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Cortical analysis of complex acoustic environments


Shihab Shamma

Department of Electrical and Computer Engineering, University of Maryland, USA


Spectrotemporal modulations are critical in understanding the perception of complex sounds, especially in conveying intelligibility in speech and quality in music. Neurons in the primary auditory cortex extract and explicitly represent these modulations in their responses. In this talk, I shall review experimental methods to study the representation of these modulations in the cortex and the way they reveal the acoustic features of complex sounds. I shall also discuss various abstractions of this analysis to develop algorithms for the analysis of complex auditory scenes.

One example is the question of how spectrotemporal modulation content of speech can be used to assess its intelligibility, to discriminate it from non-speech signals, and to enhance it by performing Weiner-like filtering in the space of the cortical representation. In music, these modulations underlie the perception of sound quality, and hence can be effectively employed to construct a perceptually-meaningful metric of musical timbre.

Finally, I shall review recent extensions of these studies that explore the role of feedback and top-down attentional effects on the representation of modulations, measurements that are carried out while animals are engaged in a variety of auditory tasks. The resulting understanding of these rapid adaptive mechanisms has been formulated as algorithms for the segregation of complex sound mixtures to resolve difficult examples of the "cocktail-party problem".