Gerald Kidd Jr. - US grants

The purpose of this project is to study how sensorineural hearing loss affects the ability of listeners to discriminate between complex sounds on the basis of spectral shape. The capability for distinguishing between complex auditory signals, including both speech and nonspeech sounds, is facilitated by a process known as "auditory profile analysis". According to preliminary theory, auditory profile analysis involves a spectral comparison or template matching between a given sound input and a reference stimulus stored in long-term memory. Frequency selectivity, stimulus uncertainty, auditory perceptual learning and short-term and long-term auditory memory appear to be important in auditory profile analysis. A two-interval forced-choice psychophysical measurement technique, in which each stimulus presentation level is chosen at random, allows the measurement of discriminability based solely on spectral shape. While the importance of auditory profile analysis in the discrimination of complex sounds is clear, virtually nothing is known about its actions in the presence of sensorineural hearing loss. The specific objectives of the present study are to refine the theory of auditory profile analysis through comparative measures between normally hearing and hearing-impaired listeners, and to advance the understanding of the perception of complex auditory stimuli in impaired listeners.

The purpose of the proposed study is to measure the ability of normally hearing and hearing-impaired listeners to discriminate between sounds on the basis of the shape or contour of the power spectra of the sounds. This capability, often called "auditory profile analysis," is thought to underlie the discrimination and identification of many types of sounds - including speech sounds. There have been many past studies of sound detection or discrimination in which the signal created a difference in spectral shape, even some studies purporting to study "spectral shape discrimination" as a separate form of auditory analysis. It has only been quite recently, however, that researchers have come to appreciate the extent to which the responses of observers in such studies may reflect simple comparisons of sound intensity rather than of the spectral pattern of the sounds and, conversely, the extent to which the judgments of listeners in many traditional detection tasks may reflect decisions about spectral shape. The separation of detection strategies based on differences in spectral shape from differences in overall intensity or the intensity within a single "critical band," is possible by a procedure first described by Spiegel, Picardi and Green (J. Acoust. Soc. Am., v70, 1981) in which the overall level of the sounds is randomized. In that procedure, the statistical properties limit performance based on differences in sound level. We propose a series of experiments which will measure the just- discriminable difference in spectral shape in normally hearing listeners and in listeners with sensorineural hearing impairment. In each of these experiments, the results will be analyzed with respect to the statistical constraints of the procedure, and, in some experiments to the capability of the individual listener to discriminate between sounds based solely on sound intensity. In addition, the experiments with, normally hearing listeners are designed to evaluate certain aspects of a model of some of the factors we believe are important in spectral shape discrimination.

The goal of this work is to gain better understanding of the role of central factors in auditory masking in listeners with sensorineural hearing loss. During the past two decades, the appreciation of the process of masking as consisting of both peripheral and central components has greatly increased due in large part to studies of "informational masking". Informational masking arises from stimulus uncertainty and involves cognitive factors such as focused attention and memory. Informational masking taps processes that may be important in everyday listening environments containing multiple sound sources and varying degrees of complexity. The purpose of this study is to extend the work on informational masking to listeners with hearing loss. This knowledge is critical because of the prevalence of auditory pathologies affecting the sensory mechanism and the extreme difficulty in communication such pathologies often cause, particularly in noisy listening conditions. Although it is clear that sensory pathology affects the spectral and temporal analysis performed at the periphery, there appears to be a significant component to masking that cannot be attributed purely to peripheral deficits. The plan is to test the hypothesis that some listeners with sensorineural hearing loss- especially those reporting extreme difficulty communicating in noise- experience large amounts of informational masking in certain conditions and make poor use of the cues that normally reduce informational masking. This hypothesis will be examined through a series of psychoacoustical experiments employing listeners with cochlear hearing loss. The goal is to correlate the amount of informational masking and ability to use cues to overcome informational masking with factors such as etiology and configuration of loss, age and speech recognition. A related goal is to better understand the conditions that normally cause informational masking and the cues or detection strategies that can reduce informational masking.

[unreadable] DESCRIPTION (provided by applicant): This application requests support to continue research aimed at understanding peripheral and central factors in auditory masking both in listeners with sensorineural hearing loss and in listeners with normal hearing. The specific aims include examining the role of perceptual and cognitive factors in auditory masking, determining the role of centrally-based "informational masking" in the communication difficulties experienced by listeners with hearing loss, and extending the theory of auditory masking to include informational masking. During the past award period, substantial progress was made in the understanding of informational masking - that is, masking that cannot be attributed to overlapping patterns of excitation. One important finding from recent work is that persons with sensorineural hearing loss appear to have great difficulty in segregating and attending to auditory "streams" in complex environments. This difficulty leads to increased informational masking and may be a significant part of the communication difficulties experienced by listeners with hearing loss. The proposed research plan is intended to further examine this finding and to extend the empirical and theoretical work on auditory masking. The empirical work consists of a series of human psychophysical and speech identification experiments in which signals or targets are masked by sounds having different proportions of peripherally-based "energetic masking" and centrally-based informational masking. A fundamental aspect of the research plan is to test the effectiveness of various cues that normally facilitate perceptual segregation of sounds. In addition, the usefulness of varying degrees of a priori information is examined. These experiments span a range of tasks from detection through discrimination to nonspeech and speech identification. We propose to test groups of listeners with sensorineural hearing loss, and matched groups of listeners with normal hearing, on a set of masking experiments that assess how hearing loss and task complexity interact. The theoretical work has several facets, including developing a better understanding of the mechanisms of masking and of modeling those mechanisms in both normal-hearing and hearing-impaired listeners. The ultimate goal of this work is to understand why people with hearing loss experience such great difficulty communicating in difficult situations like restaurants, parties, or other circumstances where there are many sounds at once and the listening situation is complex and uncertain. [unreadable] [unreadable] [unreadable]

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The Sound Field Laboratory (SFL) core provides infrastructure support for a wide range of acoustics and psychoacoustlcs studies supported by NIH/NIDCD and other funding agencies. The SFL was established through a joint effort by the Boston University Hearing Research Center and the College of Health and Rehabilitation Sciences at BU to provide a unique interdisciplinary acoustics research facility that would serve the auditory research community within Boston and surrounding areas. The SFL consists of several components: initially, a large sound-attenuating lAC booth was purchased and modified to permit varying degrees of sound reverberation to be produced in a controlled manner ranging from highly reflective to nearanechoic. In addition to the physical facility, technical expertise was provided to assist a range of users in designing and implementing studies in this unique space. Through support provided by past core center awards, the capabilities ofthe SFL have increased significantly and encompass a wide range of services to users both on site and off site including acoustic recording and analysis, software and hardware development and a variety of other scientific support services. As indicated by the record ofthe accomplishments of the various users, the SFL has served the research needs of many user groups both at Boston University and in the region generally and include several academic and other institutions. The purpose of the facility to foster collaborative and interdisciplinary research continues and has met with considerable success during the past periods of support. The overall goal is to provide support for a wide range of research projects in an efficient and cost effective manner by providing unique facilities, equipment and support services that avoid costly duplication of research capabilities and allow projects to be undertaken that would be too costly to conduct or literally would not be possible if the SFL support were not available.

DESCRIPTION (provided by applicant): In realistic, everyday acoustic environments human listeners - regardless of whether they have normal or impaired hearing - depend on the considerable processing power of the human brain to evaluate the auditory scene. The various sources of sound must be parsed, evaluated for relevance and significance, and then attention must be directed to the desired source (the target) while interfering sources (the maskers) are discarded and ignored. Listeners with sensorineural hearing loss (SNHL) - even when wearing hearing aids - often experience extreme difficulty perceptually navigating the auditory scene, severely limiting their ability to communicate effectively. From an acoustic perspective, the designation of a sound source as target versus masker is arbitrary because it depends on the current - and changeable - internal state of the observer. Although the amplification of sounds by hearing aids provides the best (often the only) option for improving communication for listeners with SNHL, current hearing aids inherently fail to solve the source selection problem because they amplify target and masker sounds indiscriminately. The challenge is to devise a hearing aid that focuses only on those sounds the listener chooses to attend and suppresses competing sounds, responding to the wishes of the listener immediately, accurately, and effectively. The goal of the work proposed here is to evaluate a new approach to providing amplification for listeners with hearing loss that is based on the premise that only the listener can make the distinction between which sources to attend and which to ignore. The experiments employ a prototype hearing aid that combines an eye-tracking device with an array of microphones that forms a steerable acoustic beam. By sensing where the eyes are focused, the prototype device can steer the beam of amplification toward the desired source. In that sense, it implements top-down control of focused amplification for the purpose of enhancing sound source selection. The primary goal is to determine the conditions under which top-down control of selective amplification, as implemented by this visually-guided hearing aid (VGHA), can benefit persons with SNHL in complex, dynamic and uncertain listening environments. This goal is to be accomplished under two specific aims that explore 1) hypotheses about top-down control of selective amplification in multitalker sound fields, and 2) the inherent dilemma posed by spatially selective amplification for simultaneously attending to a target source while concurrently monitoring the environment for new sources. A new approach to solving this dilemma will be examined using a dual task. The experimental plan to test these hypotheses employs listeners with hearing loss, matched listeners with normal hearing, and normal-hearing listeners under degraded stimulus conditions simulating the spatial hearing deficits caused by SNHL. Performance under VGHA conditions will be compared and contrasted to that obtained under representative control conditions, and the experimental plan is designed explicitly to take into account the type of masking - energetic versus informational - that is present.

This project will determine whether formal musical training is associated with enhanced neural processing and perception of sounds, including speech in noisy backgrounds. Music forms an important part of the lives of millions of people around the world, and it is one of the few universals shared by all known human cultures. Yet its utility and potential evolutionary advantages remain a mystery. This project will test the hypothesis that early musical exposure has benefits that extend beyond music to critical aspects of human communication, such as speech perception in noise. In addition, the investigators will test whether early musical training is associated with less severe effects of aging on the ability to understand speech in noisy backgrounds. Degraded ability to understand speech in noise is a common complaint among older listeners and hearing loss has been shown to be associated with social isolation and more rapid cognitive and health declines. If formal musical training is shown to affect improved perception and speech communication in later life, the outcomes could have a potentially major impact on quality of life,

Earlier studies have suggested relationships between early musical training and improved auditory neural processing and perception, but the studies' impact has been limited by small sample numbers and inconsistent methods between different studies. This project will test a large number of participants (N=360) with uniform recruitment criteria and testing protocols across six different sites. Measures will include the neural frequency following response (FFR) to speech sounds, behavioral frequency selectivity, speech perception in noise, speech perception against a background of competing talkers, pitch discrimination, and auditory masking. The participants will also complete other assessments, including a personality inventory questionnaire, a profile of musical perception skills, a spatial reasoning test to assess general cognitive ability, as well as a background questionnaire to determine socio-economic status, education, and musical background. Participants will be selected to span a wide range of ages and musical experience. The neural data and the speech perception measures will be related to factors of musical training, such as the number of years of musical training and the age at which musical training began. Scientific rigor will be assured by preregistering the study and the analyses and by making the data and analysis code publicly available via a dedicated website.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.