Dynamic sensory updating in the auditory system.

Typically, in everyday situations, auditory input is constantly changing. Change is an important cue for the auditory system, which can signal the start of new sources of information or that some action may be required. Using an event-related brain potential that can be elicited whether or not attention is focused on the sounds (the mismatch negativity, MMN) we measured the time course of the effects of contextual changes on the brain's response to the same stimulus event. The onset or cessation of a sound in a stimulus block brought about context changes. The effect of the context was observed through changes in the MMN response to a deviant event that was present throughout the sound sequence. These results suggest the existence of a dynamic system of change detection, which updates its model of the sensory input on-line as the changes occur.