Dynamics of the auditory evoked potential and the auditory evoked neuromagnetic field obtained with the interstimulus interval of 300msec, in response to various kinds of natural sounds and artificial sounds, were investigated and the following results were obtained;
1) Remarkable left-right auditory evoked potential differences depending upon the physical characteristics of sounds were found, and this mechanism depends not on any higher function, but on a more basic function.
2) The results obtained by the above method were in complete agreement with those obtained by Tsunoda's key-tapping test.
3) In the noraml Japanese, the right hemisphere was dominant for the sounds with the following physical characteristics; (1) single formant (or formant-like structure) or simple attenuation in higher frequency ranges. (2) two or more formants (or formant-like structures) in harmonic relations. (3) small pitch fluctuations and rich harmonic structures, particularly, when sounds consist only of harmonic tones.
4) The most active area of N
1-components of the AEPs was in general the midtemporal in either the left or the right hemisphere in accordance with the relation between the physical characteristics of sounds and the left-right AEP differences. The most active area of P
1-components was more sensitive to the physical structures of sounds.
5) The gravity center of the equivalent current dipole corresponding to N
1-componint was estimated to be in or near the primary auditory cortex, while that to P
1-component was estimated to be in the acoustic radiation or its neighborhood. Left-right differences in the quantities of the tangential dipole moments corresponding to both P
1-and N
1-components were in agreement with those of the auditory evoked potentials.
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