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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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From Kim et al. (1980), with permission. Phase of AN response to a 2,100 + 2,700-Hz complex at levels ranging from 4 to 74 dB SPL. There are two sets of curves, corresponding to each component; the curves within each set are for different sound levels and, at the scale shown here, appear to overlap. Note that, unlike all the other Figs. in this article, CF decreases from high to low along the abscissa.
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Fig1: From Kim et al. (1980), with permission. Phase of AN response to a 2,100 + 2,700-Hz complex at levels ranging from 4 to 74 dB SPL. There are two sets of curves, corresponding to each component; the curves within each set are for different sound levels and, at the scale shown here, appear to overlap. Note that, unlike all the other Figs. in this article, CF decreases from high to low along the abscissa.

Mentions: The pros and cons of the above arguments have been debated extensively elsewhere (Moore 2003; de Cheveigné 2005; Plack 2005). Here, we simply note that the various potential weaknesses of the two traditional approaches have led to considerable interest in an alternative class of explanation, whereby the auditory system performs an instantaneous comparison of the temporal pattern of firing in auditory neurons having different CFs (Loeb et al. 1983; Shamma 1985; Carney 1994; Heinz et al. 2001; Carney et al. 2002; Colburn et al. 2003; Oxenham et al. 2004; Loeb 2005; Moore and Carlyon 2005; Cedolin and Delgutte 2010). This idea stems from the fact that the phase of AN responses varies across CF in a manner that varies with the input frequency. It can be illustrated with reference to Figure 1, reprinted from an article by Kim et al. (1980), who recorded the responses of cat AN fibres having a wide range of CFs to a two-tone complex having component frequencies, f1 = 2,100 Hz and f2 = 2,700 Hz. The figure shows two sets of curves, each of which represents the phase of the AN response to one of the components. In each case, the phase is roughly constant over a range of high-frequency CFs, and there is a steep phase transition (PT) at CFs near the frequency of each tonal component (shown by the small arrows); similar results have been more recently obtained by van der Heijden and Joris (2006) using a different technique. To a first approximation, this pattern of results can be explained by the facts that a filter introduces a delay as the frequency of the input passes through its resonance, that the size of this delay is greater for narrow than for broad filters, and that the bandwidths of basilar membrane (BM) filters (as estimated from, e.g. tuning curves), when expressed in hertz, are narrower at the apex than at the base. A consequence of the variation in phase with CF is that neurons with CFs much higher than the input frequency fire at approximately the same time as each other, whereas those close to the input frequency fire out of phase. This is illustrated in Figure 2 which shows schematic “neurograms” to 1,000- and 1,200-Hz pure tones (these neurograms were not derived from the cat data obtained by Kim et al. and shown in Figure 1, but were based on fits to data obtained from another species as described in “Modelling approach”).FIG. 1


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)

From Kim et al. (1980), with permission. Phase of AN response to a 2,100 + 2,700-Hz complex at levels ranging from 4 to 74 dB SPL. There are two sets of curves, corresponding to each component; the curves within each set are for different sound levels and, at the scale shown here, appear to overlap. Note that, unlike all the other Figs. in this article, CF decreases from high to low along the abscissa.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3298616&req=5

Fig1: From Kim et al. (1980), with permission. Phase of AN response to a 2,100 + 2,700-Hz complex at levels ranging from 4 to 74 dB SPL. There are two sets of curves, corresponding to each component; the curves within each set are for different sound levels and, at the scale shown here, appear to overlap. Note that, unlike all the other Figs. in this article, CF decreases from high to low along the abscissa.
Mentions: The pros and cons of the above arguments have been debated extensively elsewhere (Moore 2003; de Cheveigné 2005; Plack 2005). Here, we simply note that the various potential weaknesses of the two traditional approaches have led to considerable interest in an alternative class of explanation, whereby the auditory system performs an instantaneous comparison of the temporal pattern of firing in auditory neurons having different CFs (Loeb et al. 1983; Shamma 1985; Carney 1994; Heinz et al. 2001; Carney et al. 2002; Colburn et al. 2003; Oxenham et al. 2004; Loeb 2005; Moore and Carlyon 2005; Cedolin and Delgutte 2010). This idea stems from the fact that the phase of AN responses varies across CF in a manner that varies with the input frequency. It can be illustrated with reference to Figure 1, reprinted from an article by Kim et al. (1980), who recorded the responses of cat AN fibres having a wide range of CFs to a two-tone complex having component frequencies, f1 = 2,100 Hz and f2 = 2,700 Hz. The figure shows two sets of curves, each of which represents the phase of the AN response to one of the components. In each case, the phase is roughly constant over a range of high-frequency CFs, and there is a steep phase transition (PT) at CFs near the frequency of each tonal component (shown by the small arrows); similar results have been more recently obtained by van der Heijden and Joris (2006) using a different technique. To a first approximation, this pattern of results can be explained by the facts that a filter introduces a delay as the frequency of the input passes through its resonance, that the size of this delay is greater for narrow than for broad filters, and that the bandwidths of basilar membrane (BM) filters (as estimated from, e.g. tuning curves), when expressed in hertz, are narrower at the apex than at the base. A consequence of the variation in phase with CF is that neurons with CFs much higher than the input frequency fire at approximately the same time as each other, whereas those close to the input frequency fire out of phase. This is illustrated in Figure 2 which shows schematic “neurograms” to 1,000- and 1,200-Hz pure tones (these neurograms were not derived from the cat data obtained by Kim et al. and shown in Figure 1, but were based on fits to data obtained from another species as described in “Modelling approach”).FIG. 1

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