Auditory-evoked magnetic fields in relation to the interaural cross correlation

Abstract

Noninvasive measurements utilizing magnetoencephalography (MEG) have been used to study how sound stimulus features are represented in the human brain. These measurements have successfully revealed how, for example, tone frequency, periodicity, and intensity are encoded. Here, the auditory-evoked magnetic fields in change of the magnitude of the interaural cross correlation (IACC) were analyzed. The IACC of the stimuli was controlled by mixing two independent bandpass noises in appropriate ratios. The auditory stimuli were binaurally delivered through silicon tubes and earpieces inserted into the ear canals. All source signals had the same sound-pressure level. Nine volunteers with normal hearing took part in this study. The auditory-evoked fields were recorded using a neuromagnetometer in a magnetically shielded room. Combinations of a reference stimulus (IACC=1.0) and test stimuli (IACC=0.2,0.6,0.85) were presented alternately at a constant 0.5-s interstimulus interval, and the MEGs were recorded and averaged more than 50 times. The results showed that the peak amplitude of N1m, which was found above left and right temporal lobes around 100 ms after the stimulus onset, significantly decreased with increasing IACC. The N1m latencies were not affected by IACC.