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Across-channel timing differences as a potential code for the frequency of pure tones.

Carlyon RP, Long CJ, Micheyl C - J. Assoc. Res. Otolaryngol. (2011)

Bottom Line: When a pure tone or low-numbered harmonic is presented to a listener, the resulting travelling wave in the cochlea slows down at the portion of the basilar membrane (BM) tuned to the input frequency due to the filtering properties of the BM.It has been suggested that the auditory system exploits these across-channel timing differences to encode the pitch of both pure tones and resolved harmonics in complex tones.We conclude that although the use of across-channel timing cues provides an a priori attractive and plausible means of encoding pitch, many of the most obvious metrics for using that cue produce pitch estimates that are strongly influenced by the overall level and therefore are unlikely to provide a straightforward means for encoding the pitch of pure tones.

View Article: PubMed Central - PubMed

Affiliation: MRC Cognition & Brain Sciences Unit, 15 Chaucer Rd., Cambridge, CB2 7EF, UK. bob.carlyon@mrc-cbu.cam.ac.uk

ABSTRACT
When a pure tone or low-numbered harmonic is presented to a listener, the resulting travelling wave in the cochlea slows down at the portion of the basilar membrane (BM) tuned to the input frequency due to the filtering properties of the BM. This slowing is reflected in the phase of the response of neurons across the auditory nerve (AN) array. It has been suggested that the auditory system exploits these across-channel timing differences to encode the pitch of both pure tones and resolved harmonics in complex tones. Here, we report a quantitative analysis of previously published data on the response of guinea pig AN fibres, of a range of characteristic frequencies, to pure tones of different frequencies and levels. We conclude that although the use of across-channel timing cues provides an a priori attractive and plausible means of encoding pitch, many of the most obvious metrics for using that cue produce pitch estimates that are strongly influenced by the overall level and therefore are unlikely to provide a straightforward means for encoding the pitch of pure tones.

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Slope of the phase transition as a function of level and input frequency. The curves shown are derived from the best-fitting model described in the text for input frequencies spaced 3 semitones apart, starting at 250 Hz, and with levels of 50, 70 and 90 dB SPL.
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Fig8: Slope of the phase transition as a function of level and input frequency. The curves shown are derived from the best-fitting model described in the text for input frequencies spaced 3 semitones apart, starting at 250 Hz, and with levels of 50, 70 and 90 dB SPL.

Mentions: As shown in Figure 8, the slopes vary as functions both of level and of fs. The slopes are slightly shallower (less negative) at lower frequencies, presumably because, in the GP, the relative bandwidths of frequency tuning curves (e.g. as summarized by Shera et al. 2002) are broader at low frequencies. The slopes also become shallower (less negative) with increases in level, as would be expected with the decrease in frequency selectivity at high levels (Rhode 1971; Robles et al. 1986). Both of these effects were sufficiently reliable to produce significant main effects when the slope values for three levels (50, 70, 90 dB SPL) and for ten values of fs spaced in units of 0.1 log10fs were entered into a generalized linear model (effect of fs: F1,28 = 28.9, P < 0.00001; effect of level: F1,28 = 22.1, P < 0.00001). Averaged across fs, slopes varied by a factor of 1.67 across level, approaching the factor of 2.07 for the variation with fs. Hence, any attempt to estimate fs based on a metric related to the slope—for example by estimating the difference along the AN array between fibers that responded in phase—would be strongly influenced by the input level.FIG. 8


Across-channel timing differences as a potential code for the frequency of pure tones.

Carlyon RP, Long CJ, Micheyl C - J. Assoc. Res. Otolaryngol. (2011)

Slope of the phase transition as a function of level and input frequency. The curves shown are derived from the best-fitting model described in the text for input frequencies spaced 3 semitones apart, starting at 250 Hz, and with levels of 50, 70 and 90 dB SPL.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3298616&req=5

Fig8: Slope of the phase transition as a function of level and input frequency. The curves shown are derived from the best-fitting model described in the text for input frequencies spaced 3 semitones apart, starting at 250 Hz, and with levels of 50, 70 and 90 dB SPL.
Mentions: As shown in Figure 8, the slopes vary as functions both of level and of fs. The slopes are slightly shallower (less negative) at lower frequencies, presumably because, in the GP, the relative bandwidths of frequency tuning curves (e.g. as summarized by Shera et al. 2002) are broader at low frequencies. The slopes also become shallower (less negative) with increases in level, as would be expected with the decrease in frequency selectivity at high levels (Rhode 1971; Robles et al. 1986). Both of these effects were sufficiently reliable to produce significant main effects when the slope values for three levels (50, 70, 90 dB SPL) and for ten values of fs spaced in units of 0.1 log10fs were entered into a generalized linear model (effect of fs: F1,28 = 28.9, P < 0.00001; effect of level: F1,28 = 22.1, P < 0.00001). Averaged across fs, slopes varied by a factor of 1.67 across level, approaching the factor of 2.07 for the variation with fs. Hence, any attempt to estimate fs based on a metric related to the slope—for example by estimating the difference along the AN array between fibers that responded in phase—would be strongly influenced by the input level.FIG. 8

Bottom Line: When a pure tone or low-numbered harmonic is presented to a listener, the resulting travelling wave in the cochlea slows down at the portion of the basilar membrane (BM) tuned to the input frequency due to the filtering properties of the BM.It has been suggested that the auditory system exploits these across-channel timing differences to encode the pitch of both pure tones and resolved harmonics in complex tones.We conclude that although the use of across-channel timing cues provides an a priori attractive and plausible means of encoding pitch, many of the most obvious metrics for using that cue produce pitch estimates that are strongly influenced by the overall level and therefore are unlikely to provide a straightforward means for encoding the pitch of pure tones.

View Article: PubMed Central - PubMed

Affiliation: MRC Cognition & Brain Sciences Unit, 15 Chaucer Rd., Cambridge, CB2 7EF, UK. bob.carlyon@mrc-cbu.cam.ac.uk

ABSTRACT
When a pure tone or low-numbered harmonic is presented to a listener, the resulting travelling wave in the cochlea slows down at the portion of the basilar membrane (BM) tuned to the input frequency due to the filtering properties of the BM. This slowing is reflected in the phase of the response of neurons across the auditory nerve (AN) array. It has been suggested that the auditory system exploits these across-channel timing differences to encode the pitch of both pure tones and resolved harmonics in complex tones. Here, we report a quantitative analysis of previously published data on the response of guinea pig AN fibres, of a range of characteristic frequencies, to pure tones of different frequencies and levels. We conclude that although the use of across-channel timing cues provides an a priori attractive and plausible means of encoding pitch, many of the most obvious metrics for using that cue produce pitch estimates that are strongly influenced by the overall level and therefore are unlikely to provide a straightforward means for encoding the pitch of pure tones.

Show MeSH