Do event-related potentials reveal the mechanism of the auditory sensory memory in the human brain?

Event-related brain potentials (ERP) to task-irrelevant tone pips presented at short intervals were recorded from the scalp of normal human subjects. Infrequent decrements in stimulus intensity elicited the mismatch negativity (MMN) which was larger in amplitude and shorter in latency the softer the deviant stimulus was. The results obtained imply memory representations which develop automatically and accurately represent the physical features of the repetitive stimulus. These memory traces appear to be those of the acoustic sensory memory, the 'echoic' memory. When an input does not match with such a trace the MMN is generated.