Little is known about the ability of mice to discriminate among the ultrasonic vocalizations they produce. The ability of six CBA/CaJ mice to discriminate among renditions of ultrasonic vocalizations within a defined category will be determined. A go/no go experimental method will be used to test the ability of these mice to discriminate among four ultrasonic vocalizations in each of four categories. The independent variable will be the combination of a background vocalization and a target vocalization, and the dependent variable will be measured as the percent correct discrimination. I predict that spectrotemporal dissimilarity among vocalizations will lead to better discrimination ability of the mice.