Automatic auditory processing and event-related brain potentials in persons with mental retardation.

Measuring event-related brain potentials, this study examined automatic auditory processing in adults with and without mental retardation. Using an auditory oddball paradigm under an inattentive condition, we anticipated that an enhanced negative potential would be followed by a relatively small positive potential. The former was considered as the mismatch negativity and the latter as the P3a. Retarded adults (1 woman, 6 men, defined as a range of moderate to profound retardation) and 8 nonretarded (2 women, 6 men) adults participated. The mismatch negativity showed smaller amplitudes and greater latencies for retarded persons than those for nonretarded adults, whereas the P3a for the groups was comparable. The results may suggest malfunction of automatic auditory change-detection of the brain in mentally retarded persons.