Andrew J. Oxenham - US grants

This research aims to investigate the perceptual effects of compression in human auditory system. Fundamental to this aim is the development of a behavioral (psychoacoustic) measure of compression. Two alternative measures will be tested for this purpose, one using a variant of the pulsation threshold measure and the other using a nonsimultaneous masking task. First, the two measures will be tested with normal-hearing listeners using signal frequencies ranging from 500 Hz to 8 kHz over a wide range of signal levels. Next, the results from normal-hearing listeners will be compared with those from listeners with sensorineural hearing loss. Both sets of data will be validated by comparing them with relevant physiological data and with previous behavioral measures of auditory compression. It is hoped that a measure of residual compression in hearing-impaired listeners will allow the separation of transduction and active components of a given sensorineural hearing loss. The resulting estimates of compression from hearing-impaired listeners with hearing losses between 40 and 60 dB HL will be used to provide parameters for a recent model of loudness recruitment. The predictions of the model will then be compared on an individual basis with loudness matching data from the same hearing- impaired listeners. The individual estimates of auditory compression from the hearing-impaired listeners will also be used to provide predictions for other psychoacoustic tasks thought to be influenced by compression, namely the additivity of nonsimultaneous masking and the temporal decay of forward masking. These predictions will then be compared with data from the same listeners. The results should provide a deeper understanding of the changes in auditory perception caused by hearing loss. A reliable behavioral measure of auditory compression may also provide a useful clinical tool in the diagnosis of hearing impairment, and may assist in selecting the appropriate processing algorithms for digital hearing aids on an individual basis.

The purpose of this research is to investigate monaural auditory temporal processing new psychophysical data with quantitative model predictions. The project has three main aims: (i) To investigate the influence of peripheral (cochlear) non-linearities on psychophysical measures of temporal resolution; (ii) to examine the consequences of a loss of non-linearity due to sensorineural hearing loss; and (iii) to functionally characterize higher stages of temporal processing. Two experiments will examine the magnitude and the time course of psychophysical suppression to discover the extent of which physiological and psychophysical suppression are reflections of the same underlying process. The results will clarify the role of suppression in certain measures of temporal resolution. Further experiments will test the hypothesis that the non-linear growth of forward masking is a reflection of peripheral non-linearities and that more central processes can be treated as quasi linear. Results from normal-hearing listeners will be compared with those from listeners with moderate-to severe cochlear hearing loss to test whether the differences can be accounted for solely by the expected changes in peripheral compression. The hypothesis, if supported, will have important consequences for the modeling and understanding of temporal resolution in hearing-impaired listeners. The penultimate experiments will seek to elucidate the underlying mechanisms of forward masking comparing predictions of the two most popular theories, namely adaptation of response and persistence (or integration) of response, with experimental data designed to distinguish between the two. The final experiment will examine how information is combined across frequency in a forward-masking situation. An understanding of the changes in temporal resolution due to hearing impairment may ultimately assist in selecting appropriate parameters for the design of digital hearing aids.

DESCRIPTION (provided by applicant): The long-term goal of this project is to further our understanding of how the auditory system forms pitch percepts and how those percepts are used to separate sounds coming from different sources. The project has three main aims. The first aim is to use a combination of psychophysical experiments and quantitative modeling to investigate how pitch is coded in the normal and impaired human auditory system. Experiments will investigate the ability of normal-hearing (NH) and cochlearly hearing-impaired (HI) listeners to hear out, or resolve, individual harmonic components within a complex, and relate this to overall accuracy in pitch coding and to independent measures of frequency selectivity. It is hypothesized that the pitch produced by resolved harmonics is qualitatively different from that produced by unresolved harmonics alone and that HI listeners with poorer frequency selectivity may often have to rely on the latter, less accurate, form of pitch coding. The second aim is to use similar methods to test the limits of pitch perception in more complex situations. These experiments will test NH and HI listeners' ability to hear two pitches at once and to hear out one pitch in the presence of a competing hannonic sound. It may be that these abilities rely on the presence of at least some resolved harmonics; if so, HI listeners may often not be in a position to hear two pitches, or to hear out one in the presence of another. The third aim is to evaluate separately the influence of envelope and fine-structure coding (both of which are thought to play important but different roles in pitch perception) in our ability to perceptually separate different acoustic sources. This approach is more applied and attempts to quantify the information necessary to transmit speech in complex backgrounds, such as a competing talker or a fluctuating noise. The results may have significant implications for the design of cochlear-implant processors and for signal-processing algorithms for hearing aids.

DESCRIPTION (provided by applicant): Despite tremendous progress in cochlear implant (CI) technology and performance over the past three decades, speech perception through a CI remains considerably poorer than in normal hearing (NH), particularly in noisy backgrounds. Similar difficulties are experienced by hearing-impaired (HI) listeners, even after hearing-aid fitting. The long-term goal of this research is to improve auditory and speech perception via CIs and hearing aids, through a greater understanding of the basic mechanisms that contribute to, and limit, the perception of speech in challenging acoustic environments. The first aim studies auditory enhancement and context effects - similar to the negative afterimage and color constancy effects in vision. These effects may help normalize the incoming sound and produce perceptual invariance in the face of the widely varying acoustics produced by different rooms, different talkers, and different acoustic backgrounds. Little is known about these effects in either HI or CI listeners. If enhancement and context effects can be measured in CI users, the results will provide evidence against recent theories based on efferent control of cochlear gain. If HI and/or CI listeners do not exhibit enhancement effects, then our results will guide novel signal processing schemes that will recreate important aspects of perceptual normalization through signal processing. The second aim tests the hypothesis that spectral resolution helps segregate sounds with different spectral content, and that the usual measures of speech perception in spectrally matched noise underestimate the importance of spectral resolution in many real-world situations, where masking sounds are not usually matched to target sounds. We will then investigate the interaction between spectral resolution and time-dependent spectral gain changes based on the findings from Aim 1. The results should lead to the development of new clinical measures of speech perception that provide information regarding static and dynamic aspects of spectral resolution, and predict performance in everyday listening conditions. These measures will be used to guide and validate the new signal processing schemes developed under Aim 1. In the second part, we will test the hypothesis that the temporal envelope fluctuations inherent in steady noise play an important role in limiting speech perception of CI listeners. We will measure speech perception in noise and compare it to speech perception in broadband maskers that produce no amplitude fluctuations. A parametric study of the effect of different temporal amplitude modulation frequency bands on speech perception, in the absence of spurious inherent noise fluctuations will provide estimates in CI users of the relative contributions of different amplitude frequencies to speech masking. Overall, the proposed work will further our fundamental knowledge about dynamic aspects of spectral and temporal processing in normal, impaired, and electric hearing, and will lead to new approaches in signal processing that hold the promise of improving speech perception for hearing- impaired and CI listeners in complex and varying acoustic backgrounds.

DESCRIPTION (provided by applicant): Despite tremendous progress in cochlear implant (CI) technology and performance over the past three decades, speech perception through a CI remains considerably poorer than in normal hearing (NH), particularly in noisy backgrounds. Similar difficulties are experienced by hearing-impaired (HI) listeners, even after hearing-aid fitting. The long-term goal of this research is to improve auditory and speech perception via CIs and hearing aids, through a greater understanding of the basic mechanisms that contribute to, and limit, the perception of speech in challenging acoustic environments. The first aim studies auditory enhancement and context effects - similar to the negative afterimage and color constancy effects in vision. These effects may help normalize the incoming sound and produce perceptual invariance in the face of the widely varying acoustics produced by different rooms, different talkers, and different acoustic backgrounds. Little is known about these effects in either HI or CI listeners. If enhancement and context effects can be measured in CI users, the results will provide evidence against recent theories based on efferent control of cochlear gain. If HI and/or CI listeners do not exhibit enhancement effects, then our results will guide novel signal processing schemes that will recreate important aspects of perceptual normalization through signal processing. The second aim tests the hypothesis that spectral resolution helps segregate sounds with different spectral content, and that the usual measures of speech perception in spectrally matched noise underestimate the importance of spectral resolution in many real-world situations, where masking sounds are not usually matched to target sounds. We will then investigate the interaction between spectral resolution and time-dependent spectral gain changes based on the findings from Aim 1. The results should lead to the development of new clinical measures of speech perception that provide information regarding static and dynamic aspects of spectral resolution, and predict performance in everyday listening conditions. These measures will be used to guide and validate the new signal processing schemes developed under Aim 1. In the second part, we will test the hypothesis that the temporal envelope fluctuations inherent in steady noise play an important role in limiting speech perception of CI listeners. We will measure speech perception in noise and compare it to speech perception in broadband maskers that produce no amplitude fluctuations. A parametric study of the effect of different temporal amplitude modulation frequency bands on speech perception, in the absence of spurious inherent noise fluctuations will provide estimates in CI users of the relative contributions of different amplitude frequencies to speech masking. Overall, the proposed work will further our fundamental knowledge about dynamic aspects of spectral and temporal processing in normal, impaired, and electric hearing, and will lead to new approaches in signal processing that hold the promise of improving speech perception for hearing- impaired and CI listeners in complex and varying acoustic backgrounds.

The human senses provide the information to the brain about the world around us. Deficits in visual, auditory or other sensory inputs have a major impact on quality of life, including education, employment and social engagement, which in turn places a major burden on the US economy. The scale of this problem is large: According to reports by the World Health Organization (WHO) and the National Institutes of Health, there are approximately 5 million Americans with vision impairment and around 36 million Americans with some form of hearing loss. There is broad recognition of the need for interdisciplinary collaboration for translational research on disabilities. Research into the development of more effective assistive technologies and environmental modifications requires interdisciplinary expertise that unites a fundamental understanding of the basic sensory science (vision, audition, motor control, speech and language) with deep technical expertise in engineering, computer science, and other related fields. This National Science Foundation Research Traineeship (NRT) award to the University of Minnesota will enable the formation of an integrated and interdisciplinary training program in sensory science through the joint strengths of the university's Center for Cognitive Sciences and Center for Applied and Translational Sensory Science. The program's goal is to prepare future scientists to combine engineering approaches with scientific knowledge and methods so that they are in a position to develop the next generation of sensory aids that will improve the quality of life for Americans with sensory loss. The program will serve students from computer science, engineering, kinesiology, psychology, and speech-language-hearing disciplines through courses, research opportunities, internships in the medical-devices industry, and public outreach activities. A total of 49 different PhD students will be enrolled in the program over the course of the 5 years, 18 of whom will receive NRT fellowships.

This project creates a new interdisciplinary graduate training program that encompasses the following key aims: 1. Establish an academic program in the form of a graduate minor through which students will receive the focused, multi-disciplinary educational background they will need to address critical challenges in the development of assistive technologies for sensory loss. 2. Advance interdisciplinary research in translational sensory science through the development of structural mechanisms that support the formation of interdisciplinary research teams. 3. Provide extra-curricular training and networking opportunities to the trainees through supplementary mechanisms, including weekly journal clubs, summer and winter workshops, spring and fall research symposia, and an annual fall retreat. Students will also participate in public engagement such as preparation of podcasts on research topics of interest to the stakeholders. 4. Provide practical career development opportunities through personalized contacts with local and national companies. Many trainees will eventually seek employment in industry, and those who continue in academia should seek to engage in collaborative work with industry partners. In an effort to provide students with real-world experience that can inform their research and post-graduation career choices, the program will offer the trainees 8-10 week summer internship opportunities in industry-based applied research.

The NSF Research Traineeship (NRT) Program is designed to encourage the development and implementation of bold, new potentially transformative models for STEM graduate education training. The Traineeship Track is dedicated to effective training of STEM graduate students in high priority interdisciplinary research areas, through comprehensive traineeship models that are innovative, evidence-based, and aligned with changing workforce and research needs.

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.

Despite considerable progress in cochlear implant (CI) technology over the past three decades, speech perception via a CI remains considerably poorer than with normal hearing (NH), particularly in noisy backgrounds. Similar difficulties, although often to a lesser extent, are experienced by hearing-impaired (HI) listeners, whose hearing loss is not severe enough to warrant a CI, even after hearing-aid fitting. The long-term goal of this research is to improve auditory and speech perception via CIs and hearing aids, through a greater understanding of the basic mechanisms that contribute to, and limit, the perception of speech in challenging acoustic conditions. This goal is addressed through three specific aims. The first aim is to combine behavioral and non-invasive neural measures to better understand auditory context effects in NH, HI, and CI populations. Context effects are a crucial part of our perceptual experience, and help to maintain perceptual constancy ? the ability to recognize objects, voices, and words, in the face of different room acoustics, talker properties, and varying background noise. Little is known about how context effects are altered by aging, hearing loss, or CIs. The second aim is to study acoustic and linguistic context effects in speech, and to understand how age and hearing loss interact with this important class of context effects. The third aim is to understand the peripheral and more central contributions to individual differences in the outcomes of CI users. It is often assumed that peripheral and implant-related factors can explain a significant proportion of the variance in CI outcomes. This aim will provide a direct test of the assumption by comparing the variability among CI users with the estimated population variance among younger and older NH listeners under degraded listening conditions in both psychoacoustic and speech-based measures of performance, using larger samples than have been tested in the past. Overall, the results will provide new insights into the spectro-temporal processing of auditory and speech stimuli by NH, HI, and CI populations that will help in the treatment and rehabilitation strategies for people with hearing loss. Treatments include the incorporation of missing context effects that assist perception in varying acoustic conditions via signal processing in hearing aids and CIs, and rehabilitation may include training strategies that accelerate the ability of HI and CI patients to utilize linguistic context cues in everyday conversational environments.

ABSTRACT The proposed project will build and evaluate the safety and design needs of a new type of intracranial auditory prosthesis that targets the auditory nerve between the cochlea and the brainstem (auditory nerve implant, ANI) in order to substantially improve hearing performance over the current standard of care, the cochlear implant (CI). Current CIs provide crucial speech information to many recipients, but do not restore normal hearing, and are particularly challenged in noisy or complex acoustic environments. Despite concerted efforts over the past 25 years, little overall improvement in CI performance has been obtained, primarily due to the poor electrode- neural interface in which the CI electrodes are immersed in cochlear fluids and separated from the auditory nerve by the cochlea's bony wall. The new approach will build upon encouraging data from animal studies, well-established human surgical techniques to access the auditory nerve, and high-density electrode and safe stimulation technologies currently available for human use in order to test the safety and efficacy of the ANI that enables direct contact between the electrodes and the auditory nerve. The ANI provides great promise of improved speech and music perception for its prospective recipients, by overcoming the challenge that has limited improvements in CIs for the past quarter century. The first aim is to design and build a full ANI system in accordance with regulatory requirements, including necessary reliability, safety, functional, biocompatibility, and sterilization testing for human use. The ANI system will be built by combining a well-established CI device in the auditory implant field with a novel electrode and cabling technology already being evaluated in human patients for other clinical applications. The second aim is to refine the ANI surgery in human cadaver experiments and acutely during other relevant in vivo operations to consistently position and anchor the electrode array and cabling into the target region. The third aim is to develop and validate critical psychophysical tests to properly evaluate the performance of the ANI during the pilot human study, which can then inform the design of a future clinical ANI device. The fourth aim is to seek regulatory approvals and set up the clinical trial infrastructure and monitoring entities. The fifth and final aim is to perform a pilot ANI study in up to three deaf patients to obtain safety, reliability and functionality data that can properly guide the design of a proceeding clinical device and a feasibility study.

Project Summary The proposed ANI funded by the parent grant (1UG3NS107688-01) is a new central auditory prosthesis that targets the auditory nerve to substantially improve hearing performance (tonal range and resolution) over the current standard cochlear implant by interfacing directly with the auditory nerve. The funded parent grant supports the development and all necessary biocompatibility, safety and functional pre- clinical testing required to obtain an FDA Investigative Device Exemption (IDE) for the first in human demonstration in the UH3 part of the project. Since the start of the project in October 2018 it has become clear through discussions with the surgical team as part of the ongoing cadaver studies and a new FDA guidance on MRI compatibility for implantable devices, that a) having the ability to carry out an MRI in a human subject without the need to surgically remove the electrode would after all be highly desirable if not necessary, given the selected patient group(s) and b) that third party safety testing according to the new guidance is required to satisfy the need for highest possible safety for the study participants. These additional tasks were not anticipated or budgeted for in the original proposal. While the majority of regulatory, GMP and fabrication costs can be absorbed or are not affected by this additional task, the cost for the specific test devices and the third-party MRI testing provider would need to be added to the current budget through an administrative supplement. The third- party cost would be an overhead exempt pass through cost. The supplement project will evaluate potential safety hazards in patients with ANI devices for 1.5 and 3 T MRI systems through simulation and testing. This data will be provided to the FDA as part of the future IDE application and to BfArM for approval for use in the ANI clinical trial in Hannover, Germany. Based on a preliminary assessment, we anticipate that the generated data would support that the device can be considered conditionally MRI safe. If the full system is considered not MRI safe, then we can cut the cable and remove the stimulator module which only requires a superficial surgery and not the more invasive intracranial surgery to remove the electrode and assembly, assuming that the latter is passing the MRI safety testing. It will however stop the ability of patients to continue to participate in the study and to generate data. Only if the system and the electrode assembly are both considered MRI unsafe, would a full removal surgery be required. Beyond the specific need for this project, the supplement project will generate important safety, reliability and functionality data that can properly inform the design of a future clinical ANI devices and products at an early stage in the development cycle. The ability to allow MRI imaging in patients with chronic neuromodulation implants is seen as a critical potential barrier to widespread use.