Sound Source Segregation

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.