State the series of stimuli
ERPs a series of stimuli such as tones or light flashes are presented to the participant, and the raw EEG for a precise one or two second period following each stimulus is recorded and fed into a computer where it is summed and averaged. This will be a response (or 'event-related potential') in the brain to each separate stimulus but this will be small (millionths of a volt) in comparison with the background EEG (thousandths of a volt). By summing all EEGs together and averaging them, the more-or-less random EEG averages to zero, to leave an ERP that has a characteristic waveform when shown on the computer screen. Various abnormalities in this waveform have been linked to predisposition to alcoholism and schizophrenia. The ERP technique has also been useful as a tool to explore the mechanism of attention