A type of EEG response, either generated in the primary sensory areas of the brain, initiated by a sensory stimulus, and called a sensory or exogenous potential, or generated elsewhere in the brain, initiated by cognitive activity, and called an event-related or endogenous potential. It is conventionally plotted as an amplitude change over time and symbolized by a letter followed by a number, thus the second positive evoked potential occurring 150 milliseconds after the initiating event is written either P2 (because it is the second positive potential) or P150. Also called an evoked response. See also average evoked potential, contingent negative variation, event-related potential, nerve conduction velocity, N140, N400, P50, P200, P300, readiness potential, string length. EP abbrev.