Visually Evoked Potentials and Visual Perception in Man

When a bright light is flashed into the eyes of a subject whose electroencephalogram (EEG) is being recorded, it is often possible to see, riding the normal EEG record after each flash, a transient polyphasic potential change of several microvolts in amplitude. Until the advent of electronic computing aids it was difficult to separate such “Visual Evoked Potentials” (VEP’s) from the ongoing EEG activity, and they remained little more than a curiosity. The past decade, however, has seen a proliferation of relatively inexpensive electronic devices for the extraction and purification of repetitive signals corrupted by an uncorrelated background. In their simplest forms such devices rely on the averaging of successive samples, in this case of the EEG, for a limited period after each presentation of the stimulus (Goldstein, 1960); but with the help of more powerful statistical techniques it becomes possible to ask increasingly sophisticated questions about the form of these potentials and their relation both to the parameters of stimulation and to the processes of perception.