Time course of loudness in tone patterns is automatically represented by the human brain.

The present study investigated the neural mechanisms of intensity coding by presenting human subjects repetitively with tone pairs consisting of two tones differing in intensity. The first tone was higher in sound pressure level than the second (70 versus 58 dB SPL). Infrequent order reversals of the two tones elicited the mismatch negativity (MMN), an event-related brain potential probe of preattentive auditory sensory memory. This finding indicates that the human auditory system automatically encodes information about the time course of intensity within tone patterns into neural representations.