Using the psychological stress evaluator in conditions of extreme stress

The Psychological Stress Evaluator (PSEV) is a machine for detecting signs of stress in the voice. It was tested using tape recordings of negotiators during a prolonged terrorist siege in which a number of death threats were issued. The study aimed to test whether the PSEV could distinguish between the traces of terrorist voices before the death threats from voice traces at other points. A scoring system using the proportion of voice oscillations falling above defined amplitude levels was used. PSEV scores did rise significantly more just before the actual shooting of a hostage. Unfortunately, the apparatus proved to be slow and cumbersome in practice and of limited, or no, use during the course of incidents similar to the one analysed.