From noise to pitch: transient and sustained responses of the auditory evoked field.

In recent magnetoencephalographic studies, we established a novel component of the auditory evoked field, which is elicited by a transition from noise to pitch in the absence of a change in energy. It is referred to as the 'pitch onset response'. To extend our understanding of pitch-related neural activity, we compared transient and sustained auditory evoked fields in response to a 2000-ms segment of noise and a subsequent 1000-ms segment of regular interval sound (RIS). RIS provokes the same long-term spectral representation in the auditory system as noise, but is distinguished by a definite pitch, the salience of which depends on the degree of temporal regularity. The stimuli were presented at three steps of increasing regularity and two spectral bandwidths. The auditory evoked fields were recorded from both cerebral hemispheres of twelve subjects with a 37-channel magnetoencephalographic system. Both the transient and the sustained components evoked by noise and RIS were sensitive to spectral bandwidth. Moreover, the pitch salience of the RIS systematically affected the pitch onset response, the sustained field, and the off-response. This indicates that the underlying neural generators reflect the emergence, persistence and offset of perceptual attributes derived from the temporal regularity of a sound.