Mark A. Bee - US grants

0107304
Bee
The International Research Fellow Awards Program enables U.S. scientists and engineers to conduct three to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.
This award will provide twenty-four months of support to Dr. Mark A. Bee to work with Dr. Georg M. Klump at the University of Oldenburg in Bremen, Germany on the mechanisms of auditory scene analysis in the European Starling.
The purpose of this research is to gain a greater understanding of the underlying neural mechanisms of auditory scene analysis, which is the organization of sounds into perceptual representations of the events that produced the sounds. The PI will study the neural basis of auditory scene analysis in the starling, a songbird that is an excellent model system of behavioral and neurobiological studies of auditory perception. He will use a methodological approach in which microelectrodes are chronically implanted into the starling's auditory cortex and neural responses to acoustic stimuli are recorded from awake, unrestrained birds via radiotelemetry. These experiments will identify areas of the auditory forebrain where different forms of auditory scene analysis occur and how these areas accomplish this complex task. The results will increase our understanding of the mechanisms of auditory scene analysis, contribute to a better understanding of human language acquisition and the evolution of hearing and potentially lead to the development of better hearing aids and voice-recognition-based computer-user interfaces.
Dr. Klump, formerly of the University of Technische Universitat Munchen, is a leading expert in the study of comparative audition and hearing in birds, and is the PI on a grant held by eight research groups in the Munich area focussing on the mechanisms of auditory scene analysis.

DESCRIPTION (provided by applicant): The broad aim of this research is to better understand the mechanisms of sound source perception. A critical aspect of perceiving distinct sound sources in multi-source environments is the auditory system's ability to separate sounds of interest from other overlapping sounds and background noise. Hearing aids and cochlear implants often provide their users little benefit when it comes to segregating multiple sound sources. Similarly, computer algorithms for automated speech recognition (ASR) also have persistent difficulty segregating multiple sources. A major goal of auditory neuroscience is to uncover the neural mechanisms that perform sound source segregation. A better understanding of these mechanisms, in turn, can lead to biologically-inspired improvements in hearing prosthetics and ASR algorithms. Though seldom stated explicitly in hearing research, the logic of this biomimetic approach is based on evolutionary thinking: the aim is to understand how natural selection has already solved problems of sound source segregation in living organisms. Naturally, most of this work is done using mammalian models because their auditory systems are most similar to those of humans. The project proposed here employs similar logic based on the premise that evolution is well known for finding diverse solutions to common problems in different animal lineages. The long-term goal of the proposed research is to increase knowledge about the mechanisms of sound source segregation by integrating perceptual and neurophysiological experiments in a lower vertebrate model (frogs) with a unique auditory system and an evolutionary history of solving difficult problems of source segregation. This project uses well-established methods to investigate how female tree frogs segregate the mating calls of individual males from the overlapping signals of other males and the general din of noise in a large breeding chorus. The problems that frogs encounter (and solve) when communicating in noisy social aggregations share many similarities with the human cocktail party problem. Three specific aims will investigate the spectral, temporal, and spatial cues that promote sound source segregation. Aim 1 (spatial release from masking) will investigate how the frog auditory system exploits spatial separation between signals and noise to achieve a release from auditory masking. Aim 2 (masking release in modulated noise) will investigate a form of masking release that depends on a listener's ability to exploit temporal fluctuations in background noise levels. Aim 3 (auditory stream segregation) will investigate the perceptual segregation of two overlapping calls. By investigating these aims in frogs, this project is expected to generate insights into the potential diversity of neural mechanism by which evolution has solved problems of source segregation. Hearing prosthetics and computer algorithms for automated speech recognition perform poorly in environments with multiple competing sound sources. A better understanding of how evolution has solved this type of sound source segregation problem in a diversity of animal models could lead to further biologically-inspired technological advances. Results from this study, and future related projects that will integrate behavior with neurophysiological methods, are expected to generate new and deeper insights into the neurosensory mechanisms of sound source segregation in a lower vertebrate model system that evolved to vocally communicate in noisy, multi-source environments.

Humans and other animals often communicate acoustically in noisy social environments. These environments present serious challenges to effective communication when multiple individuals signal simultaneously. A fundamental goal of auditory neuroscience is to understand how nervous systems group together the different sounds produced by one source in the presence of multiple competing sources. This research investigates auditory grouping in an animal model that communicates acoustically in large social groups and has a unique auditory system. The work uses behavioral assays and neural recordings to study how anurans (frogs and toads) use frequency cues to group the discrete sound elements comprising communication signals. Preliminary studies suggested that use of frequency cues by anurans is supported by two mechanisms, one similar to that of mammals and birds and one resulting from the unique physiology of anuran inner ears. Further study will investigate these mechanisms at various levels of the anuran auditory system. It is expected that low levels of the auditory system will use mechanisms similar to those that have been observed in other animals, but that there will be two distinct variations, again reflecting the anuran ears' unique physiology. At higher levels of the auditory system, a new mechanism is expected to manifest which combines frequency cues with temporal cues to produce a neural "readout" of the perceptual state of the animal. This research will contribute to a broader and more general understanding of how auditory systems perceive acoustic communication signals in noisy environments. Such data are essential for understanding the potential diversity of ways that evolution may solve common problems in diverse groups of animals. This basic biological knowledge, in turn, could one day benefit people with impaired hearing. The project also integrates research with the training and teaching of undergraduate and graduate students and additionally will foster an international collaboration.

Humans are not the only animals that recognize familiar individuals. In fact, many animals can recognize their social partners. However, we still know little about the sensory and learning processes by which animals come to recognize familiar individuals and how this behavior evolves. This project uses playback experiments in the wild to compare the processes by which frogs learn to recognize their neighbors. By comparing the behavior of two closely-related frog species that differ in this ability but share a recent evolutionary ancestor, the project will also test how recognition behavior evolved. This project will provide an international experience for undergraduate students, and create materials for both a course at the University of Minnesota and a public museum exhibit at Kaieteur National Park in Guyana.

Male Golden Rocket Frogs recognize and respond less aggressively to the calls of familiar territorial neighbors, while male Kai Rocket Frogs show no evidence of recognition. This project uses habituation-discrimination experiments with natural and synthetic calls to compare the perceptual basis of neighbor recognition in these two species. In the first experiment, the ability of males of both species to discriminate between the calls of different individuals will be examined to test the hypothesis that neighbor recognition evolves by narrowing the specificity of learned social categories. In the second experiment, synthetic calls, in which acoustic properties can be manipulated independently, will be used to test the hypothesis that male golden rocket frogs discriminate between the calls of different individuals using the most reliable acoustic cues of identity.