A change in electrical activity of the brain in response to a stimulus, recorded as changes in voltage at the scalp surface. Current signal processing approaches allow averaging of EEG activity, and ERPs are extracted by the averaging of brain waves over several repetitions of stimulus items. ERPs have been useful to scientists as markers for specific processes in the brain. There are several types of ERPs: the N100, N200, P300, and N400, to name a few. The “N” and “P” designators are conventions for the polarity of the signal, negative and positive. The number denotes the latency after stimulus presentation, measured in milliseconds. The P300 has been reported to be a dependable indicator of concealed information, though its application to deception detection is not established. ERPs are generated by the central nervous system, and their use in deception tests is attractive because they are expected to be resistant to countermeasures.