In real-world situations animals are exposed to multiple sound sources orig
inating from different locations. Most vertebrates have little difficulty i
n attending to selected sounds in the presence of distracters, even though
sounds may overlap in time and frequency. This chapter selectively reviews
behavioral and physiological data relevant to hearing in complex auditory e
nvironments. Behavioral data suggest that animals use spatial hearing and i
ntegrate information in spectral and temporal domains to determine sound so
urce identity. Additionally, attentional mechanisms help improve hearing pe
rformance when distracters are present. On the physiological side, although
little is known of where and how auditory objects are created in the brain
, studies show that neurons extract behaviorally important features in para
llel hierarchically arranged pathways. At the highest levels in the pathway
these features are often represented in the form of neural maps. Further,
it is now recognized that descending auditory pathways can modulate informa
tion processing in the ascending pathway, leading to improvements in signal
detectability and response selectivity, perhaps even mediating attention.
These issues and their relevance to hearing in real-world conditions are di
scussed with respect to several model systems for which both behavioral and
physiological data are available.