Psychophysiologists use noninvasive measures of physiological function to make inferences about psychological processes. They may also be interested in the way in which physiological systems provide support for, or imple ment, psychological processes. The chapters in this book represent a com prehensive set of examples of this approach involving a wide range of measures to study an equally wide range of psychological and physiological processes. Although there is a general interest in a variety of measures of autonomic nervous system (ANS) function, several investigators have also been concerned with measures of the somatic system and of the central nervous system (CNS). Furthermore, although many authors refer to the concepts of attention and orienting, there is considerable variation in the precise sense in which these concepts are used.