P300 and the anticipation of information within an orienting response paradigm

Recent work on the P300 event-related potential (ERP) complex has suggested that it might be a component of the orienting response (OR). As earlier studies of the OR in other psychophysiological domains, such as that employing measurement of electrodermal activity, have suggested that it is sensitive to anticipated information processing demands, the present study was carried out to see whether P300s were also sensitive to anticipated information. P300s were measured in conditions in which the information in a stimulus was varied using a two-stimulus anticipation experiment - a warning stimulus (WS) informed subjects of the nature of an impending imperative stimulus (IS). The IS was a 100 msec duration exposure of a one- or six-letter matrix and subjects were required to report as many of these letters as they could detect. Both WS and IS were varied in terms of their informational content. The results showed that P300 amplitude to the WS varied according to the anticipated information processing requirements. It was concluded that P300 is an index of anticipatory activation - a process similar in function to that suggested by Sokolov's cognitive view of the, OR.