The auditory processing of complex signals is not yet fully understood making a clearer insight into auditory system processes worth aspiring to. One approach for this purpose is to gain a better understanding of the relations between physical parameters and hearing sensations by means of psychoacoustics. Suitable measures such as loudness help to characterize the perception of sound leading to more sophisticated loudness models which could be useful in optimizing hearing devices such as cochlear implants. The scope of this thesis therefore is the suprathreshold perception of sounds with different spectral, temporal and spatial content in normal-hearing listeners and cochlear implant users. Among others, this covers the applicability of categorical loudness scaling as a fast procedure to assess partial loudness as well as binaural and spatial hearing in cochlear implant users in a free-field measurement setup providing realistic spatial cues.
In natural environments, the auditory system is typically confronted with a mixture of sounds originating from different sound sources. As sounds spread over time, the auditory system has to continuously decompose competing sounds into distinct meaningful auditory objects or “auditory streams” referring to certain sound sources. This decomposition work, which was termed by Albert Bregman as “Auditory scene analysis” (ASA), involves two kinds of grouping to be done. Grouping based on simultaneous cues, such as harmonicity and on sequential cues, such as similarity in acoustic features over time. Understanding how the brain solves these tasks is a fundamental challenge facing auditory scientist. In recent years, the topic of ASA was broadly investigated in different fields of auditory research, including a wide range of methods, studies in different species, and modeling. Despite the advance in understanding ASA, it still proves to be a major challenge for auditory research. This includes verifying whether experimental findings are transferable to more realistic auditory scenes. A central approach in understanding ASA is the use of certain stimulus parameters that produce an ambiguous percept. The advantage of such an approach is that different perceptual organizations can be studied without varying physical stimulus parameters. Additionally, the perception of ambiguous stimuli can be volitionally controlled by intention or task. By using this one can mirror real hearing situations where listeners intent to identify and to localize auditory sources. Recently it was also found that in classical auditory streaming sequences perceptual ambiguity was not restricted to but was observed over a broad range of stimulus parameters. The proposed Research Topic pursues to bring together scientist in the different fields of auditory research whose work addresses the issue of perceptual ambiguity. Researchers were welcome to contribute experimental reports, computational modeling, and reviews that consider auditory ambiguity in its modality specific characteristics as well as in comparison to visual ambiguous figures. The overall goal of contributions was to consider the experimental findings from the perspective of real auditory scenes. In a broader sense, the Research Topic was open for contributions which are related to the issue of active listening in complex scenes.
Document abstract changed to 'The Lombard Effect (LE), defined as acoustic changes in speech production due to auditory feedback from the speaker's acoustic environment, has been shown to improve intelligibility in normal hearing and some hearing-impaired listeners. However, LE has not been investigated specifically for cochlear implant systems and users. For CI users, signal processing strategies generate an electric representation of the acoustic signal which has enabled high speech understanding performance in quiet conditions but declines in the presence of naturalistic noisy environments. In this thesis, a range of signal processing approaches are proposed to improve electric stimulation by influencing channel selection based on salient speech features and to leverage the acoustic properties of Lombard speech as a means to improve intelligibility for CI users in difficult listening scenarios. Traditional 'n'-of-'m' processing strategies utilize an energybased channel selection criteria to select 'n' out of 'm' available channels corresponding to the intracochlear electrode array. For speech-in-noise scenarios, noise-dominant channels may be selected at the expense of speech frequency-rich channels carrying important phonetic cues. For quiet listening scenarios, low-level consonant energy may be overshadowed by higher-level channels. To overcome these challenges, a formant-based channel selection scheme is used to determine the effect on channel selection and speech intelligibility. This approach is hypothesized to illicit minor yet strategic changes in the electric representation of speech to include formant frequency information in the presence of noise. Second, two apriori compression functions are proposed to increase the intensity of formants and consonant segments. Lastly, three proposed speech modification strategies inspired by Lombard speech are introduced. The ability of CI listeners to perceive LE, the benefits of LE perturbation of neutral input speech, and the effect of semantics on LE perturbation are all addressed. These perturbation approaches are hypothesized to illicit large, meaningful changes in the electric representation by altering the following changes in the speech structure: intensity, first formants and second formant location/amplitude/bandwidth, long-term average spectrum, fundamental frequency, and individual phoneme class duration. We demonstrate the implications of CI listeners to leverage salient features Lombard speech and examine the feasibility of Lombard perturbation to improve speech understanding for CI users.'
Millions of Americans experience some degree of hearing loss. The Social Security Administration (SSA) operates programs that provide cash disability benefits to people with permanent impairments like hearing loss, if they can show that their impairments meet stringent SSA criteria and their earnings are below an SSA threshold. The National Research Council convened an expert committee at the request of the SSA to study the issues related to disability determination for people with hearing loss. This volume is the product of that study. Hearing Loss: Determining Eligibility for Social Security Benefits reviews current knowledge about hearing loss and its measurement and treatment, and provides an evaluation of the strengths and weaknesses of the current processes and criteria. It recommends changes to strengthen the disability determination process and ensure its reliability and fairness. The book addresses criteria for selection of pure tone and speech tests, guidelines for test administration, testing of hearing in noise, special issues related to testing children, and the difficulty of predicting work capacity from clinical hearing test results. It should be useful to audiologists, otolaryngologists, disability advocates, and others who are concerned with people who have hearing loss.
The International Symposium on Hearing is a prestigious, triennial gathering where world-class scientists present and discuss the most recent advances in the field of human and animal hearing research. The 2015 edition will particularly focus on integrative approaches linking physiological, psychophysical and cognitive aspects of normal and impaired hearing. Like previous editions, the proceedings will contain about 50 chapters ranging from basic to applied research, and of interest to neuroscientists, psychologists, audiologists, engineers, otolaryngologists, and artificial intelligence researchers.
The Auditory System at the Cocktail Party is a rather whimsical title that points to the very serious challenge faced by listeners in most everyday environments: how to hear out sounds of interest amid a cacophony of competing sounds. The volume presents the mechanisms for bottom-up object formation and top-down object selection that the auditory system employs to meet that challenge. Ear and Brain Mechanisms for Parsing the Auditory Scene by John C. Middlebrooks and Jonathan Z. Simon Auditory Object Formation and Selection by Barbara Shinn-Cunningham, Virginia Best, and Adrian K. C. Lee Energetic Masking and Masking Release by John F. Culling and Michael A. Stone Informational Masking in Speech Recognition by Gerald Kidd, Jr. and H. Steven Colburn Modeling the Cocktail Party Problem by Mounya Elhilali Spatial Stream Segregation by John C. Middlebrooks Human Auditory Neuroscience and the Cocktail Party Problem by Jonathan Z. Simon Infants and Children at the Cocktail Party by Lynne Werner Older Adults at the Cocktail Party by M. Kathleen Pichora-Fuller, Claude Alain, and Bruce A. Schneider Hearing with Cochlear Implants and Hearing Aids in Complex Auditory Scenes by Ruth Y. Litovsky, Matthew J. Goupell, Sara M. Misurelli, and Alan Kan About the Editors: John C. Middlebrooks is a Professor in the Department of Otolaryngology at the University of California, Irvine, with affiliate appointments in the Department of Neurobiology and Behavior, the Department of Cognitive Sciences, and the Department of Biomedical Engineering. Jonathan Z. Simon is a Professor at the University of Maryland, College Park, with joint appointments in the Department of Electrical and Computer Engineering, the Department of Biology, and the Institute for Systems Research. Arthur N. Popper is Professor Emeritus and Research Professor in the Department of Biology at the University of Maryland, College Park. Richard R. Fay is Distinguished Research Professor of Psychology at Loyola University, Chicago. About the Series: The Springer Handbook of Auditory Research presents a series of synthetic reviews of fundamental topics dealing with auditory systems. Each volume is independent and authoritative; taken as a set, this series is the definitive resource in the field.
In suboptimal listening environments when noise hinders the continuity of the speech, the normal auditory-cognitive system perceptually integrates available speech information and & ldquo;fills in & rdquo; missing information with help from higher level feedback mechanisms. However, individuals with cochlear implants (CIs) find it difficult and effortful to understand interrupted speech compared to their normal hearing (NH) counterparts. Little is known about CI listeners & rsquo; ability to restore missing speech when they are exposed to challenging listening environments. In this dissertation, three experimental paradigms were used to evaluate listeners & rsquo; ability to utilize their acquired linguistic skills in normal hearing individuals using simulated cochlear implant processing and in individuals with cochlear implants. In the first experiment, listeners & rsquo; abilities to use semantic context when speech was intact or interrupted was evaluated under various spectral resolution conditions. The results suggested that higher level processing facilitates speech perception up to a point but it fails to facilitate speech understanding when speech signals are significantly degraded. In the second experiment, high level processing was investigated using the phonemic restoration effect where sentences were interrupted with and without filler noise at different interruption rates. Both groups failed to show top-down restoration, except the CI users showed some amount of higher level processing at the lowest interruption rate. In the third experiment, a gated word recognition task was used and listeners with CIs required comparatively more acoustic-phonetic information to recognize a word than the NH listeners. In the final experiment, when speech was presented in noise, both groups relied significantly on contextual cues to perceive the speech. Overall, the results from successive experiments indicated CI users rely heavily on contextual cues when they are available. However, when they listen to speech with severe degradations, they may not benefit from semantic context as the incoming speech does not provide enough information to trigger top-down processes. If the signal fidelity (spectral resolution) is improved, their benefit from higher level linguistic feedback processes can be maximized.
Volume 1: The Ear (edited by Paul Fuchs) Volume 2: The Auditory Brain (edited by Alan Palmer and Adrian Rees) Volume 3: Hearing (edited by Chris Plack) Auditory science is one of the fastest growing areas of biomedical research. There are now around 10,000 researchers in auditory science, and ten times that number working in allied professions. This growth is attributable to several major developments: Research on the inner ear has shown that elaborate systems of mechanical, transduction and neural processes serve to improve sensitivity, sharpen frequency tuning, and modulate response of the ear to sound. Most recently, the molecular machinery underlying these phenomena has been explored and described in detail. The development, maintenance, and repair of the ear are also subjects of contemporary interest at the molecular level, as is the genetics of hearing disorders due to cochlear malfunctions.
Spoken word recognition often involves the integration of both auditory and visual speech cues. The addition of visual cues is particularly useful for individuals with hearing loss and cochlear implants (CIs), as the auditory signal they perceive is degraded compared to individuals with normal hearing (NH). CI users generally benefit more from visual cues than NH perceivers; however, the underlying neural mechanisms affording them this benefit are not well-understood. The current study sought to identify the neural mechanisms active during auditory-only and audiovisual speech processing in CI users and determine how they differ from NH perceivers. Postlingually deaf experienced CI users and age-matched NH adults completed syllable and word recognition tasks during EEG recording, and the neural data was analyzed for differences in event-related potentials and neural oscillations. The results showed that during phonemic processing in the syllable task, CI users have stronger AV integration, shifting processing away from primary auditory cortex and weighting the visual signal more strongly. During whole-word processing in the word task, early acoustic processing is preserved and similar to NH perceivers, but again displaying robust AV integration. Lipreading ability also predicted suppression of early auditory processing across both CI and NH participants, suggesting that while some neural reorganization may have occurred in CI recipients to improve multisensory integrative processing, visual speech ability leads to reduced sensory processing in primary auditory cortex regardless of hearing status. Findings further support behavioral evidence for strong AV integration in CI users and the critical role of vision in improving speech perception.
Complex broadband sounds are decomposed by the auditory filters into a series of relatively narrowband signals, each of which conveys information about the sound by time-varying features. The slow changes in the overall amplitude constitute envelope, while the more rapid events, such as zero crossings, constitute temporal fine structure (TFS). Although envelope cues from a small number of channels can support robust speech recognition in quiet, TFS seems to plays a significant role for speech perception in noise, especially in fluctuating background. Fundamental questions about the relative importance of envelope and TFS have been addressed by many studies. The definition of TFS poses a critical issue. Due to the coupling between envelope and phase, it is problematic to isolate the TFS from the envelope for any signal which is not extremely narrowband. Conventionally, a Hilbert transform is used to represent each band as the product of the Hilbert envelope and a frequency-modulated (FM) sinusoidal carrier. The FM component is then taken as the TFS of the band. We show in this dissertation that the Hilbert FM is a distorted representation. To address this concern, we proposed a new distortion-free additive view of signal decomposition, the slow envelope and the fast envelope, using half wave rectification followed by filters reflecting engineering interpretation of neural physiology. The slow envelope is a tool for representing temporal cues that can be coded in the average firing rate of auditory nerve fibers, while the fast envelope instead captures the temporal cues conveyed in neural phase locking patterns. Using this new decomposition and the conventional Hilbert decomposition, we investigated the relative contribution of neural envelope and TFS coding to speech intelligibility in different noise conditions. The neural representation was generated by a simplified peripheral auditory model (Shamma and Lorenzi, 2013). We observed that the distortions in the Hilbert FM likely confounded the importance of TFS and made it seem insignificant. In contrast, the trends observed with fast envelope were in line with previous perception studies, suggesting that TFS plays a significant role in masking release. Due to the inherently coarse spectral and temporal resolution in electric hearing, conventional cochlear implant (CI) coding strategies only transmit envelope cues in a small number of channels. The lack of TFS potentially contributes to CI users' difficulties in understanding speech in noise and perceiving music. To encode fine structure information for CI users, we proposed a harmonic-single-sideband-encoder (HSSE) strategy that explicitly tracks the harmonics in complex sounds and transforms them into modulators conveying both envelope and TFS cues. A key distinction about HSSE is that it keeps the envelope and TFS cues together during the transformation to avoid distortions. The effectiveness of HSSE to speech and music perception were tested using three approaches, including acoustic simulation in normal hearing listeners, neural response simulation using a population auditory nerve model (Imennov and Rubinstein, 2009), and acute test in CI patients. Significant effects of HSSE on speech perception in noise and music perception were observed, which illustrated the potentially large benefit of providing fine structure information in a cochlear implant.
