neuronalrepofpitch - © 2005 Nature Publishing Group The...

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Unformatted text preview: © 2005 Nature Publishing Group The neuronal representation of pitch in primate auditory cortex Daniel Bendor 1 & Xiaoqin Wang 1 Pitch perception is critical for identifying and segregating audi- tory objects 1 , especially in the context of music and speech. The perception of pitch is not unique to humans and has been experimentally demonstrated in several animal species 2,3 . Pitch is the subjective attribute of a sound’s fundamental frequency ( f ) that is determined by both the temporal regularity and average repetition rate of its acoustic waveform. Spectrally dissimilar sounds can have the same pitch if they share a common f . Even when the acoustic energy at f is removed (‘missing fundamental’) the same pitch is still perceived 1 . Despite its importance for hearing, how pitch is represented in the cerebral cortex is unknown. Here we show the existence of neurons in the auditory cortex of marmoset monkeys that respond to both pure tones and missing fundamental harmonic complex sounds with the same f , providing a neural correlate for pitch constancy 1 . These pitch- selective neurons are located in a restricted low-frequency cortical region near the anterolateral border of the primary auditory cortex, and is consistent with the location of a pitch-selective area identified in recent imaging studies in humans 4,5 . Many natural sounds (or biologically significant sounds) have periodic acoustical waveforms. These sounds can be spectrally decomposed into a sinusoid at the frequency of periodicity ( f ) and a series of sinusoids at frequencies that are integer multiples of f (harmonics). Although these individual spectral components are represented within the cochleotopic organization of the auditory system in a distributed fashion, they are perceptually grouped together into a single sound with a pitch equivalent to a pure tone at f (ref. 1). In the auditory periphery, the f of complex sounds— such as missing fundamental harmonic complex sounds (MFs)—is represented by a distributed neural code involving both the discharge rates and temporal firing patterns of auditory nerve fibres 6,7 . How this information is used to encode pitch within the central auditory system is poorly understood. Deficits in pitch discrimination have been observed in animals 8 , including humans 9,10 , following auditory cortical lesions, indicating a cortical role in pitch perception. However, electrophysiological recordings in macaque monkeys suggest that primary auditory cortex (AI) does not contain a representation of pitch, as AI neurons do not respond to MFs with a pitch matching their characteristic frequency 11,12 . Alternatively, pitch may be processed in non-primary auditory cortex, as recent human imaging studies have revealed a cortical pitch processing region anterolateral to primary auditory cortex 4,5 . The organization of primary and secondary areas of auditory cortex is largely conserved across primate species 13,14 , and a similar ‘pitch centre’ may exist in non-human primate auditory...
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neuronalrepofpitch - © 2005 Nature Publishing Group The...

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