The C1 and P1 (also called the P100) are two human scalp-recorded event-related brain potential (event-related potential (ERP)) components, collected by means of a technique called electroencephalography (EEG). The C1 is named so because it was the first component in a series of components found to respond to visual stimuli when it was first discovered. It can be a negative-going component (when using a mastoid reference point) or a positive going component with its peak normally observed in the 65–90 ms range post-stimulus onset. The P1 is called the P1 because it is the first positive-going component (when also using a mastoid reference point) and its peak is normally observed in around 100 ms. Both components are related to processing of visual stimuli and are under the category of pote