These reflect brain activity generated by large populations of neurons acting synchronously and then volume conducting to the scalp surface, where the activity can be recorded non-invasively with small sensors or electrodes placed on the surface of the scalp. Following, for example the presentation of a visual stimulus on a computer monitor, positive- or negative-going deflections in the on-going EEG are referred to as ERP components and are thought to reflect distinct neural and mental operations in the processing of that stimulus or event. There are, for example, not only visually-evoked potentials (VEP), but also auditory-evoked potentials (AEP).
See Brain (neuro-) imaging, Contrast sensitivity, Electroencephalogram (EEG), Evoked activity (or responses), Mutual gaze, N170, Neuroimagiing studies, P400