[求助]请各位前辈高人指点一下听觉中的调谐失真是什么意思？

请各位前辈高人指点一下听觉中的调谐失真是什么意思？感激万分！

"调谐失真"的英文是什么?

harmonic distortion

下面的一段文字是与 Harmonic distortion 有关的一篇论文的  INTRODUCTION 希望对你有帮助

该论文的连接是http://jp.physoc.org/cgi/content/full/509/1/277

Healthy mammalian cochleae process sounds in a level-dependent manner: quiet sounds are amplified by active processes in cochlear mechanics, while loud sounds are not (Kim, Molnar & Matthews, 1980; Davis, 1983; for reviews see Patuzzi & Robertson, 1988; de Boer, 1991; Dallos, 1992). The device which is responsible for the mechanical amplification is known as the cochlear amplifier (after Davis, 1983). The precise mechanisms of this amplifier are not yet fully understood, although many of the amplifier's characteristics are well known. At each point along the length of the cochlea, for example, amplification occurs only for certain frequencies of sound: components of a sound with frequencies close to a particular location's 'best' or most sensitive frequency can be amplified substantially, while components with lower frequencies undergo little or no amplification (Rhode, 1971; Sellick, Patuzzi & Johnstone, 1982; Robles, Ruggero & Rich, 1986; Ruggero, Rich, Recio, Narayan & Robles, 1997). The amount of amplification that occurs also depends on the physiological condition of the cochlea: the cochlear amplifier is particularly vulnerable to insults which impair the function of the outer hair cells in the organ of Corti (Patuzzi, Yates & Johnstone, 1989; Ruggero & Rich, 1991; Dallos, 1992).

The gain of the cochlear amplifier can be defined as the difference between the sensitivities of the mechanical responses in 'passive' and 'active' cochleae (Davis, 1983; for the purposes of the present report, 'active' can be read as living, and 'passive' as dead). This gain is normally highest at low sound pressure levels (within 20 dB of hearing thresholds) and reduces progressively as sound pressure levels increase beyond 20 dB above threshold (cf. Nuttall & Dolan, 1996; Ruggero et al. 1997; also see Figs 1 and 4 in the present report). One highly beneficial consequence of this is that the mechanics of the cochlea can compress a very wide range of stimulus intensities into a much smaller range of response amplitudes: in effect, the mechanical compression allows the gap between the thresholds of hearing and those of pain to be expanded by several orders of magnitude (Davis, 1983; Zwicker, 1986; Yates, 1990).

The non-linearities associated with the operation of the cochlear amplifier (e.g. its level-dependent gain) have several consequences in addition to the compression described above. Most notably, the non-linearities must distort the incoming sounds to some extent. One well-known consequence of this is the existence of inter-modulation (or two-tone) distortion products in the cochlea (Goldstein, 1967; Kim et al. 1980; Robles, Ruggero & Rich, 1991). Another likely, or at least possible, consequence is harmonic distortion. This type of distortion has been observed in the receptor potentials of the inner and outer hair cells of the cochlea (Dallos & Cheatham, 1989; Cody & Russell, 1992), as well as in the discharge patterns of single cochlear nerve fibres (see Kiang, Liberman, Sewell & Guinan, 1986). Harmonic distortion can also be perceived (as 'overtones') when pure tones are presented in psychophysical experiments (cf. Wegel & Lane, 1924). It is not easy to relate the distortion observed in any of these experiments to the operation of the cochlear amplifier, however, since each stage of the auditory periphery which operates in a non-linear fashion will introduce additional distortion to the signal-processing cascade. Mechano-electrical transduction in the hair cells is likely to obscure any mechanically generated distortion, for example, and synaptic transmission from the hair cells to the afferent nerve fibres is likely to obscure any distortion that is either generated or present at the hair cell level. This is unfortunate, since knowledge of the distortion in the mechanics of the cochlea could provide considerable insight into the workings of the cochlear amplifier (cf. Nobili & Mammano, 1996; Zwislocki, Szymko & Hertig, 1997).

Direct observations of harmonic distortion in the mechanics of the cochlea have been made on several occasions in the past (e.g. see LePage, 1987; Khanna, Ulfendahl & Flock, 1989; Gummer, Hemmert, Morioka, Reis, Reuter & Zenner, 1993). Unfortunately, however, most of these observations have been made in physiologically compromised preparations (as evidenced by the lack of compression in the responses to pure tones, for example). Only two series of observations have been reported from truly active (i.e. physiologically normal) cochleae (Cooper & Rhode, 1992; Ruggero et al. 1997), and even these are limited in scope. Cooper & Rhode's (1992) observations on the feline basilar membrane were restricted to stimulus frequencies well below the preparation's best frequency, for example, and the distortion at these frequencies only became significant ( > 1 % distortion) at sound pressure levels in excess of 90-100 dB SPL (sound pressure level in decibels, where 0 dB SPL = 20 µa). This finding is not surprising, as the effects of the cochlear amplifier are known to be limited at low frequencies (see above) and the harmonic distortion levels might well be expected to be low in the absence of significant amplification. The observations made in the chinchilla cochlea by Ruggero et al. (1997) suggest that the amount of harmonic distortion is low even when the cochlear amplifier is hard at work: Ruggero et al. do not give precise values for the distortion evoked by best-frequency tones, but they infer that the distortion is much lower than -20 to -30 dB relative to the fundamental responses (the limits of their measurement system under suboptimal recording conditions; cf. Ruggero et al. 1997, p. 2153).

The study described in the present report uses a purpose-built displacement-sensitive laser interferometer to probe the mechanics of the living guinea-pig cochlea. The high fidelity of this equipment permits detailed investigations of harmonic distortion in truly active (i.e. physiologically normal) cochleae. The principal findings are that best-frequency tones undergo up to 4 % distortion in healthy cochleae, and that this figure drops to less than 1 % in compromised cochleae. The observed distortion patterns are shown to be compatible with a highly simplified model of cochlear mechanics, which incorporates physiologically plausible non-linearities into a positive feedback loop (based on the proposals of Zwicker, 1986).

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