An event-related potential initially evoked by presenting a sequence of similar tones followed by an odd-ball tone. Interesting applications have been developed by a group of neurophysiologists in the American midwest.
Lie detection is traditionally done by measuring heart rate, skin conductance, and rate of breathing. These measures are sensitive to individual health issues. An example is the case of Los Alamos Laboratories, where federal investigators demanded that top nuclear physicists turn over lists of medication to polygraph operators.
The P300 event-related potential can be used to determine concealed knowledge that only a criminal would know. By placing details of the crime(s) randomly among a list of non-relevant items, one can distinguish criminal from citizen. If an individual recognizes a detail of the crime, they produce both a P300 event-related potential and are also guilty of, or at least familiar with, the crime.
A second application of P300 recognition waveforms is the diagnosis of Alzheimer's Disease. Dr. John Polich and several others have shown that as Alzheimer's progresses, P300 amplitude decreases and latency increases. While individual differences in neuromechanics prevent this from being a perfect diagnosis of the disease's progress, it can assist doctors in charting an individual's decline.