Signal detection theory describes how an observer makes decisions about weak, uncertain, or ambiguous events or signals. It is widely applied in psychology, medicine, and other related fields. This book describes the theory, explains its mathematical basis, and shows how to separate the observer's sensitivity to a signal from his or her tendency to say “yes” or “no.” Both detection of an event and discrimination between two events are treated. Chapters 1-4 describe the basic form of the signal-detection model and how to use it; Chapters 5-7 extend the model to different procedures such as identification of a signal; Chapters 8-10 expand it to other methods and distributions; and Chapter 11 describes the statistical treatment of detection data.