Auditory looming perception in rhesus monkeys.

The detection of approaching objects can be crucial to the survival of an organism. The perception of looming has been studied extensively in the visual system, but remains largely unexplored in audition. Here we show a behavioral bias in rhesus monkeys orienting to "looming" sounds. As in humans, the bias occurred for harmonic tones (which can reliably indicate single sources), but not for broadband noise. These response biases to looming sounds are consistent with an evolved neural mechanism that processes approaching objects with priority.