 Abstract animals use hierarchical neural pathways to process sound, with different levels of the hierarchy specializing in different aspects of sound processing. Primary auditory cortex, A1, is responsible for detecting individual frequencies, while secondary auditory cortex, A2, is more sensitive to multiple frequencies simultaneously. A1 neurons are also able to distinguish between different sweeping directions of sound, while A2 neurons are better at combining multiple frequencies into one signal. Additionally, A2 neurons respond differently to different timing of two-tone signals, which suggests they may be able to process simultaneous sounds together. This article was authored by Amber M. Klein, Destiny A. Ponte, and Hiroyuki K. Kato.