The many sound-generating sources within the environment produce an aggregate wave-form that enters the ear. In order to operate in, and make sense of the world, a listener has to be able to separate this input into source-related components, localize them, recognize them, and react appropriately. In this talk, I will discuss auditory perception and specifically what can be learned about perception by investigating how brain responses to sounds unfold over time. During the course of auditory processing, sensory information undergoes a transformation from a representation in purely physical terms to an abstract, behaviorally relevant form – two identical signals may be apprehended completely differently depending on the state of the perceiver. Since perception is inherently intimate and automatic, it is difficult to tap into its constructing stages. In my work, I employ simultaneous psychophysical and brain-imaging tools (Magnetoencephalography; MEG) to study the processes that underlie listener’s construction of a representation of the acoustic environment: the mechanisms by which auditory objects are detected and separated from background and the role of top-down processing such as attention. Specifically, I will talk about the temporal dynamics of the cortical systems that subserve the detection of auditory temporal edges. One particular outcome of this research is the discovery of a fundamental asymmetry in how transitions between order and disorder, or between signals with differing statistics, are processed in cortex. I will discuss what this asymmetry implies about processing and how it is related to listener’s ability to make sense of an ever changing, complex acoustic world.