Neural Coding of Signal Duration and Complex Acoustic Objects

Neurons selective for signal duration have been reported from the auditory midbrain and cortex in a variety of echolocating bats. The first part of this chapter discusses the importance of signal duration to echolocation by bats. It examines the different types of auditory duration-tuned neurons that have been described, explores the neural mechanisms that create their temporally selective response properties in the auditory midbrain or inferior colliculus, and ends by speculating on the possible function(s) of duration tuning to hearing and echolocation by bats. The second part of this chapter describes the neural representation of echoes of complex objects and species-specific vocalizations in the auditory cortex of echolocating bats. It highlights recent findings on how the coding of complex spectrotemporal echo features is related to important tasks in object recognition such as the normalization of object size or the processing of time-variant echoes from complex moving targets. To close the loop between neural processing mechanisms and perception, electrophysiological findings are related to the behavioral performance of bats in psychophysical tasks. The chapter concludes with a section on neural processing of conspecific vocalizations in the auditory cortex and amygdala of echolocating bats.