SSVEP

Steady-state visual evoked potentials, or SSVEPs, are a type of electroencephalography (EEG) signal elicited by repetitive visual stimuli. When a person views a flickering visual stimulus at a constant frequency, their brain activity, particularly in the visual cortex, synchronizes with this flickering frequency. This synchronized brain response is the SSVEP.

The SSVEP is measured by placing electrodes on the scalp, typically over the occipital region where the visual cortex is located. The amplitude and phase of the recorded EEG signal at the stimulus frequency and its harmonics are analyzed to detect and quantify the SSVEP. The strength of the SSVEP is generally proportional to the stimulus intensity and the attention paid to the stimulus.

SSVEPs have found applications in various fields, most notably in brain-computer interfaces (BCIs). In BCIs, users can control external devices by focusing their attention on different flickering visual targets. Each target flickers at a unique frequency, and the BCI system detects which target the user is looking at by identifying the corresponding SSVEP frequency in their brain activity. This allows for non-invasive control of computers, wheelchairs, and other assistive technologies.

Beyond BCIs, SSVEPs are also used in research to study visual attention, visual perception, and the functional properties of the visual system. They provide a reliable and objective measure of visual processing and attention. The methodology is relatively simple to implement and analyze, making it a valuable tool for both clinical and research settings.