Latency variation of auditory N1m responses to vocal and nonvocal sounds.

To investigate the temporal aspect of timbre processing, we recorded auditory-evoked neuromagnetic responses to periodic complex sounds, which were matched in all acoustic parameters except for two fundamental frequencies (F0s) and 12 spectral envelopes of vocal and nonvocal categories. Only for nonvocal sounds, a significant difference in N1m latency for F0 was detected in both hemispheres. A significant difference among stimuli was detected in both hemispheres for vocal and linear sounds, whereas only in the right hemisphere for instrumental sounds. Moreover, the results of paired comparison among F0s revealed that not only the vocal sounds but also some of the nonvocal sounds were F0-independent. This latency independence may be attributed to the relatively high power in the higher frequency spectrum.