NEUROPHYSIOLOGIC BASES OF SPEECH-DISCRIMINATION

The mismatch negativity (MMN) is an automatic cortical evoked potentia l that signifies the brain's detection of acoustic change. In other wo rds, the MMN reflects the neurophysiologic processes that underlie aud itory discrimination. As such, the MMN provides an objective tool for evaluating central auditory mechanisms involved in speech perception. We are using the MMN to study the central auditory processes that enco de acoustic changes important for speech perception in 1) normal-heari ng adults and children, 2) individuals with impaired auditory systems (including persons with learning disabilities, attention deficit disor ders, cochlear implants), and 3) an animal model, Specifically, we hav e demonstrated that the MMN provides information about the central pro cessing of fine acoustic differences, the neuroanatomic pathways that encode acoustic change, central auditory processing in the presence of peripheral hearing deficits, and central auditory system plasticity. In addition, we have considered methodological challenges associated w ith measuring the MMN in individual subjects. Several methodological i ssues-including appropriate stimuli, stimulus presentation variables, the recording protocol and environment, and validation of the MMN in i ndividuals-are discussed.