Variability of single event-related brain potentials

Electrical responses of the brain to stimuli can be conceived as deterministic low-amplitude signals embedded in colored noise. Subjects are repeatedly stimulated to extract the brain´s response by averaging. The authors address the issue that single responses may vary from trial-to-trial. Three statistical tests are defined and their theoretical properties are given. Simulations based on real data demonstrate the tests´ empirical validity and their differential sensitivity to different types of signal variation. A real data application shows that substantial variations were present even in a simple experimental setting.<>