We describe neurons in the auditory midbrain of an echolocating bat that process both the "where" and the "what" of acoustic signals. These two features are temporally segregated in the neural response of these neurons such that the initial component codes the "where" and the late component codes the "what" of a sound that the animal hears. The underlying mechanism is a short-duration binaural interaction occurring only during the initial component. The binaural interaction integrates information from both ears in order to code a sound's location. In contrast, the later component is a function of only one ear and hence is more concerned with detection or identification of the sound rather than its location. The temporal segregation of these response features becomes most apparent with short stimuli, such as bat echolocation calls. These stimuli recruit only the initial binaural interaction, and hence they primarily invoke localization processing. Pharmacological manipulations indicate that the binaural interaction occurs in the auditory midbrain, adding localization sensitivity to cells that would otherwise be insensitive to the "where" of the sound. The adaptive advantage for the animal is that this circuit significantly increases the number of neurons that participate in sound localization, thus increasing acuity for this task without sacrificing participation in other tasks.
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