Monita Chatterjee - US grants

Multi-channel cochlear implants have achieved phenomenal success in bringing the world of speech communication to the profoundly deaf. However, even the best implant users experience reduced speech intelligibility in the presence of background noise. This may turn an ordinary social activity such as dining at a restaurant, into a difficult endeavor. Our Hypothesis is that noise influences implant listening in two ways: first, it reduces the dynamic range and changes the loudness growth function and second, it changes the listeners; sensitivity to time-varying aspects of stimuli (such as modulation) Relatively little is known about the psychophysics of implant listening in noisy backgrounds. The overall long-term objective of this research is to achieve in-depth understanding of the effects of such backgrounds on the perception of simple and complex sounds in multi-electrode implant patients. Two fundamental aspects of electrical hearing are addressed in this proposal: 1. Limited dynamic range: Implant listeners have a very limited dynamic range from threshold to uncomfortable loudness level (ULL). We expect that a noise background will raise the threshold and lower the ULL of the tone ("recruitment"). However, the effect of the compressed dynamic range on the shape of the loudness function is unknown. Experiment 1 will measure loudness growth of both tones and AM signals in the presence of wideband, bandpass and lowpass filtered noise. 2.Sensitivity to amplitude modulations: As the degree of spectral detail available to implant listeners is particularly limited compared to normal hearing, sensitivity to temporal fluctuations may play an important role in the benefit derived from the implant. Experiment 2 will investigate the sensitivity of implant listeners to amplitude modulation in the presence of noise with different spectro-temporal characteristics. Experiments will be performed in users of both Nucleus and Clarion systems. For each experimental condition, different degrees of electrode separation between signal and noise will be used in order to address the issue of electrode- or channel- interaction, a third important factor in multi-electrode hearing. It is expected that this research will a) play a role in the development of future generations of auditory implant speech processors and b) provide insight into the fundamental mechanisms of auditory perception in noise.

DESCRIPTION (provided by applicant):Cochlear implant listeners today enjoy reasonably good speech understanding in quiet but generally experience severe deterioration in performance in the presence of background sounds. To provide usable speech information through the cochlear implant in the presence of competing sources (speech or nonspeech), basic principles underlying the perception of complex, multichannel stimuli by the electrically stimulated auditory system need to be investigated. This proposal aims to investigate mechanisms underlying complex pattern perception by cochlear implant listeners. The long-term goal of this research is to discover fundamental principles of complex stimulus perception by both electrically stimulated and normal hearing auditory systems. Two hypotheses will be investigated: a) that principles of perceptual organization can be used by cochlear implant listeners for separating out sounds from multiple sources and b) noise is important in signal processing by biological systems in general and by the auditory system in particular, and the right kind of noise introduced into cochlear implants will be beneficial. The proposed experiments are designed to measure the perceptual interactions between pulse-train carriers with similar / dissimilar temporal envelopes exciting adjacent / distant tonotopic locations. Methods will include detection and discrimination of complex stimuli, perceptual difference measures, and auditory streaming measures. Effects of noise on the detection of envelope cues in single- and multi-channel complex stimuli will be measured. It is expected that this research will yield fundamental insight into mechanisms of auditory perception with cochlear implants. Because of their fundamental nature, the findings are likely to also further our understanding of the normally functioning auditory system.

DESCRIPTION (provided by applicant): Cochlear implants (CIs) successfully deliver auditory information to the severely hearing impaired and the profoundly deaf. However, they do not succeed in noisy backgrounds, or in the presence of competing speakers. While research has shown that the brain can learn to adapt to adverse listening conditions using top-down processing, learning and top-down mechanisms can only help to a limited extent when the information transmitted to the auditory system is severely degraded. The long-term goal of our work is to uncover basic mechanisms underlying CI listeners'auditory sensitivity, and to relate these findings to their speech perception with the device. It is increasingly apparent that, to improve sound quality, speaker recognition, source segregation, and listening in noise, CIs will need to provide fine-grained information about the speech spectrum. It is unclear, however, to what extent CI listeners can process such information in a multi-channel stimulation context. Proposed experiments will quantify multi-channel spectral pattern recognition, multi-channel temporal pattern recognition, and multi-channel spectro-temporal interactions in CI listeners in the presence of competing, fluctuating maskers. Novel stimulation methods, such as current-steered virtual channel stimulation, will be explored, as will effects of more focused stimulation mode. Results will provide a view of the role of across-channel interactions in complex, dynamic electrical stimuli. In parallel, measures of phoneme recognition, gender recognition, and speech intonation recognition will be made, both in quiet and in competing noise. A comparison of these results to the results obtained from the psychophysical experiments will yield insight into those aspects of electrical stimulation that are critical for speech recognition in realistic listening situations. The results will not only yield important fundamental understanding of complex auditory processing by CI listeners, but they will also apply, in a broader sense, to auditory processing of complex stimuli by hearing-impaired and normal hearing listeners. The clinical relevance of the proposed work is that the findings will contribute to the development of clinical assessment tools and new speech processor designs for future auditory prostheses.

DESCRIPTION (provided by applicant): Natural variations in the pitch of spoken utterances convey important linguistic and emotional information to the listener. For children in particular, these prosodic cues are critical in the early stages of language learning. In tonal languages, the rapid changes in pitch carry lexical meaning. For young children, therefore, the ability to hear subtle differences in voice pitch is of great importance during the early years as they acquire their native language. Little, however, is known about children's sensitivity to subtle changes in voice pitch. Today, children who were born deaf or lost their hearing early in life routinely receive cochlear implants. Although cochlear implants facilitate the perception and acquisition of spoken language well, they are limited in the amount of voice pitch information that can be transmitted to the listener. It is, however, still possible that the early-implanted brain of young children, which is more adaptive than that of adults, may be able to overcome the limitations of the device to some extent. The goals of this project are to: i) measure the psychophysical sensitivity of school-aged normally hearing and cochlear-implanted children to changes in voice pitch; ii) quantify children's ability to process speech intonation and lexical tones using different acoustic cues when voice pitch is degraded; iii) quantify cochlear-implanted children's performance in similar tasks. The results of these studies will shed important new light on young children's sensitivity to voice pitch cues, how cochlear implantation might influence this sensitivity, and the extent to which the early-implanted auditory system can overcome an important limitation of the prosthesis.

DESCRIPTION (provided by applicant): Although cochlear implants provide a degraded version of the incoming sound to the listener, cochlear implantation early in life has helped thousands of children with severe hearing loss worldwide to interact verbally with their families, caregivers, teachers, and peers. This population is of great interest from a scientific viewpoint, as their auditory systems and their brains are developing with the device in place. Relatively little is known about the development of the brain under these conditions, particularly about the interaction of the degraded input to the system with the language acquisition system, the role of the neuroplasticity of the brain in the early years of life, and the factors that determine the relationship between the perception and production of sounds. Here, we focus on cochlear-implanted children's perception and production of voice pitch inflections in speech, which convey prosodic cues (question/statement contrasts, voice emotion) and word meaning (lexical tones in languages such as Chinese). A major problem in cochlear implants is that voice pitch information is poorly transmitted through the device. Yet, prosodic cues and emotional communication are critical for children's language acquisition and social development. For children learning a tonal language, the slower pitch changes convey prosodic/emotional information, while the more rapid inflections within syllables convey meaning, suggesting an even greater need for adequate pitch perception. In our previous work with adults, we have shown that listeners with cochlear implants as well as normal hearing place greater emphasis on secondary acoustic cues such as intensity changes when the primary cue is degraded. Here, we extend our work to ask how this compensatory skill develops in school-aged normally-hearing and cochlear-implanted children, and whether the shift in emphasis is also to be found in speech production by children with cochlear implants. We hypothesize that the perceptual sensitivity of children with cochlear implants to prosodic cues and lexical tones, as well as their ability to compensate by attending to secondary cues, will be determined by factors such as their age at implantation, age at onset of profound hearing loss, residual acoustic hearing, their ability to discriminate and identify dynamic pitch changes, the length of their experience with the device, and other factors such as their socio-economic status and nonverbal intelligence. We also hypothesize that the ability of children with cochlear implants to produce adequate pitch changes in their utterances, will be influenced both by their perceptual capabilities and their auditory history. Finally, we hypothesize that Mandarin-speaking children with cochlear implants will be better able to process dynamic voice pitch information than their English-speaking counterparts. The work, which will involve collaborations with labs in the US and Taiwan, is expected to have important implications for cochlear implant technology as well as rehabilitative therapies for children with cochlear implants.

DESCRIPTION (provided by applicant): Although cochlear implants provide a degraded version of the incoming sound to the listener, cochlear implantation early in life has helped thousands of children with severe hearing loss worldwide to interact verbally with their families, caregivers, teachers, and peers. This population is of great interest from a scientific viewpoint, as their auditory systems and their brains are developing with the device in place. Relatively little is known about the development of the brain under these conditions, particularly about the interaction of the degraded input to the system with the language acquisition system, the role of the neuroplasticity of the brain in the early years of life, and the factors that determine the relationship between the perception and production of sounds. Here, we focus on cochlear-implanted children's perception and production of voice pitch inflections in speech, which convey prosodic cues (question/statement contrasts, voice emotion) and word meaning (lexical tones in languages such as Chinese). A major problem in cochlear implants is that voice pitch information is poorly transmitted through the device. Yet, prosodic cues and emotional communication are critical for children's language acquisition and social development. For children learning a tonal language, the slower pitch changes convey prosodic/emotional information, while the more rapid inflections within syllables convey meaning, suggesting an even greater need for adequate pitch perception. In our previous work with adults, we have shown that listeners with cochlear implants as well as normal hearing place greater emphasis on secondary acoustic cues such as intensity changes when the primary cue is degraded. Here, we extend our work to ask how this compensatory skill develops in school-aged normally-hearing and cochlear-implanted children, and whether the shift in emphasis is also to be found in speech production by children with cochlear implants. We hypothesize that the perceptual sensitivity of children with cochlear implants to prosodic cues and lexical tones, as well as their ability to compensate by attending to secondary cues, will be determined by factors such as their age at implantation, age at onset of profound hearing loss, residual acoustic hearing, their ability to discriminate and identify dynamic pitch changes, the length of their experience with the device, and other factors such as their socio-economic status and nonverbal intelligence. We also hypothesize that the ability of children with cochlear implants to produce adequate pitch changes in their utterances, will be influenced both by their perceptual capabilities and their auditory history. Finally, we hypothesize that Mandarin-speaking children with cochlear implants will be better able to process dynamic voice pitch information than their English-speaking counterparts. The work, which will involve collaborations with labs in the US and Taiwan, is expected to have important implications for cochlear implant technology as well as rehabilitative therapies for children with cochlear implants.

PROJECT SUMMARY/ABSTRACT CORE B: TECHNOLOGY CORE The Technology Core (TC) is designed to provide computer programming, engineering, and data analysis support to all BTNRH investigators who conduct research related to perception and communication in children. It has been designed with five specific Aims, based on our experiences in Phase I. Aim 1 is to deliver innovative laboratory computing, engineering, and data acquisition support. Aim 2 is to provide expert guidance on statistical analyses and exploratory data analysis. Aim 3 is to develop cutting-edge software and instrumentation in the Auditory-Visual Core Facility. Aim 4 is to provide training for Project Leads, their staff and others. Aim 5 is to implement procedures to ensure long-term sustainability of the Technology Core. In Phase I, we initiated a process of providing unique and innovative solutions for the needs of Project Leads, which led to the development of several powerful software and hardware tools, including the completion of a state-of-the-art audio-visual research facility. In Phase II, we plan to continue such endeavors, taking into account the newly-expanded pool of research investigators at BTNRH, their needs and technical capabilities, while ensuring the future productivity of both the TC and the scientists it serves. To achieve these aims, the TC has been uniquely re-envisioned to include a cross-functional team of engineers as well as an experienced statistical consultant, incorporating efficient workflow design to ensure rapid responsiveness to investigators? needs, as well as resources to continue training and career-development for the TC team. The plan includes a formal process to ensure that the tools and software generated by the TC can be made available to investigators at BTNRH and shared by scientists at other institutions as well. The expanded, innovative capabilities of the TC will further enhance the rich scientific environment of the Center for Perception and Communication in Children.

PROJECT SUMMARY/ABSTRACT This application requests support for three postdoctoral positions in a multidisciplinary research training program in the area of human communication and its disorders at Boys Town National Research Hospital (BTNRH). The training program at BTNRH, currently in its 39th year, has provided postdoctoral training to a substantial number of highly qualified scientists who are presently working in the field of communication disorders. The purpose of the program is to fulfill two basic training needs: 1) advanced research training for applicants who are recent graduates of speech and hearing, communication sciences or language-related doctoral programs, and 2) training for applicants with a received doctorate in a related field of science, technology, engineering or mathematics who would benefit from additional research experience in a collaborative, research-intensive environment. The training program consists primarily of direct participation by trainees in behavioral and clinical translational research under the sponsorship of one or more experienced, independent scientists serving on the program faculty. Research at BTNRH is conducted in a wide range of disciplines and laboratories from clinical audiology to language development, with the focus on questions concerning the mechanisms underlying human communication and its disorders. The unique advantages of the BTNRH research environment for the training program include: 1) a faculty consisting of 16 behavioral, clinical and translational clinical scientists who serve as mentors; 2) a critical mass of research trainees, funded by a variety of mechanisms, including T32, F32, COBRE and R01 grants; 3) a clinical staff with access to a large and varied pediatric and adult patient population; 4) modern, well-equipped laboratories and diagnostic clinics; 5) a stimulating mix of areas of research across individual research laboratories; 6) access to support from software and hardware developers within BTNRH?s Technology Core; 7) access to support in human subject recruitment and standard clinical testing from BTNRHs? Human Subjects Core and 8) conditions that foster collaborative, multi-disciplinary research. Trainees are selected from PhD's, DSc's, and MD?s in areas relevant to ongoing research programs at BTNRH on the basis of their research capabilities and the likelihood of their interacting productively with training faculty. Particular attention is paid to identifying and inviting applications to the program from under- represented minority candidates and candidates with a disability. Every effort is made to enhance diversity in the postdoctoral training program and eventually in the group of scientists performing research related to the mission of the NIDCD.