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The auditory brainstem response (ABR) and middle latency response (MLR) are two sets of evoked potentials that have made major contributions to the field of diagnostic audiology. Many of these contributions were guided by clinical research audiologists. Though many of these auditory evoked potentials (AEPs) are still being used diagnostically by audiologists, there has been a steep decline in their popularity both clinically and in the research laboratory. This is indeed most unfortunate because these AEPs could and should be advancing our field and benefitting many patients. In this article, some critical research is overviewed that addresses some of the reasons why these AEPs (ABR and MLR) are not being utilized as frequently as they should be for neuroauditory assessments. Reflecting on our past when ABR and MLR were more commonly used can serve as a model for our future. Multiple applications and the diagnostic value of these AEPs are presented in an effort to convince audiologists that these electrophysiologic procedures should be revisited and reapplied in the clinic and research settings. It is argued that the dwindling use of ABR and MLR (and AEPs in general) in the field of audiology is not only remarkably premature but also lacks good scientific grounding. While on the other hand, if applied clinically, the value of these AEPs is both substantial and promising.

Background Self-reported hearing aid outcomes among older adults are variable and important to improve. The extent of the role of auditory processing in long-term hearing aid outcomes is not well understood.Purpose To determine how auditory processing abilities are related to self-reported hearing aid satisfaction and benefit along with either aided audibility alone or exploratory factors suggested by previous literature.Research Design Descriptive analyses and multiple regression analyses of cross-sectional self-reported outcomes.Study Sample Adult participants, >60 years (n = 78), fitted with bilateral hearing aids to treat symmetric, mild to moderate sensorineural hearing loss.Data Collection and Analysis Participants were recruited from a single audiology clinic to complete a series of questionnaires, behavioral assessments, and obtain data from their hearing aids, including real ear measures and data logging of hearing aid use. Multiple linear regressions were used to determine the amount of variance explained by predictive factors in self-reported hearing aid satisfaction and benefit. The primary predictive factors included gap detection threshold, spatial advantage score, dichotic difference score, and aided audibility. Exploratory factors included personality, self-efficacy, self-report of disability, and hearing aid use. All interpretations of statistical significance used p Results Gap detection threshold was a statistically significant predictor in both primary regression models with a medium effect size for satisfaction and a small effect size for benefit. When additional exploratory factors were included in the regression models with auditory processing abilities, gap detection and self-efficacy were both significant predictors of hearing aid satisfaction with medium effect sizes, explaining 10 and 17% of the variance, respectively. There were no medium effect sizes found for other predictor variables in either the primary or exploratory hearing aid benefit models. Additional factors were statistically significant in the models, explaining a small amount of variance, but did not meet the medium effect size criterion.Conclusion This study provides initial evidence supporting the incorporation of measures of gap detection ability and hearing aid self-efficacy into clinical practice for the interpretation of postfitting long-term hearing aid satisfaction.

There are still no valid, clinically feasible instruments to assess backward masking (BM), an auditory temporal processing (ATP) phenomenon. The aim of this study was to develop, standardize and present evidence of validity for a behavioral test for BM assessment. Young adults were submitted to a BM test (BMT), where they were asked to identify a 1000 Hz pure tone followed by a narrowband noise with interstimulus intervals of 0 to 400 ms and signal-to-noise ratio (SNR) between −20 and −30 dB. The correct response rate and target sound detection threshold were calculated, and the results compared with those of young adults with abnormal ATP tests and older adults. Diagnostic accuracy analyses were carried out. Young adults with normal ATP obtained an average correct response rate of 89 and 87% for SNR −20 and −30 dB, respectively, with average thresholds between 10 and 15 ms and no difference between the left and right ears. Results were more consistent at SNR −20 dB, and the best diagnostic accuracy was obtained for SNR −20 dB, with good specificity, but low sensitivity. Normative values were obtained for the BMT, which proved to be clinically feasible, with preliminary evidence of validity.

Background Interesting data and theories have emerged regarding auditory hallucinations (AHs) in patients with schizophrenia. The possibility that these patients may have changes in the anatomy of the auditory cortex and/or subcortical structures of the central auditory nervous system and present with deficits on audiological tests is important information to the audiology community. However, it seems clear that, in general, audiologists are not sufficiently aware of these findings. Purpose There are two main purposes of this article: (1) to educate audiologists about AHs related to schizophrenia and related issues, and (2) to encourage audiologists and hearing scientists to become involved in the evaluation and research of AHs. This fascinating disorder is one in which audiologists/hearing scientists are well suited to make a significant contribution. Research Design A review and synthesis of the literature was conducted. Relevant literature was identified through PubMed, Google Scholar, as well as independent book chapters and article searches. Keywords driving the searches were AHs, auditory illusions, verbal and musical hallucinations, schizophrenia, and central auditory disorders. Given the currency of the topic, the information collected was primarily between 1990 and 2020. Study Sample The review is organized around categorization, prevalence, models, mechanisms, anatomy, pathophysiology, and audiological correlates related to AHs. Data Collection and Analysis Searches were conducted using well-known search engines and manual searches by each author. This information on AHs was then analyzed collectively by the authors for useful background and relevance, as well as important for the field of audiology. Results Several anatomical, physiological, and functional imaging studies have shown compromise of the auditory cortex in those with schizophrenia and AHs. Potentially related to this, are studies that demonstrated sub-par performance on behavioral audiologic measures for this unique clinical population. These findings align well with the kind of hearing disorder for which audiologists are well-trained to make significant contributions. Conclusion Neurobiological and audiological evidence is accumulating on patients with schizophrenia and AH potentially rendering it as both an auditory and psychiatric disorder. Audiologists should consider expanding their horizon and playing a role in the clinical investigation of this disorder.

Background Dichotic listening occurs when one attends to different acoustical messages presented simultaneously to both ears. This is important for understanding speech in compromised listening situations, such as background noise. Deficits in dichotic listening can be remediated by participating in auditory training. We present two patients with binaural integration deficits who underwent dichotic interaural intensity difference (DIID) training. Purpose The purpose of this investigation is to demonstrate improvement of dichotic listening deficits following DIID training in neurological patients seen clinically for hearing issues. Research Design This was a case series utilizing a pre- and posttreatment design. Study Sample This case series utilized two female participants who demonstrated binaural integration deficits during an auditory processing evaluation. Intervention The participants underwent a pretraining auditory processing evaluation and functional magnetic resonance imaging (fMRI). Participants then underwent 12, 30-minute DIID training sessions followed by posttreatment auditory processing evaluations and fMRI. Data Collection and Analysis Data was collected at the pretreatment appointment and then immediately following the completion of the training. Results Each patient demonstrated varying degrees of improvement on the posttreatment assessment. Case 1 showed significant improvement on the Speech-in-Noise-Revised (SPIN-R) test. fMRI showed changes in activation patterns following training. Case 2 demonstrated improved scores on the Dichotic Digits Test and SPIN-R and increased activation of the calcarine sulcus following training. Conclusion Dichotic training can be an efficacious treatment for binaural integration deficits and may show evidence of improving speech understanding in noise. This case series demonstrates a promising therapy to help patients improve auditory function by improving dichotic listening skills.

BackgroundThe planum temporale (PT) is well known for its classic “pie-shaped” morphology. The aim of this study is to create a taxonomy of PT morphological features to improve its sometimes difficult identification and differentiation from surrounding structures.Material and methodsA total of 50 normal, high-resolution T1-weighted brain MRIs (100 hemispheres) were obtained from the Open Access Series of Imaging Studies (OASIS) repository. Ages ranged from 18 to 57 years.MethodsA 3D cortical surface mesh (grey matter) was generated using neuroimaging software. The PT was isolated based on pre-defined criteria and stratified into different classifications. Quantitative measurements were also taken.ResultsA total of four PT configurations were identified: (1) Pie-shaped [45%], 508.8 mm2; (2) Trapezoid-shaped [27%], 540.4 mm2, (3) Rectangular-shaped [19%], 477.7 mm2; and (4) Amorphous/none [9%], not calculable. The trapezoid-shaped PT category occurred significantly more often in females.ConclusionsThe proposed classification is the first step in creating a comprehensive.

Purpose: This study aimed to determine whether onset–offset N1–P2 auditory evoked responses differ in amplitude, latency, and offset-to-onset trough-to-peak N1–P2 amplitude ratios (OOAR) between normal hearing (NH) sensitivity and moderate high-frequency sensorineural hearing loss (HFSNHL) groups when stimuli target regions of peripheral hearing sensitivity where the groups are in the normal range (i.e., 500 Hz) versus where they differ regarding presence of hearing loss (i.e., 4000 Hz). Method: Onset–offset N1–P2 auditory evoked responses were measured from 10 participants with normal hearing sensitivity and seven participants with moderate HFSNHL using 500-Hz and 4000-Hz narrowband noise (NBN) stimuli. Stimuli were 2000 ms with 40-ms rise-fall times presented at 50 dB SL referenced to stimulus behavioral thresholds. Amplitudes and latencies were analyzed for N1 and P2 onset and offset components via repeated measures analysis of variance (ANOVA). OOARs were compared between groups using one-way ANOVA and across stimuli per group using paired samples t tests. Results: Despite dB SPL stimulus presentation differences between groups, there were no significant differences in individual/absolute amplitude and latency waveform components between groups for either stimulus. Derived comparative calculations of OOAR for 4000-Hz NBN were significantly larger ( p < .025; NH: .39; HFSNHL: .62) for the group with HFSNHL than the group with NH sensitivity; 500-Hz NBN OOAR did not reach significance. OOARs revealed no significant difference between stimuli for the group with normal hearing sensitivity, with .38 OOAR for both stimuli ( p = .961). OOAR comparisons for the HFSNHL group across stimuli were significant ( p = .012), with the 4000-Hz NBN OOAR being nearly double the size of the 500-Hz NBN OOAR. Conclusions: OOARs may provide insight to the balance of excitatory and inhibitory neural firing in the central auditory nervous system (CANS). Larger OOARs may be a biomarker of reduced CANS inhibition, perhaps indicative of a homeostatic central auditory gain mechanism.

Passive electrophysiological protocols, such as the middle latency response and speech auditory brainstem response, are often advocated in the objective assessment of central auditory processing disorder (CAPD). However, few established electrophysiological protocols exist for CAPD assessment that have patients participate in active tasks which more closely approximate real-world listening. To this end, the present study used a discrimination task (i.e., oddball paradigm) to measure an enhancement of the auditory late response (N1-P2) that occurs when participants direct their auditory attention toward speech arising from an unexpected spatial location.To establish whether N1-P2 is enhanced when auditory attention is directed toward an unexpected location during a two-word discrimination task. In addition, it was also investigated whether any enhancements in this response were contingent on the stimulus being counted as part of the oddball paradigm.Prospective study with a repeated measures design.Ten normal hearing adults, with an age range of 18–24 years.The N1 and P2 latencies and peak-to-peak amplitudes were recorded during a P300 paradigm. A series of repeated measures of analysis of variance and a correlation analysis was performed.There was a significant effect of stimulus location, in which words arising from the unexpected location showed a larger N1-P2 peak-to-peak amplitude and an earlier N1 latency. This effect was seen regardless of whether or not participants had to count the word total in memory.These findings suggest that spatial enhancement of the N1-P2 is a fairly robust phenomenon in normal hearing adult listeners. Additional studies are needed to determine whether this enhancement is absent or reduced in patients with CAPD.

Purpose Clinical use of electrophysiologic measures has been limited to use of brief stimuli to evoke responses. While brief stimuli elicit onset responses in individuals with normal hearing and normal central auditory nervous system (CANS) function, responses represent the integrity of a fraction of the mainly excitatory central auditory neurons. Longer stimuli could provide information regarding excitatory and inhibitory CANS function. Our goal was to measure the onset–offset N1–P2 auditory evoked response in subjects with normal hearing and subjects with moderate high-frequency sensorineural hearing loss (HFSNHL) to determine whether the response can be measured in individuals with moderate HFSNHL and, if so, whether waveform components differ between participant groups. Method Waveforms were obtained from 10 participants with normal hearing and seven participants with HFSNHL aged 40–67 years using 2,000-ms broadband noise stimuli with 40-ms rise–fall times presented at 50 dB SL referenced to stimulus threshold. Amplitudes and latencies were analyzed via repeated-measures analysis of variance (ANOVA). N1 and P2 onset latencies were compared to offset counterparts via repeated-measures ANOVA after subtracting 2,000 ms from the offset latencies to account for stimulus duration. Offset-to-onset trough-to-peak amplitude ratios between groups were compared using a one-way ANOVA. Results Responses were evoked from all participants. There were no differences between participant groups for the waveform components measured. Response × Participant Group interactions were not significant. Offset N1–P2 latencies were significantly shorter than onset counterparts after adjusting for stimulus duration (normal hearing: 43 ms shorter; HFSNHL: 47 ms shorter). Conclusions Onset–offset N1–P2 responses were resistant to moderate HFSNHL. It is likely that the onset was elicited by the presentation of a sound in silence and the offset by the change in stimulus envelope from plateau to fall, suggesting an excitatory onset response and an inhibitory-influenced offset response. Results indicated this protocol can be used to investigate CANS function in individuals with moderate HFSNHL. Supplemental Material https://doi.org/10.23641/asha.14669007

Objectives Adults with hearing loss report a wide range of hearing aid satisfaction that does not significantly correlate to degree of hearing loss. It is not clear which auditory behavioral factors do contribute to hearing aid satisfaction. While poor speech understanding in noise is known to contribute to dissatisfaction, there are many categories of this type of assessment. The purpose of this systematic review is to answer the question, "Are behavioral pre-fitting measures using speech and nonspeech materials related to hearing aid satisfaction among adults?" Design Six electronic databases were searched to find peer-reviewed studies published before June 2020. The included studies reported on the relationship between auditory behavioral measures and hearing aid satisfaction alone or globally with other outcome domains among adults with hearing loss. Six types of behavioral prefitting measures were evaluated: speech recognition in quiet (% correct), speech recognition in noise (% correct), reception thresholds for speech-in-noise, speech-based subjective ratings, dichotic speech tests, and tests using nonspeech material. Each relevant study was independently reviewed by two reviewers. Methodological quality was evaluated in each included study using the American Speech-Language-Hearing Association's level of evidence ratings. Results There were 1342 articles identified in the systematic review process. After duplicates were removed and specific inclusion criteria were applied, 21 studies were included. All studies included had a 0 to 4 methodological quality rating indicating weak to moderate internal validity. The tests that showed potential for clinical application due to significant correlations with satisfaction were the QuickSIN, the synthetic sentence identification, the hearing in noise test, and the acceptable noise level test. Audibility, as measured by degree of hearing loss, was not significantly correlated to hearing aid satisfaction in the 13 studies that reported on this measure. Conclusions Based on this review, results indicated that speech-in-noise tests had the highest associations to hearing aid satisfaction, suggesting a greater role for assessment of speech-in-noise perception in auditory rehabilitation. This is an important finding for clinical practice, given that audibility was not a significant factor in predicting satisfaction. Overall, the results from this review show a need for well-designed, high-quality, prospective studies assessing the predictive value of prefitting measures on hearing aid satisfaction with current hearing aid models.

The middle latency response (MLR) first came to light as an auditory evoked potential in 1958. Since then, it has aroused substantial interest and investigation by clinicians and researchers alike. In recent history, its use and popularity have dwindled in tandem with various other auditory evoked potentials in audiology. One area for which MLR research and application has been overlooked is its potential value in measuring the neural integrity of the auditory thalamocortical pathway. In a broader sense, the MLR, when combined with the auditory brain stem response, can provide information concerning the status of much of the central auditory system pathways. This review is intended to provide information concerning the MLR as a measure of central auditory function for the reader to consider.To review and synthesize the scientific literature regarding the potential value of the MLR in assessing the integrity of the central auditory system and to provide the reader an informed perspective on the value of the MLR in this regard. Information is also provided on the MLR generator sites and fundamental characteristics of this evoked potential essential to its clinical and or research application.A systematic review and synthesis of the literature focusing on the MLR and lesions of the central auditory system.Studies and individual cases were reviewed and analyzed that evidenced documented lesions of the central auditory nervous system.The authors searched and reviewed the literature (journal articles, book chapters, and books) pertaining to central auditory system lesion effects on the MLR.Although findings varied from study to study, overall, the MLR was reasonably sensitive and specific to neurological compromise of the central auditory system. This finding is consistent with the generator sites of this evoked potential.The MLR is a valuable tool for assessing the integrity of the central auditory system. It should be of interest to the clinician or researcher who focuses their attention on the function and dysfunction of the higher auditory system.

Purpose and Conclusion This letter to the editor is a rebuttal to Vermiglio's “The Gold Standard and Auditory Processing Disorder” (2018). We identify several faulty premises, inconsistent use of t...

Pediatric central auditory processing disorder (CAPD) is frequently comorbid with other childhood disorders. However, few studies have examined the relationship between commonly used CAPD, language, and cognition tests within the same sample.The present study examined the relationship between diagnostic CAPD tests and “gold standard” measures of language and cognitive ability, the Clinical Evaluation of Language Fundamentals (CELF) and the Wechsler Intelligence Scale for Children (WISC).A retrospective study.Twenty-seven patients referred for CAPD testing who scored average or better on the CELF and low average or better on the WISC were initially included. Seven children who scored below the CELF and/or WISC inclusion criteria were then added to the dataset for a second analysis, yielding a sample size of 34.Participants were administered a CAPD battery that included at least the following three CAPD tests: Frequency Patterns (FP), Dichotic Digits (DD), and Competing Sentences (CS). In addition, they were administered the CELF and WISC. Relationships between scores on CAPD, language (CELF), and cognition (WISC) tests were examined using correlation analysis.DD and FP showed significant correlations with Full Scale Intelligence Quotient, and the DD left ear and the DD interaural difference measures both showed significant correlations with working memory. However, ∼80% or more of the variance in these CAPD tests was unexplained by language and cognition measures. Language and cognition measures were more strongly correlated with each other than were the CAPD tests with any CELF or WISC scale. Additional correlations with the CAPD tests were revealed when patients who scored in the mild–moderate deficit range on the CELF and/or in the borderline low intellectual functioning range on the WISC were included in the analysis.While both the DD and FP tests showed significant correlations with one or more cognition measures, the majority of the variance in these CAPD measures went unexplained by cognition. Unlike DD and FP, the CS test was not correlated with cognition. Additionally, language measures were not significantly correlated with any of the CAPD tests. Our findings emphasize that the outcomes and interpretation of results vary as a function of the subject inclusion criteria that are applied for the CELF and WISC. Including participants with poorer cognition and/or language scores increased the number of significant correlations observed. For this reason, it is important that studies investigating the relationship between CAPD and other domains or disorders report the specific inclusion criteria used for all tests.

The pure-tone audiogram, though fundamental to audiology, presents limitations, especially in the case of central auditory involvement. Advances in auditory neuroscience underscore the considerably larger role of the central auditory nervous system (CANS) in hearing and related disorders. Given the availability of behavioral audiological tests and electrophysiological procedures that can provide better insights as to the function of the various components of the auditory system, this perspective piece reviews the limitations of the pure-tone audiogram and notes some of the advantages of other tests and procedures used in tandem with the pure-tone threshold measurement.To review and synthesize the literature regarding the utility and limitations of the pure-tone audiogram in determining dysfunction of peripheral sensory and neural systems, as well as the CANS, and to identify other tests and procedures that can supplement pure-tone thresholds and provide enhanced diagnostic insight, especially regarding problems of the central auditory system.A systematic review and synthesis of the literature.The authors independently searched and reviewed literature (journal articles, book chapters) pertaining to the limitations of the pure-tone audiogram.The pure-tone audiogram provides information as to hearing sensitivity across a selected frequency range. Normal or near-normal pure-tone thresholds sometimes are observed despite cochlear damage. There are a surprising number of patients with acoustic neuromas who have essentially normal pure-tone thresholds. In cases of central deafness, depressed pure-tone thresholds may not accurately reflect the status of the peripheral auditory system. Listening difficulties are seen in the presence of normal pure-tone thresholds. Suprathreshold procedures and a variety of other tests can provide information regarding other and often more central functions of the auditory system.The audiogram is a primary tool for determining type, degree, and configuration of hearing loss; however, it provides the clinician with information regarding only hearing sensitivity, and no information about central auditory processing or the auditory processing of real-world signals (i.e., speech, music). The pure-tone audiogram offers limited insight into functional hearing and should be viewed only as a test of hearing sensitivity. Given the limitations of the pure-tone audiogram, a brief overview is provided of available behavioral tests and electrophysiological procedures that are sensitive to the function and integrity of the central auditory system, which provide better diagnostic and rehabilitative information to the clinician and patient.

Objective: The purpose of this review was to describe and differentiate clinical syndromes caused by lesions of the central auditory nervous system (CANS). Design: Relevant literature was identified through Pubmed and Google Scholar searches using the key terms: central deafness, auditory agnosia, word deafness and cortical deafness. Given the authors' intent to review past and current perspectives on central deafness, no publication date range was imposed. Study sample: The review is organised around complete central deafness (CCD), central deafness (CD), word deafness and nonverbal agnosia (NVA), including anatomy and pathophysiology, symptom profile and audiological findings. Four case studies are presented to demonstrate the clinical correlates of CD. Conclusions: Central deafness is a rare condition typically resulting from bilateral compromise of the CANS. The closer to the auditory cortex bilateral lesions are located, the greater the probability of CD. A variety of symptoms present with or appear subsequent to CD, including tinnitus, hallucinations, voice changes and hypersensitivity to sounds (if heard by the patient), as well as diverse neurological symptoms depending on the non-auditory areas of the brain that may also be involved. Thorough and appropriate audiological testing is critical to accurately diagnose CD and its variants.

OBJECTIVES In a cross-sectional study of human immunodeficiency virus (HIV)-infected adults, the authors showed lower distortion product otoacoustic emissions (DPOAEs) in HIV+ individuals compared with controls as well as findings consistent with a central auditory processing deficit in HIV+ adults on antiretroviral therapy. The authors hypothesized that HIV+ children would also have a higher prevalence of abnormal central and peripheral hearing test results compared with HIV- controls. DESIGN Pure-tone thresholds, DPOAEs, and tympanometry were performed on 244 subjects (131 HIV+ and 113 HIV- subjects). Thirty-five of the HIV+, and 3 of the HIV- subjects had a history of tuberculosis treatment. Gap detection results were available for 18 HIV- and 44 HIV+ children. Auditory brainstem response results were available for 72 HIV- and 72 HIV+ children. Data from ears with abnormal tympanograms were excluded. RESULTS HIV+ subjects were significantly more likely to have abnormal tympanograms, histories of ear drainage, tuberculosis, or dizziness. All audiometric results were compared between groups using a two-way ANOVA with HIV status and ear drainage history as grouping variables. Mean audiometric thresholds, gap detection thresholds, and auditory brainstem response latencies did not differ between groups, although the HIV+ group had a higher proportion of individuals with a hearing loss >25 dB HL in the better ear. The HIV+ group had reduced DPOAE levels (p < 0.05) at multiple frequencies compared with HIV- subjects. No relationships were found between treatment regimens or delay in starting treatment and audiological parameters. CONCLUSIONS As expected, children with HIV+ were more likely to have a history of ear drainage, and to have abnormal tympanograms. Similar to the adult findings, the HIV+ group did not show significantly reduced audiometric thresholds, but did have significantly lower DPOAE magnitudes. These data suggest that (1) HIV+ children often have middle ear damage which complicates understanding the direct effects of HIV on the hearing system, and (2) even when corrected for confounders DPOAEs were lower in the HIV+ group. Previous studies suggest ototoxicity from antiretroviral drugs is an unlikely cause of the reduced DPOAE magnitudes. Other possibilities include effects on efferent pathways connecting to outer hair cells or a direct effect of HIV on the cochlea.

BackgroundThe angular gyrus (AG) is an association area of the human cerebral cortex that plays a role in several processes, including auditory function. However, the precise anatomical location of the AG is not entirely clear. There are two common approaches for locating the AG based on gyral and sulcal landmarks: the ‘parallel’ and ‘count-back’ methods (as termed by the present authors). These two techniques do not always point to the same location on the cortex, thus making the macroanatomical locus of the AG rather ambiguous.MaterialTwenty high-resolution brain MRIs of normal, right-handed human subjects chosen from an online database (OASIS).MethodsMRIs were sequentially chosen from OASIS and analyzed in MRIcron using two different visualization techniques: 1) skull-stripped surface renderings, and 2) serial sagittal slices. The AG was demarcated in the left and right hemisphere of each brain, as defined by the parallel and count-back methods. The reliability of each method for locating the AG was systematically assessed using both descriptive and inferential statistics, based on measures of hemispheric lateralityResults and discussionExamination of both methods for locating the AG showed poorer reliability in the left hemisphere compared to the right for both surface and more medial sites. Several anatomical factors were identified that compromised the reliability of the two methods.ConclusionsOur finding of poor reliability between the parallel and count-back methods suggests that the AG is sometimes difficult to identify, particularly in the left hemisphere. This places the traditional gross anatomical methods for locating the AG in question. Development of new techniques to define this area of human neuroanatomy is needed.

Auditory training (AT) is an important component of rehabilitation for patients with central auditory processing disorder (CAPD). The present article identifies and describes aspects of AT as they relate to applications in this population. A description of the types of auditory processes along with information on relevant AT protocols that can be used to address these specific deficits is included. Characteristics and principles of effective AT procedures also are detailed in light of research that reflects on their value. Finally, research investigating AT in populations who show CAPD or present with auditory complaints is reported. Although efficacy data in this area are still emerging, current findings support the use of AT for treatment of auditory difficulties.

To provide audiologists with strategies to minimise confounding cognitive and language processing variables and accurately diagnose central auditory processing disorder (CAPD).Tutorial.None.Strategies are reviewed to minimise confounding cognitive and language processing variables and accurately diagnose CAPD.Differential diagnosis is exceedingly important and can be quite challenging. Distinguishing between two or more conditions presenting with similar symptoms or attributes requires multidisciplinary, comprehensive assessment. To ensure appropriate interventions, the audiologist is a member of the multidisciplinary team responsible for determining whether there is an auditory component to other presenting deficits or whether one condition is responsible for the symptoms seen in another. Choice of tests should be guided both by the symptoms of the affected individual, as established in an in-depth interview and case history, the individual's age and primary language, and by the specific deficits reported to be associated with specific clinical presentations. Knowing which tests are available, their strengths and limitations, the processes assessed, task and response requirements, and the areas of the central auditory nervous system (CANS) to which each test is most sensitive provides the audiologist with critical information to assist in the differential diagnostic process.

Background: Temporal processing ability has been linked to speech understanding ability and older adults often complain of difficulty understanding speech in difficult listening situations. Temporal processing can be evaluated using gap detection procedures. There is some research showing that gap detection can be evaluated using an electrophysiological procedure. However, there is currently no research establishing gap detection threshold using the N1-P2 response. Purpose: The purposes of the current study were to 1) determine gap detection thresholds in younger and older normal-hearing adults using an electrophysiological measure, 2) compare the electrophysiological gap detection threshold and behavioral gap detection threshold within each group, and 3) investigate the effect of age on each gap detection measure. Design: This study utilized an older adult group and younger adult group to compare performance on an electrophysiological and behavioral gap detection procedure. Study Sample: The subjects in this study were 11 younger, normal-hearing adults (mean = 22 yrs) and 11 older, normal-hearing adults (mean = 64.36 yrs). Data Collection: All subjects completed an adaptive behavioral gap detection procedure in order to determine their behavioral gap detection threshold (BGDT). Subjects also completed an electrophysiologic gap detection procedure to determine their electrophysiologic gap detection threshold (EGDT). Results: Older adults demonstrated significantly larger gap detection thresholds than the younger adults. However, EGDT and BGDT were not significantly different in either group. The mean difference between EGDT and BGDT for all subjects was 0.43 msec. Conclusions: Older adults show poorer gap detection ability when compared to younger adults. However, this study shows that gap detection thresholds can be measured using evoked potential recordings and yield results similar to a behavioral measure.

Background: Auditory-evoked potentials (EPs) provide a more objective assessment of central auditory nervous system (CANS) dysfunction when compared to behavioral measures because they do not require a behavioral response (Anderson and Kraus, 2010). In this regard, the middle latency response (MLR) has been considered an important component of CANS assessment (Jerger et al, 1988); however, its large within-group variability limits its usefulness (Musiek et al, 1999). It has been argued that performing intratest calculations on the MLR (e.g., difference in EP amplitude when stimulating the left ear versus the right ear) can reduce the within-group variability of the MLR and enhance its clinical usefulness (Musiek et al, 1999; Weihing et al, 2012). To date, it has not been investigated how well these MLR intratest measures reduce within-group variability in adults of various ages, nor has it been shown that these intratest measures are sensitive to aging-related changes in the CANS. Purpose: The two primary goals of the present study were (1) to determine if calculating an intratest MLR measure, the difference in MLR Na-Pa peak-to-peak amplitude on left versus right ear stimulation (i.e., “ear effects”), will reduce within-group variability in adults of various ages; and (2) to determine if ear effect magnitude will change as a function of aging. Ear effects were measured in both quiet and in noise to determine if the addition of noise enhanced any age-related-effects. Research Design: A cross-sectional study was conducted. Study Sample: The researchers studied 30 adults ranging in age from 20–80 yr with hearing sensitivity of 25 dB HL or better at the octave frequencies from 500–2000 Hz, and no history of neurologic issues. Adults were assigned to one of three age groups based on their chronological age, which were young adults, middle-aged adults, and older adults. Data Collection and Analysis: MLRs were acquired using a Nicolet Spirit 2000 during a single laboratory visit. To determine if within-group variability decreased significantly with ear effects, variability for absolute amplitude measures was compared to ear effect variability using the Pitman t-test. To examine potential effects of background noise and aging, data were analyzed using a mixed-factorial analysis of variance with the within-subjects factor “background noise” and the between-subjects factor “age group.” Results: Within-group variability was significantly reduced by calculating ear effects for the youngest group only. Additionally, the oldest adults in the present sample showed significantly larger ear effects than younger and middle-aged adults. This effect did not appear to be a result of differences in peripheral hearing sensitivity. Finally, introducing noise into the paradigm did not influence the observed effects. Conclusions: Ear effects become larger in older adults possibly as a result of age-related changes in the subcortical and/or cortical generators of the MLR. Failure of the ear effect calculation to reduce within-group variability in the middle-aged and older adults suggests that interaural asymmetries in MLR amplitude become more variable across participants who are older than 50 yr. Information obtained from this measure may benefit the development of treatment plans for older adults with hearing difficulties.

Background: The role of the right temporal lobe in processing speech is not well understood. Although the left temporal lobe has long been recognized as critical for speech perception, there is growing evidence for right hemisphere involvement. To investigate whether the right temporal lobe is critical for auditory speech processing, we studied prospectively a normal-hearing patient who underwent consecutive right temporal lobe resections for treatment of medically intractable seizures. Purpose: To test the hypothesis that the right temporal lobe is critical for auditory speech processing. Research Design: We used a prospective, repeated-measure, single-case design. Auditory processing was evaluated using behavioral tests of speech recognition (words, sentences) under multiple listening conditions (e.g., quiet, background noise, etc.). Auditory processing of nonspeech sounds was measured by pitch pattern sequencing and environmental sound recognition tasks. Data Collection: Repeat behavioral testing was performed at four time points over a 2 yr period: before and after consecutive right temporal lobe resection surgeries. Results: Before surgery, the patient demonstrated normal speech recognition in quiet and under real-world listening conditions (background noise, filtered speech). After the initial right anterior temporal resection, speech recognition scores declined under adverse listening conditions, especially for the left ear, but remained largely within normal limits. Following resection of the right superior temporal gyrus 1 yr later, speech recognition in quiet and nonspeech sound processing (pitch patterns, environmental sounds) remained intact. However, speech recognition under adverse listening conditions was severely impaired. Conclusions: The right superior temporal gyrus appears to be critical for auditory processing of speech under real-world listening conditions.

Many individuals with central auditory nervous system (CANS) pathology/disorder report a variety of auditory symptoms with difficulty hearing in noise being one of the most common complaints (Chermak and Musiek, 1992) Interestingly, there seems to be a paucity of information in the literature on lateralized hearing loss symptoms in patients with central auditory disorders. Reported here is a case where the patient reported auditory symptoms, specifically hearing loss that was lateralized distinctly to the right ear. This ear was contralateral to a stroke that involved the left hemisphere with neural compromise limited primarily to the left Heschl's gyrus. Although the patient reported other hearing difficulties, the lateralized symptom of right-sided hearing loss seemed to be the most noticed. While the pure-tone audiogram was totally disassociated from the right ear auditory symptoms, central auditory tests revealed a marked and consistent right ear deficit, which was consistent with the site of lesion. It is rare that a relatively small lesion in Heschl's gyrus results in the perception of hearing loss so specifically localized to the right ear. It is also of interest that a patient with definite complaints of hearing loss would yield a normal, highly symmetrical pure-tone audiogram. The triad of patient symptoms, anatomy of the lesion, and central auditory test findings in this case are discussed, and theories as to possible underlying mechanisms for the patient's auditory deficits are provided.

Background: Normal temporal processing is important for the perception of speech in quiet and in difficult listening situations. Temporal resolution is commonly measured using a behavioral gap detection task, where the patient or subject must participate in the evaluation process. This is difficult to achieve with subjects who cannot reliably complete a behavioral test. However, recent research has investigated the use of evoked potential measures to evaluate gap detection. Purpose: The purpose of the current study was to record N1-P2 responses to gaps in broadband noise in normal hearing young adults. Comparisons were made of the N1 and P2 latencies, amplitudes, and morphology to different length gaps in noise in an effort to quantify the changing responses of the brain to these stimuli. It was the goal of this study to show that electrophysiological recordings can be used to evaluate temporal resolution and measure the influence of short and long gaps on the N1-P2 waveform. Research Design: This study used a repeated-measures design. All subjects completed a behavioral gap detection procedure to establish their behavioral gap detection threshold (BGDT). N1-P2 waveforms were recorded to the gap in a broadband noise. Gap durations were 20 msec, 2 msec above their BGDT, and 2 msec. These durations were chosen to represent a suprathreshold gap, a near-threshold gap, and a subthreshold gap. Study Sample: Fifteen normal-hearing young adult females were evaluated. Subjects were recruited from the local university community. Data Collection and Analysis: Latencies and amplitudes for N1 and P2 were compared across gap durations for all subjects using a repeated-measures analysis of variance. A qualitative description of responses was also included. Results: Most subjects did not display an N1-P2 response to a 2 msec gap, but all subjects had present clear evoked potential responses to 20 msec and 2+ msec gaps. Decreasing gap duration toward threshold resulted in decreasing waveform amplitude. However, N1 and P2 latencies remained stable as gap duration changed. Conclusions: N1-P2 waveforms can be elicited by gaps in noise in young normal-hearing adults. The responses are present as low as 2 msec above behavioral gap detection thresholds (BGDT). Gaps that are below BGDT do not generally evoke an electrophysiological response. These findings indicate that when a waveform is present, the gap duration is likely above their BGDT. Waveform amplitude is also a good index of gap detection, since amplitude decreases with decreasing gap duration. Future studies in this area will focus on various age groups and individuals with auditory disorders.

Objective: The ability to hear in background noise is related to the processing of the incoming acoustic signal in the peripheral auditory system as well as the central auditory nervous system (CANS). Electrophysiological tests have the ability to demonstrate the underlying neural integrity of the CANS, but to date a lack of literature exists demonstrating the effects of background noise on auditory cortical potentials. Therefore, the purpose of this investigation was to systematically investigate the effects of white noise on tone burst-evoked late auditory evoked potentials (N1, P2, and P3) in normal hearing young adults. Study Design: Twenty young-adult normal-hearing individuals served as subjects. A comparison of the late auditory evoked potentials (N1, P2, and P3) was made at multiple signal-to-noise ratios (SNRs) (quiet, + 20, + 10, 0). N1, P2, and P3 were elicited and both amplitude and latency were measured for each of the potentials. A standard oddball paradigm with binaural stimulation ...

Purpose To provide a commentary on “Auditory Processing Disorder and Auditory/Language Interventions: An Evidence-Based Systematic Review” by Fey et al. (2011). Method Examination of the conclusions drawn by Fey et al. (2011) in the context of the American Academy of Audiology (2010a, 2010b) and American Speech-Language-Hearing Association (2005a, 2005b, 2005c) guidelines for the diagnosis and treatment of auditory processing disorder, the evidence cited therein, and other pertinent published reports. Results The review provided by Fey et al. (2011) is limited due to the exclusion of pertinent efficacy studies from their analysis, inclusion of studies that did not employ strictly auditory-based therapies, and lack of well-defined experimental groups in many of the studies cited. Further, the questions posed by their literature review may not have addressed the efficacy of true auditory interventions in the remediation of auditory difficulties in children who have primary deficits in central auditory processing. Conclusion A more comprehensive review than that done by Fey et al. (2011) would have better addressed the fundamental question of the efficacy of direct remediation activities for children with central auditory processing disorder.

Background and Purpose— Auditory functional limitations experienced by patients after stroke of the central auditory pathways remain underinvestigated. Purpose— To measure patient-reported hearing difficulties in everyday life in nonaphasic patients with stroke of the auditory brain versus normal control subjects. To examine how hearing difficulties correlate with auditory tests and site of lesion in individual cases. Methods— We recruited 21 individuals with auditory brain stroke (excluding those with aphasia) diagnosed on the basis of a brain MRI conducted 1 to 2 weeks after the stroke and assessed in the chronic stage of stroke. Twenty-three controls matched for age and hearing were also recruited. All subjects completed the Amsterdam Inventory for Auditory Disability (consisting of subscales of sound detection, recognition, localization, speech in quiet, speech in noise) and underwent baseline audiometry and central auditory processing tests (dichotic digits, frequency and duration patterns, gaps in noise). Results— Sound recognition and localization subscores of the inventory were significantly worse in case subjects versus control subjects, with severe and significant functional limitation (z score >3) reported by 9 out of 21 case subjects. None of the inventory subscales correlated with audiometric thresholds, but localization and recognition subscales showed a moderate to strong correlation with dichotic digits (left ear) and pattern tests. Conclusions— A substantial proportion of patients may experience and report severe auditory functional limitations not limited to speech sounds after stroke of the auditory brain. A hearing questionnaire may help identify patients who require more extensive assessment to inform rehabilitation plans.

The present review summarizes historic and recent research which has investigated the role of the corpus callosum in dichotic processing within the context of audiology. Examination of performance by certain clinical groups, including split brain patients, multiple sclerosis cases, and other types of neurological lesions is included. Maturational, age related, and genetic factors are also discussed. Finally, some attention is given to recent trends in audiology research to develop improved diagnostic and rehabilitation tools for individuals with dichotic deficits potentially related to callosal dysfunction.

Purpose: The sensitivity, specificity, and efficiency of commonly used behavioral central auditory processing tests and test batteries were determined for 20 individuals with known lesions of the central auditory nervous system (CANS) and related auditory symptoms. Research Design: Twenty-nine individuals with no known neurological involvement served as the control group. Both groups were administered dichotic digits (DD), competing sentences (CS), frequency patterns (FP), and low-pass filtered speech (FS) tests. Data Analysis: Diagnostic indices for individual tests and test batteries comprised of two, three, or four tests were calculated both using a lax criterion in which failure on only one test in a battery led to a positive diagnosis and using a strict criterion in which failure on all tests in the battery was necessary to trigger a positive diagnosis. Results: The test battery providing the best balance between sensitivity and specificity varied as a function of criterion. The two-test DD-FP battery using a strict criterion demonstrated the best balance. Conclusions: Limitations of particular tests, the advantages of larger test batteries to more broadly examine multiple auditory processes, the degree to which the present results can be generalized clinically to populations without known brain lesions, and other clinical considerations are discussed.

The purpose of this study was to determine the middle latency response (MLR) characteristics (latency and amplitude) in children with (central) auditory processing disorder [(C)APD], categorized as such by their performance on the central auditory test battery, and the effects of these characteristics after auditory training. Thirty children with (C)APD, 8 to 14 years of age, were tested using the MLR-evoked potential. This group was then enrolled in an 8-week auditory training program and then retested at the completion of the program. A control group of 22 children without (C)APD, composed of relatives and acquaintances of those involved in the research, underwent the same testing at equal time intervals, but were not enrolled in the auditory training program. Before auditory training, MLR results for the (C)APD group exhibited lower C3-A1 and C3-A2 wave amplitudes in comparison to the control group [C3-A1, 0.84 microV (mean), 0.39 (SD--standard deviation) for the (C)APD group and 1.18 microV (mean), 0.65 (SD) for the control group; C3-A2, 0.69 microV (mean), 0.31 (SD) for the (C)APD group and 1.00 microV (mean), 0.46 (SD) for the control group]. After training, the MLR C3-A1 [1.59 microV (mean), 0.82 (SD)] and C3-A2 [1.24 microV (mean), 0.73 (SD)] wave amplitudes of the (C)APD group significantly increased, so that there was no longer a significant difference in MLR amplitude between (C)APD and control groups. These findings suggest progress in the use of electrophysiological measurements for the diagnosis and treatment of (C)APD.

Background: Use of a competition stimuli (e.g., video) in clinical settings is a widespread practice, yet the effects of these stimuli on evoked potentials are not well understood. Purpose: The present investigation acquired the click evoked auditory N1-P2 in quiet and in two types of competition: during presentation of an unrelated visual stimulus or audiovisual stimulus. Responses were acquired in each of these conditions at two click stimulus levels (i.e., 35 and 65 dBnHL) to determine if the effect of competition was greater closer to threshold. An attempt was made to quantify effect robustness by examining within- and between-session reliability. Research Design: Repeated measures ANOVA. Study Sample: 17 normal hearing female subjects. Results: Findings indicated a significant effect of audiovisual competition on the amplitude of the N1-P2, and a borderline significant effect of visual competition on this index. The extent of visual competition was better conveyed when examined on a case-by-case basis, in which was revealed a subgroup of the sample that was negatively affected by visual competition. There was no interaction between competition and click stimulus level. Conclusions: Although competition stimuli can negatively affect the amplitude of the N1-P2, consideration should be given to subjects on a case-by-case basis to warrant if removal of this stimulus is necessary.

Background: The middle latency response (MLR) can be a powerful tool for assessing integrity of cortical and subcortical auditory structures. Most research on the MLR, however, is constrained to relatively slow repetition rates by the time window necessary for response acquisition. Maximum length sequence (MLS) paradigms enable the recording of the MLR at high repetition rates, which could reduce test time and provide information about the behavior of auditory structures at rapid rates of stimulation. Purposes: To examine potential timing advantages and differences in waveforms between an MLS-MLR paradigm compared to a conventional MLR paradigm (Experiment 1), and to examine effects of rate on MLR morphology within the MLS paradigm (Experiment 2). Research Design: A repeated measures study. All subjects within each experiment underwent every condition for that experiment. Study Sample: Ten young adult female subjects participated in each experiment of this study. All subjects had normal hearing and negative neurological history. Data Collection and Analysis: Latency and amplitude values as well as the presence/absence of Na, Pa, Nb, and Pb components of the MLR were measured. Comparisons were made between the MLS-MLR and conventional MLR paradigms, as well as between repetition rates within the MLS-MLR paradigm. Results: Significant latency and amplitude differences were found between MLS and conventional MLR paradigms. The late components of the MLR (Nb, Pb) were present significantly more often when the MLS paradigm was used. No timing advantage was found with the MLS-MLR paradigm. Within the MLS paradigm, as repetition rate increases, latency becomes significantly shorter and amplitude significantly lower. Conclusions: Middle latency responses evoked by the MLS-MLR paradigm show significant differences from those evoked by a conventional MLR paradigm. The MLS-MLR paradigm can reliably evoke the late components (Nb, Pb) of the MLR and may be an important clinical tool for future investigation of these elements.

Background: The recently developed Gaps-In-Noise (GIN) test has provided a new diagnostic tool for the detection of temporal resolution deficits. Previous reports indicate that the GIN is a relatively sensitive tool for the diagnosis of central auditory processing disorder ([C]APD) in adult populations. Purpose: The purpose of the present study was to determine the feasibility of the GIN test in the pediatric population. Research Design: This was a prospective pseudorandomized investigation. Study Sample: This investigation involved administration of the GIN to 72 participants divided into six groups of normal children ranging from 7 through 18 years of age. Data Collection and Analysis: The approximate GIN threshold (the shortest gap duration for which at least four of six gaps were correctly identified) served as the dependent variable. Results were analyzed using an ANOVA to examine between- and within-group differences. Results: No statistically significant differences were seen in GIN thresholds among age groups. In addition, within group analysis yielded no statistically significant differences between ears within each age group. No developmental effect was seen in GIN thresholds between the ages of 7 and 18 years. Children as young as age 7 are able to complete the GIN with no significant difficulty and perform at levels commensurate with normal adults. The absence of ear differences suggests that temporal resolution as measured by the GIN is an auditory process that develops relatively early and symmetrically (i.e., no laterality or ear dominance effects). Conclusions: The GIN procedure appears to be a feasible measure of temporal resolution in both pediatric and adult populations.

Background: A common complaint of patients with (central) auditory processing disorder is difficulty understanding speech in noise. Because binaural hearing improves speech understanding in compromised listening situations, quantifying this ability in different levels of noise may yield a measure with high clinical utility. Purpose: To examine binaural enhancement (BE) and binaural interaction (BI) in different levels of noise for the auditory brainstem response (ABR) and middle latency response (MLR) in a normal hearing population. Research Design: An experimental study in which subjects were exposed to a repeated measures design. Study Sample: Fifteen normal hearing female adults served as subjects. Normal hearing was assessed by pure-tone audiometry and otoacoustic emissions. Intervention: All subjects were exposed to 0, 20, and 35 dB effective masking (EM) of white noise during monotic and diotic click stimulation. Data Collection and Analysis: ABR and MLR responses were simultaneously acquired. Peak amplitudes and latencies were recorded and compared across conditions using a repeated measures analysis of variance (ANOVA). Results: For BE, ABR results showed enhancement at 0 and 20 dB EM, but not at 35 dB EM. The MLR showed BE at all noise levels, but the degree of BE decreased with increasing noise level. For BI, both the ABR and MLR showed BI at all noise levels. However, the degree of BI again decreased with increasing noise level for the MLR. Conclusions: The results demonstrate the ability to measure BE simultaneously in the ABR and MLR in up to 20 dB of EM noise and BI in up to 35 dB EM of noise. Results also suggest that ABR neural generators may respond to noise differently than MLR generators.

The auditory steady state response (ASSR) has recently gained attention with respect to estimates of hearing sensitivity and configuration of hearing loss. The present investigation compared behavioral thresholds to estimated ASSR thresholds in subjects with confirmed CANS lesions to determine if this population can be accurately evaluated with ASSR techniques. Comparisons were made between the experimental group and a normal control group matched for age and hearing sensitivity. ASSR thresholds were obtained for the carrier frequencies of 500 and 2000 Hz with a 46 Hz modulation rate and compared to behavioral thresholds. Within and between group comparisons were made. The control group demonstrated strong correlation between their behavioral and estimated ASSR thresholds which significantly contrasted the neurological group. Additionally, individuals with neurological impairment of the CANS exhibited elevated thresholds that were on average 24 dB greater at 2000 Hz than their behavioral thresholds. These results suggest that individuals with neurological insult may appear as hearing impaired or having greater hearing loss than is actually present. As a result, the ASSR may demonstrate the potential to assist in the detection of CANS dysfunction. Las respuestas auditivas de estado estable (ASSR) han ganado atención recientemente con respecto a la estimación de la sensibilidad auditiva y la configuración de la pérdida auditiva. La presente investigación comparó los umbrales conductuales con umbrales estimados por ASSR en sujetos con lesiones CANS confirmadas para determinar si esta población podía ser evaluada con exactitud por medio de técnicas de ASSR. Las comparaciones se realizaron entre el grupo experimental y un grupo control normal ordenados por edad y sensibilidad auditiva. Los umbrales de los ASSR se obtuvieron por medio de frecuencias portadoras de 500 y 2000 Hz, con una tasa de modulación de 46 Hz y se compararon con los umbrales conductuales. Se realizaron comparaciones entre los grupos y dentro de un mismo grupo. El grupo de control mostró una fuerte correlación entre sus umbrales conductuales y los estimados por ASSR, que contrastó significativamente con el grupo neurológico. Adicionalmente, los individuos con un trastorno neurológico de CANS exhibieron umbrales elevados que fueron en promedio 24 dB más alto en 2000 Hz que sus umbrales conductuales. Estos resultados sugieren que los individuos con alteraciones neurológicas pueden lucir como alterados auditivamente o teniendo una pérdida auditiva mayor de la realidad. Como resultados, los ASSR puede demostrar el potencial para ayudar en la detección de la disfunción por CANS.

The corpus callosum consists of heavily myelinated fibres connecting the two hemispheres. Its caudal portion and splenium contain fibres that originate from the primary and second auditory cortices, and from other auditory responsive areas. The anterior commissure in humans is much smaller than the corpus callosum, and it also contains interhemispheric fibres from auditory responsive cortical areas. The corpus callosum is exclusively present in placental mammals, while in acallosal mammals, most of the corpus callosum-related functions are carried out by the anterior commissure. The exact contribution of these two structures and of interhemispheric transfer in hearing in humans is still a matter of debate. In more recent years, human behavioural studies which employ psychoacoustic tasks designed to tap into interhemispheric transfer, combined with sophisticated neuroimaging paradigms, have helped to interpret information from animal experiments and post-mortem studies. This review will summarize and discuss the available information of the contributions of the human interhemispheric pathway in hearing in humans from behavioural, neuroimaging and histopathological studies in humans.