Visual Evoked Potentials

Visual evoked potentials (VEPs) are described by O'Shea et al. (2009)[2]. They are caused by sensory stimulation of a subject's visual field and are observed using electroencephalography. Commonly used visual stimuli are flashing lights, or checkerboards on a video screen that flicker between black on white to white on black (invert contrast). The resulting waveform includes the C1 and P1 followed by the visual N1.

Visual evoked potentials are very useful in detecting blindness in patients that cannot communicate, such as babies or animals. If repeated stimulation of the visual field causes no changes in EEG potentials, then the subject's brain is probably not receiving any signals from his/her eyes. Other applications include the diagnosis of optic neuritis, which causes the signal to be delayed. Such a delay is also a classic finding in Multiple Sclerosis. Visual evoked potentials are furthermore used in the investigation of basic functions of visual perception. VEPs are also sometimes used to determine if someone is fraudulently alleging blindness.

The term "visual evoked potential" is used interchangeably with "visually evoked potential". It usually refers to responses recorded from the occipital cortex. Sometimes, the term "visual evoked cortical potential" (VECP) is used to distinguish the VEP from retinal or subcortical potentials.

The multifocal VEP is used to record separate responses for visual field locations.

Some specific VEPs are:

* Sweep visual evoked potential
* Binocular visual evoked potential
* Chromatic visual evoked potential
* Hemi-field visual evoked potential
* Flash visual evoked potential
* LED Goggle visual evoked potential
* Motion visual evoked potential
* Multifocal visual evoked potential
* Multi-channel visual evoked potential
* Multi-frequency visual evoked potential
* Stereo-elicited visual evoked potential