Auditory scene analysis: Examining the role of nonlinguistic auditory processing in speech perception

From infancy we experience a complex auditory environment with acoustic information originating from several simultaneously active sources that often overlap in many acoustic parameters. Despite this confluence of sound we are able to hear distinct auditory objects and experience a coherent environment consisting of identifiable auditory events. Analysis of the auditory scene (Auditory Scene Analysis or ASA) involves the ability to integrate those sound inputs that belong together and segregate those that originate from different sound sources (Bregman, 1990). Accordingly, integration and segregation processes are two fundamental aspects of ASA. This chapter focuses on the interaction between these two important auditory processes in ASA when the sounds occur outside the focus of one's attention. A fundamental aspect of ASA is the ability to associate sequential sound elements that belong together (integration processes), allowing us to recognize a series of footsteps or to understand spoken speech. Auditory sensory memory plays a critical role in the ability to integrate sequential information. Think about how we understand spoken speech. Once each word is spoken, only the neural trace of the physical sound information remains. Auditory memory allows us to access the series of words that were spoken, and connect them to make meaning of the individual words as a unit. Transient auditory memory has been estimated to store information for a period of time at least 30 s (Cowan, 2001). In understanding how this memory operates in facilitating ASA, it is important to also understand the relationship between the segregation and integration processes. The question of how sequential sound elements are represented and stored in auditory memory can be explored using event-related brain potentials (ERPs).