RESPONSES OF THE HUMAN AUDITORY-CORTEX TO CHANGES IN ONE VERSUS 2 STIMULUS FEATURES

Neuromagnetic responses were recorded with a 24-SQUID magnetometer in two ''oddball'' experiments to determine whether mismatch responses to changes in single stimulus features are additive. In experiment 1, th e one-feature deviants differed from standards in interstimulus interv al (ISI) or frequency, and the two-feature deviants in both ISI and fr equence. In experiment 2, deviants differed in duration, frequency, or both. All deviants evoked a mismatch field (MMF) with sources close t o each other in the supratemporal auditory cortex. Except for the ISI deviants, the MMF sources were about I cm anterior to the source of th e 100-ms response, N100m, to the standards. In the two experiments, MM Fs obtained in response to the two-feature deviants resembled closely the sum of MMFs in response to one-feature deviants. The results sugge st that the standards leave a multiple neuronal representation in the human auditory cortex. The particular neuronal traces of the represent ation react independently to changes in different features of sound st imuli.