This research proposal aims to uncover how the auditory system codes rate as a feature of acoustic communication. Understanding human speech requires judgments based on rapid temporal intervals. A detailed consideration of how temporal processing detects linguistic contrasts will be important to understanding many disorders of language including dysphasia and dyslexia. Xenopus laevis provides a tractable model organism for this objective because of its rich repertoire of vocalizations that vary in the rate of repeated clicks. Tests of behavioral psychophysics will determine whether male clawed frogs categorically perceive the two female calls that differ only in click rate: one call signifies sexual receptivity of the female and stimulates male calling, whereas the other call functions as an antiaphrodisiac that suppresses male calling. Electrophysiological recording in the auditory midbrain and medulla will reveal whether cells are rate-tuned, and whether they form a spatial map of rate. Finally, neuroanatomical tracing will outline the construction of rate-sensitive auditory circuits and their influence on the control of vocal production.