Neuromagnetic Responses Elicited by Tones and Chords of Different Intensities and Frequency Components

摘要

Auditory cortical response is modulated as a function of stimulus sound intensity. It is therefore necessary to adjust the sound intensity levels when effects of other acoustic parameters of stimulus sounds or endogenous factors such as attention are investigated in the auditory experiments. Sound intensity can be defined by several parameters such as temporal peak intensity, RMS intensity and spectral peak intensity of frequency component(s). These physical intensities are further expressed in the perceptual domain as sensation levels. However, it is not yet known as to which parameter is most associated with the MEG response evoked in the auditory cortex, especially when the number of frequency components is interactively increased. Here, we performed MEG experiments to compare the amplitude of Nlm response elicited by nine kinds of stimulus sounds, varying in three levels of intensity and/or number of frequency components. As results, the amplitudes of the Nlm response were increased as the stimulus sound intensities were increased. Specifically, significant and highest positive correlation was found between the Nlm moment of the right hemisphere and the sound sensation level, indicating that the Nlm response reflects perceptual loudness rather than the physical intensity. Interestingly, the spectral peak intensity also showed a positive correlation with the Nlm moment as high and significant as the sensation levels did. These results suggest that the spectral peak intensity is the most reliable parameter to adjust the stimulus sound intensity in the auditory experiment.