(Medical Xpress) — In both animals and humans, vocal signals used for communication contain a wide array of different sounds that are determined by the vibrational frequencies of vocal cords. For example, the pitch of someone’s voice, and how it changes as they are speaking, depends on a complex series of varying frequencies. Knowing how the brain sorts out these different frequencies—which are called frequency-modulated (FM) sweeps—is believed to be essential to understanding many hearing-related behaviors, like speech. Now, a pair of biologists at the California Institute of Technology (Caltech) has identified how and where the brain processes this type of sound signal.