Using as a starting point the postulate that sensory systems have evolved to perform optimal transformations on behaviorally relevant or natural stimuli, we are using signal analysis methods and information theoretic principles to develop a theory of auditory processing. The purpose of our theory is not just to describe but to understand the neural representation of acoustic communication signals, including speech and music. First, we plan on analyzing the statistics of natural sounds and of speech, music and birdsong in particular. We propose to search for theoretical representations of sounds based on principles of statistical independence and sparse representation. Our derived representations will also attempt to maximize differences between acoustic features that meditate the qualitatively different acoustical percepts of rhythm, timbre and pitch. Second, we will test the validity of these theoretically derived representations in psychophysical experiments in humans, and behavioral experiments in songbirds. These experiments will test the effect on perception of systematically removing acoustic features along the particular dimensions that were derived in the statistical analysis. Third, we will develop information theoretic tools that will allow us to estimate the amount of redundancy in a neuronal ensemble response. These measures will be used to quantify how the neural representation changes as one ascends the auditory processing stream and to test whether the neural representation is becoming more sparse and independent as we theorized. Finally, we will record the neural responses in primary and secondary auditory areas in songbirds to playback of song and filtered song. The data from these neurophysiological experiments will be used to: 1) test the utility of the statistically derived representations to predict responses of single auditory neurons, 2) correlate neural responses and behavioral responses, 3) assess the nature of non-linearities in the response, and 4) test the assumptions of independence at the ensemble level. Our studies will give us insight on how speech, music and other complex sounds are processed by the auditory system. These studies could be instrumental in the development of novel methods for sound processing for hearing aids and auditory neural prosthetics, as well as diagnostic tools for classifying language and learning disorders.
The purpose of this research is to improve understanding of how the human brain represents complex sounds, speech and music in particular. This basic research has direct applications in bio-medical sciences in the development of better hearing aids or cochlear implants for better speech intelligibility and music appreciation. In the long term, the research might also help in understanding the cause of certain types of learning disabilities that involve poor speech comprehension or production.
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