Cortical Pitch Regions in Humans Respond Primarily to Resolved Harmonics and Are Located in Specific Tonotopic Regions of Anterior Auditory Cortex

Abstract

Pitch is a defining perceptual property of many real-world sounds, including music and speech. Classically, theories of pitch perception have differentiated between temporal and spectral cues. These cues are rendered distinct by the frequency resolution of the ear, such that some frequencies produce "resolved" peaks of excitation in the cochlea, whereas others are "unresolved," providing a pitch cue only via their temporal fluctuations. Despite longstanding interest, the neural structures that process pitch, and their relationship to these cues, have remained controversial. Here, using fMRI in humans, we report the following: (1) consistent with previous reports, all subjects exhibited pitch-sensitive cortical regions that responded substantially more to harmonic tones than frequency-matched noise; (2) the response of these regions was mainly driven by spectrally resolved harmonics, although they also exhibited a weak but consistent response to unresolved harmonics relative to noise; (3) the response of pitch-sensitive regions to a parametric manipulation of resolvability tracked psychophysical discrimination thresholds for the same stimuli; and (4) pitch-sensitive regions were localized to specific tonotopic regions of anterior auditory cortex, extending from a low-frequency region of primary auditory cortex into a more anterior and less frequency-selective region of nonprimary auditory cortex. These results demonstrate that cortical pitch responses are located in a stereotyped region of anterior auditory cortex and are predominantly driven by resolved frequency components in a way that mirrors behavior.Key words: pitch; auditory cortex; fMRI; tonotopy; resolved harmonics; periodicity IntroductionPitch is the perceptual correlate of periodicity (repetition in time), and is a fundamental component of human hearing (Plack et al., 2005). Many real-world sounds, including speech, music, animal vocalizations, and machine noises, are periodic, and are perceived as having a pitch corresponding to the repetition rate (the fundamental frequency or F0). Pitch is used to identify voices, to convey vocal emotion and musical structure, and to segregate and track sounds in auditory scenes. Here we investigate the cortical basis of pitch perception in humans.When represented in the frequency domain, periodic sounds exhibit a characteristic pattern: power is concentrated at harmonics (multiples) of the fundamental frequency. Because the cochlea filters sounds into frequency bands of limited resolution, the frequency and time domain can in principle provide distinct information (Fig. 1). Models of pitch perception have thus focused on the relative importance of temporal versus spectral (frequency-based) pitch cues (Goldstein, 1973;Terhardt, 1974; Meddis and Hewitt, 1991; Patterson et al., 1992; Bernstein and Oxenham, 2005). A central finding in this debate is that sounds with perfect temporal periodicity, but with harmonics that are spaced too closely to be resolved by the cochlea, produce only a weak pitch percept (Houtsma a...

Whispering - The hidden side of auditory communication

“…HG activity is in accordance with the activity found for voiced relative to synthesized whispered vocalizations in the anterolateral HG (von Kriegstein et al, 2010), but here we report a much more extended activity in response to natural voiced and whispered vocalizations. The activity inside the tonotopic fields might represent the higher spectral regularity of voiced vocalizations (Norman-Haignere et al, 2013) that determines the perception of pitch. Pitch and pitch salience are predominantly used in listeners to classify affective vocalizations (Banse and Scherer, 1996;Vestergaard and Patterson, 2009).…”

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“…Some initial recent work has found that HCNNs trained to solve challenging high-variation word recognition tasks are predictive of voxel patterns in auditory cortex (54). These models are also able to differentiate auditory areas, with lower model layers more predictive of inferior colliculus, intermediate layers more predictive of primary auditory cortex, and higher layers of speech and music-selective areas identified in recent imaging studies (55).…”

“…As with higher visual areas, models can be used to make detailed testable predictions about poorly-understood auditory cortex subregions, especially in relation to speech and natural sound representations (55,56). This problem could be approached experimentally using both human fMRI/eCOG and non-human primate electrophysiology techniques.…”

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