The technique involves using sound waves to entrain brain waves. Wearing headphones, Monroe claimed that brains respond by producing a third sound (called binaural beats) that encouraged various brainwave activity changes. In 2002, a University of Virginia presentation at the Society for Psychophysiologial Research examined Monroe's claim. The presentation demonstrated that EEG changes did not occur when the standard electromagnetic headphones of Monroe's setup were replaced by air conduction headphones, which were connected to a remote transducer by rubber tubes. This suggests that the basis for the entrainment effects is electromagnetic rather than acoustical.