Abstract
Neuromagnetic responses related to the omission of the second sound in triplet of speech sounds were recorded. Three sets of stimuli, which were named as standard, deviant, and omission, consisted of three short Japanese speech sounds. The standard stimuli were consisted of /aoi/, meaning “blue” in Japanese. The deviant stimuli were consisted of /akai/, meaning “red.” The omission stimuli were consisted of /a_i/ (here, /_/ represented the omission of sound). Six male subjects (age range of 23-41) with normal hearing participated in the measurements. Stimuli were presented binaurally, while neuromagnetic responses were recorded over their right and left temporal sides, simultaneously. The responses were separately averaged by standard, deviant and omission. In the omission response, a component related to the omission of the speech sound was observed over the right and/or left hemispheres in 5 of 6 subjects, although its amplitude was very weak. In the subtracted waveforms, i. e., after subtraction of the omission responses from the standard responses, enlarged components were observed in the latency of 258-702msec referenced to the onset of the second sound of the standard stimuli. Equivalent Current Dipoles (ECDs) of the components, which exhibited dipolar field, were estimated in the right hemisphere of two subjects and in the left hemisphere of one subject. The estimated locations of the ECDs seemed to indicate the neural activities in the vicinity of the insula and in the superior temporal sulcus (STS). These results together with other previous studies suggested that STS may subserve a function at sensory level, while the insula may be related to the higher functions such as discrimination of stimuli.
