Magnetoencephalographic Study on the Representation of Huygens Noise in the Auditory Cortex of Humans
Processing and representation of pitch in human was studied by using regular interval sounds (RIS-Huygens noise). The distinct pitch of RIS is introduced by delaying random noise and adding it back to the same noise. The relation between the psychoacoustically measured pitch of RIS and the auditory evoked neuromagnetic responses was investigated. The pitch specific onset response (POR) was derived by means of magnetoencephalography (MEG). Source analysis revealed the center of this activity in the lateral part of Heschl's Gyrus in the auditory cortex of both hemispheres. The latency of the POR correlated highly with the perceived pitch. When the perceived pitch of RIS decreased, the latency of the POR increased. In a second experiment, the influence of timbre on perception and the POR was investigated. An increase of the perceived pitch resulted in an increase of the POR-latency, when the center frequency of the bandpass filter was increased. These results indicate that the POR integrates both, pitch and timbre and, thus, POR is an objective neurophysiological representation of the perception of a sound. Simulations of pitch processing showed, that temporal pitch models can account for the perceived pitch of RIS but fail to simulate timbre-induced pitch changes. Hence, MEG provides valuable parameters which could be integrated in models of pitch processing.
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