The effect of center frequency and bandwidth on the auditory evoked magnetic field

Auditory evoked magnetic fields in relation to the center frequency of sound with a certain bandwidth were examined by magnetoencephalography (MEG). Octave band, 1/3 octave band, and 130 Hz bandwidth noises were used as the sound stimuli. All signals were presented at 60 dB SPL. The stimulus duration was 500 ms, with rise and fall ramps of 10 ms. Ten normal-hearing subjects took part in the study. Auditory evoked fields were recorded using a 122 channel whole-head magnetometer in a magnetically shielded room. The latencies, source strengths and coordinates of the N1m wave, which was found above the left and right temporal lobes around 100 ms after the stimulus onset, were analyzed. The results demonstrated that the middle frequency range had shorter N1m latencies and larger N1m amplitudes, and that the lower and higher frequency stimuli had relatively delayed N1m latencies and decreased N1m amplitudes. The N1m amplitudes correlated well to the loudness values in the frequency ranges between 250 and 2000 Hz. The source locations of N1m did not reveal any systematic changes related to the center frequency and bandwidth.