DEVELOPMENT OF A MEMORY TRACE FOR A COMPLEX SOUND IN THE HUMAN BRAIN

THE development of a memory trace for a complex, unfamiliar sound in t he human brain was studied by repeatedly presenting reading subjects w ith this sound ('standard') which was occasionally replaced by a sligh tly different sound ('deviant'). Deviants did not elicit the mismatch negativity, an index of automatic change detection in auditory cortex, in the beginning but did later during the session. This result reflec ts a gradual 'sharpening' of sensory information encoded in the memory trace: the representation of the standard stimulus eventually became precise enough to enable the cortical change-detector mechanism to det ect a slight different stimulus.