High Quality Content by WIKIPEDIA articles! The P3b is a subcomponent of the P300, an event-related potential (ERP) component that can be observed in human scalp recordings of brain electrical activity. The P3b is a positive-going amplitude (usually relative to a reference behind the ear or the average of two such references) peaking at around 300ms, though the peak will vary in latency (delay between stimulus and response) from 250-500ms or later depending upon the task. Amplitudes are typically highest on the scalp over parietal brain areas.