Glossary
Electroencephalography (EEG)
What is electroencephalography?
Electroencephalography (EEG) records voltage differences through electrodes on the scalp. The resulting recording is an electroencephalogram. The signal reflects electrical activity from populations of neurons, with changes visible on the scale of milliseconds.
How it works
Researchers use EEG to examine rhythmic activity and responses tied to particular events. It is especially useful for studying timing. Locating the source of a signal is harder and depends on the recording and analysis; eye and muscle activity can also enter the recording.
For example, a researcher might compare responses after correct and incorrect button presses. An error-related negativity can follow an incorrect response. As Wessel’s review of error awareness explains, the timing of that signal alone does not tell us when the person consciously recognized the mistake.
EEG and brain-computer interfaces
EEG can also supply signals to a brain-computer interface. In an early example, Farwell and Donchin (1988) described a character-selection task that used the P300 event-related potential. The system inferred which flashing item a participant was attending to. It did not read an unrestricted thought or recover the meaning of private mental content.
Why it matters
EEG lets researchers study rapid changes that behavior alone can leave hidden. It is also used clinically, including in epilepsy and sleep assessment. Its value comes from interpreting the signal alongside the task or clinical situation.