ABSTRACT
Among the more interesting brain responses are the “slow potentials” or “slow waves.” They are “slow” in the sense that they take longer to develop than do the sensory-evoked potentials and motor potentials discussed earlier. Two of these slow potentials are the contingent negative variation (CNV) and the readiness potential (RP), categorized by Vaughan (1969) as steady potential shifts. A third type of slow wave includes the components of the ERP that occur between 250 and 900 ms after the stimulus commonly referred to as P300. Some researchers prefer to call these later positive components P3 or P3b without imposing a particular latency on the responses. The term P300 is still commonly used because the original studies by Sutton and his associates (Sutton, Braren, & Zubin, 1965) found that the response peaked about 300 ms after some initiating stimulus. All of the slow waves mentioned thus far are endogenous in nature. This means they can be produced by internal (endogenous) processes and are less dependent on external (exogenous) stimuli than are the sensory or motor potentials previously described. These internal processes are among the more fascinating ones that can be studied by psychologists and include, among other attributes, intentions to move (readiness potential), expectancies regarding the occurrence of some stimulus (CNV), and decisions (P300). Because of their relation to cognitive events, many cognitive scientists have become interested in these slow waves, especially the P300. There are other large waves that can develop in the interval between 250 and 900 ms poststimulus. These include the previously discussed N400 wave indexing the size of the disparity between an expected and an actual stimulus, and the N350 and N550 waves that are unique to sleep.
