Walsh & Hoyt: Visual-Evoked Potential

Until the early 1960s, the electroencephalogram (EEG) was the main technique available for clinical evaluation of electric activity of the human cortex. It was subsequently etermined that if the spontaneous occipital EEG was recorded while brief flashes of light were presented to an eye, changes would result in the occipital potential. These changes were called the visual-evoked potential, visualevoked response (VER), or the visual-evoked cortical potential (VECP). The VEP is simply a gross electric potential of the visual cortex in response to visual stimulation. Unlike the alpha rhythm that can be recorded from most regions of the cortex, the VEP is limited mainly to the occipital region of the brain. In addition, although the EEG contains signals with amplitudes generally between 20 and 100 microvolts and occasionally larger, the amplitude of VEP is between 1 and 20 microvolts.