Neural processes of auditory scene analysis observed by magnetencephalography

Abstract

Auditory‐evoked magnetic field elicited by three sound stimuli consisting of a spoken word, a click, and their overlapping version, was measured using BTi 37ch SQUID MEG system from the contra lateral hemisphere of the stimulated ears of seven normal hearing subjects. Three stimuli were presented in a random order with a random interstimulus interval between 1 and 2 s at the most comfortable hearing level. Two tasks were imposed: One is to count the click, and the other is to count the spoken word. Significant differences in the response were observed between the tasks. For both the tasks, a neural activity in the left and right temporal auditory cortices was observed for all the stimuli. When counting the click, a wide spread activity was elicited by the overlapping click suggesting possible contribution of a frontal neural activity in the right hemisphere. The results suggest that plural neural mechanisms may concern the auditory scene analysis by which the overlapping sound objects are distinctively perceived. The temporal‐lobe activity may reflect automatic memory trace construction, and the frontal‐lobe activity may concern attentional selection of a memory trace.