during development plays a particular important role in shaping the auditory circuitry.t
Environmental sounds and animal vocalizations mostly occupy a subset of all physically plausible sounds.  In this subset, natural sounds can be categorized into three coarse functional groups: noisy, tonal, and click-like sounds; the nature of the sound being a direct consequence of the physical properties of the sound emitter.  In speech signals, by combining voiced and unvoiced sounds, and, fast and slower lip and tongue motions, humans make use of these three sound types.  In addition, the natural environment affects the propagation of sounds causing specific alterations and degradations. The combination of the properties of the sound emitter and effects of the environment determine what we call the statistics of natural sounds.  These statistics also determine the sound features that can carry information in communication signals. 
Perception of sound identification is organized along three major percepts: rhythm, pitch and timbre.  We believe that the nature of these distinct percepts is closely related to the statistics of natural sounds;  these acoustical perceptual dimensions encode information bearing features in sound that are invariant across sound sources or particular environmental degradations.  For example, the pitch of a note and the resulting melody when notes are strung together are constant across musical instruments or human or animal singers.  Similarly, differential frequency attenuation as sound travels long distances or particular frequency masking from other sources will have a relatively minor effect on the rhythmic qualities of the sound.   
The auditory system that mediates these percepts must therefore be sensitive to particular classes of sound features that are organized along dimensions that are closely related to the major perceptual dimensions and the dimensions that characterize the statistics of natural sounds.   Such a neural representation must be the result of computations along the auditory processing stream because it is absent at the auditory periphery where the sound pressure waveform is decomposed into frequency channels by the inner ear.  This decomposition results in an efficient representation for transmitting a reliable copy of the sound pressure waveform but, by itself, does not provide any of the synthesis required for extracting the information bearing features in the complex sounds.
The major hypotheses that we are investigating can therefore be framed around a central idea:  the three separate dimensional spaces characterizing the statistics of natural sounds, the major auditory perceptual features and the neural representation at the higher levels in the auditory system are related in the strong sense of being similar and interdependent.  This central idea lead us to the following more specific hypotheses : i) the role of the auditory computations is to extract information bearing features in natural sounds; ii) these information bearing features are organized along major acoustical percepts;  iii) the information bearing features and the corresponding percepts correspond to invariant characteristics of natural sounds.  In addition, we are interested in investigating the ontogeny of the auditory representations.  We believe that, to a large extent, the higher level representations of sounds are learned and that experience during development plays a particular important role in shaping the auditory circuitry.