a hearing-impaired white mouse

The dysfunction of the stria vascularis in the viable dominant spotting mutant mouse results in the reduction or the absence of the endocochlear potential. However, these mutants respond to an intense acoustic stimulus with a Preyer reflex (pinna twitch). This study used 14C autoradiography and electromyography to investigate central auditory responses in this mutant. There were three main findings: autoradiography demonstrated an increase in the metabolic rate within each of the central auditory nuclei during noise exposure compared with silence; electromyographic recordings indicated that there was no tensor tympani muscle reflex; the mutants were found to be susceptible to audiogenic seizures. It was concluded that the central auditory pathway of the viable dominant spotting mutant could be activated despite the abnormal strial function. Absence of the tensor tympani muscle reflex, together with auditory deprivation, might contribute to the susceptibility to audiogenic seizures.     

Central auditory battery testing in brain stem disease

The CAT scan and the BERA have revolutionized the practice of otology. There is a tendency to accept a negative scan report as indicating a lack of pathology. The authors have found cases where central battery testing has indicated progressing brain stem disease in the presence of a normal CAT scan. In one case, the abnormal test preceded a hemiplegia by two weeks. This raises the possibility of delaying or aborting an infarct if the correct diagnosis is made early.     

中枢听觉评估及其影响因素

听觉的中枢处理过程及中枢听功能障碍的表现和评估方法尚未被多数耳鼻咽喉科工作者及接受过资格培训的耳科医师所熟悉。本文就中枢听功能障碍的神经病理学基础、临床表现、评估方法及其影响因素进行介绍。