Robert Wickesberg - US grants

Understanding how auditory information is processed in the cochlear complex is essential for developing diagnostic tools to evaluate the ascending auditory system and for determining what information must be provided by cochlear prosthesis. The cochlear nuclear complex is the first locus of auditory information processing after sound is transduced in the cochlea, and in the cochlear nuclei information carried by auditory nerve fibers is divided into parallel ascending pathways. A number of psychoacoustic experiments have pointed to the cochlear nuclei as the site of a process that reduces the information available for sound localization shortly after the onset of a sound and contributes to the precedence effect. In vitro studies have suggested that tuberculoventral neurons, which project from the dorsal (DCN) to the ventral cochlear nucleus (VCN), contribute to the reduction in information. Recently, in vivo findings showed that the tuberculoventral neurons mediate both a rapid and a slower inhibition. The rapid inhibition significantly decreased the response at the onset of a sound and the slower inhibition reduced the availability of information just after the onset. Although the rapid inhibition can suppress onset transients and the slower inhibition can contribute to the precedence effect, the precise functions of these two inhibitory inputs are unknown. Determining the functions of this intrinsic circuitry is central to understanding the processing of information in the ventral cochlear nucleus. The specific aims of this study are to determine how the rapid and the slower inhibitory inputs modulate the responses of VCN neurons to stimuli used in psychoacoustic studies on sound localization, to identify precisely the neural circuits that provide and control both the rapid and the slower inhibition, to characterize physiologically the tuberculoventral neurons, and to begin investigating the pharmacology that underlies the two changes in response. The specific aims will be accomplished using extracellular, single unit recordings in ketamine- anesthetized chinchillas. The recordings from VCN neurons will be made before and after injections of lidocaine are made at various locations and depths within the DCN to inactivate different components of the neural circuits projecting to the VCN. Tuberculoventral neurons will be identified by electrical stimulation of the tuberculoventral tract, and their responses to tones, clicks and noise will be characterized.

Arguably the most recalcitrant problem in speech perception has been identifying invariant aspects of the acoustic or neural signals that correspond to speech segments. This is an especially difficult problem because of the large variation in speech produced by different speakers. For decades it has been assumed that the main cues for speech recognition come from the most salient frequencies in our voices and how these frequencies change as we produce consonants and vowels. However, recent results using a form of speech that mimics what is heard by cochlear implant users have pointed to the primary importance of temporal cues, especially for the recognition of consonants. Temporal features in the responses of the auditory nerve have been identified after presentation of the American English stop consonants /d/, /t/, /p/ and /b/. For each of these stop consonants, the temporal features are unique, relatively invariant despite large acoustic differences in the speech sounds, and could, therefore, provide the temporal cues necessary for speech recognition. The present work extends this research to all American English consonants (including fricatives such as /f/) and nasals (such as /n/ and /m/) produced by many different speakers. The hypothesis is that for each consonant there are unique temporal patterns in the responses of the auditory nerve and these are unchanged by variations in the acoustics of speech. The proposed experiments will examine the representation of consonant-vowel syllables in the auditory nerve of chinchillas, which hear over the same frequency range as humans. Syllables produced by 12 talkers will be taken from a public corpus, and also synthesized using a noise vocoder (which mimics what cochlear implant patients hear). The responses of individual auditory nerve fibers to a syllable will be pooled to create an ensemble response. Dynamic time warping, which correlates highly with the psychoacoustic recognizability of a speech token, will provide a quantitative measure of similarity and difference between ensemble responses.

The study of temporal cues in ensemble responses is a new and fundamentally different approach to speech recognition which will provide important insights into how recognition is achieved despite acoustic variability. The results from these experiments will be necessary for developing better speech recognition algorithms, improving speech rehabilitation strategies and for enhancing speech coding in cochlear implants.

This Integrative Education and Research Traineeship (IGERT) project will educate a diverse cadre of neuroscientists and engineers at the University of Illinois with an advanced understanding of both neuroscience and engineering, enabling them to engage in both sophisticated collaboration and independent research across the traditional gap between these domains. Many of the most important and exciting scientific and technological challenges for the future are centered on neuroscience, the study of the brain. Many recent (and most future) advances in understanding the brain depend on engineering new technologies for sensing, imaging, and analyzing the brain and their innovative use by neuroscientists. Similarly, some of the greatest and most important technological challenges, such as creating neural prostheses for the disabled, require engineers with a profound understanding of neuroscience. IGERT students will thus carry out innovative interdisciplinary research on neuroscience areas of great scientific and engineering importance, such as speech and audition, brain and imaging, and neural implants that may lead to revolutionary advances in understanding the brain and in new technologies such as neural prostheses for the disabled. IGERT trainees will also receive training in leadership, communication skills, and the responsible conduct of research as well as preparation for academic or industrial careers. IGERT is an NSF-wide program intended to meet the challenges of educating U.S. Ph.D. scientists and engineers with the interdisciplinary background, deep knowledge in a chosen discipline, and the technical, professional, and personal skills needed for the career demands of the future. The program is intended to catalyze a cultural change in graduate education by establishing innovative new models for graduate education and training in a fertile environment for collaborative research that transcends traditional disciplinary boundaries.