Surprise!… Surprise?

ABSTRACT The nature of the psychophysiological enterprise is examined as it bears on the study of the endogenous components of event‐related brain potentials (ERP). The view is taken that success in Psychophysiology should be measured by the degree to which psychophysiological data can be used in elucidating the processes that underly the behavioral product rather than by the enumeration of psychophysiological “correlates” of behavior. It is proposed that endogenous ERP components are best viewed as manifestations of the activities of “subroutines” invoked during the informational transactions of the brain. A theoretical account of an ERP component consists of the specification of the functional role of the subroutine it manifests. Studies of the P300 components are examined for the contribution they make to the development of such a theory of the P300. Experiments focusing on P300 latency and amplitude are reviewed and it is concluded that P300 may be a manifestation of the processes whereby schemas are revised. The relationship between P300 and the Orienting Reflex is discussed within the framework of this model. It is suggested that P300 amplitude may predict the memorability of events. A preliminary test of this prediction is described.