Scalp electrodes record the subject’s brain electrical activity during the task. The electrical signals are processed electronically and displayed as undulating lines, each line forming a series of peaks (positive waves) and valleys (negative waves). Waves, or components,2 are named according to their polarity—positive (P) or negative (N)—and their latency. Latency is the interval, in thousandths of a second (milliseconds [msec]) between the occurrence of a stimulus and the peak of the wave.
