Event-related potentials (ERPs) are physiological responses in the EEG which are time locked  to an ‘event’  (also called stimulus) which is frequently presented (typically 50-500 times) to a human subject and which requires some form of response and/or cognitive processing.  By studying ERP’s we can observe how the human brain processes information. The events or stimuli are usually presented in an audio or visual form and involve a task such as recognizing a (rare) target  stimulus within many (frequent) non-target stimuli. Each time the subject recognizes an event, a specific response is required, like pressing a button.

Equipment for measuring ERP