Book excerpt: The polygraph, often portrayed as a magic mind-reading machine, is still controversial among experts, who continue heated debates about its validity as a lie-detecting device. As the nation takes a fresh look at ways to enhance its security, can the polygraph be considered a useful tool? The Polygraph and Lie Detection puts the polygraph itself to the test, reviewing and analyzing data about its use in criminal investigation, employment screening, and counter-intelligence. The book looks at: The theory of how the polygraph works and evidence about how deceptivenessâ€"and other psychological conditionsâ€"affect the physiological responses that the polygraph measures. Empirical evidence on the performance of the polygraph and the success of subjects' countermeasures. The actual use of the polygraph in the arena of national security, including its role in deterring threats to security. The book addresses the difficulties of measuring polygraph accuracy, the usefulness of the technique for aiding interrogation and for deterrence, and includes potential alternativesâ€"such as voice-stress analysis and brain measurement techniques.