Brain-activated technology. Electroencephalogram (EEG) trace of a subject, showing brain activity in the range of 0 to 25 Hz (cycles per second). At the centre of the frame is the area corresponding to 13.25 Hz which is being stimulated by a flashing light. This subject, however, is able to suppress the response to the light (seen as small peaks). This is the result of training using biofeedback techniques. The suppressed response at this frequency may be detected and used to activate a computer - in this case it is used to command a flight simulator to turn left. Compare with SPL picture ref. T498/005.