| The P300 component of the event related brain potential is thought to index our subjective interpretation of unexpected, relevant sensory events. It is thought to be a manifestation of neuronal activity during the modification of our neuronal model of reality, that which allows us to form expectancies for future events (Donchin, 1981). Despite all efforts, however, we still do not understand the functional significance of the P300. In particular, we do not know which neuronal processes give rise to this component, nor do we know which psychological process it reflects.;Two experiments are described which may support this view of the P300. The results suggest that the P300 may be a useful index of moment-to-moment changes in our expectancies, a feature which may allow us to predict an individual's response before it occurs. The relevance of these findings to the study of individual differences and personality are discussed.;In this paper, a theory of the functional significance of the P300 is presented. The P300 is described as the product of the inhibition of ongoing perceptual processes in posterior areas of the brain, to allow for the modification of the working neuronal model of reality, presumably through the activation of temporal-limbic structures. |
