摘要:

Recent measurements obtained with a variety of techniques have extended von Békésy’s observations of cochlear‐partition mechanics including the traveling‐wave pattern and the frequency‐place relation. Whereas the cochlear filter has been shown to be sharper than expected, on the basis of Békésy’s results, it apparently is not sharp enough to account for the frequency selectivity observed in auditory nerve fibers. The main remaining question is whether the vibration of the basilar membrane is linear or not. Steady‐state nonlinearities that disappear rapidly upon death, transient nonlinear response, and two‐tone suppression have been observed in the mid‐frequency range in one animal species. Whether the linearity–nonlinearity controversy arises from a species difference or a frequency‐place difference remains to be resolved.

ISSN:0001-4966    

DOI:10.1121/1.384296

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Over the last five years, we have studied spatial distributions of cochlear responses to single‐ and two‐tone stimuli by recording sequentially from as many as 418 cochlear nerve fibers in each cat and obtaining plots of amplitude and phase of response components at primary and distortion frequencies. We have observed: (1) that such responses to two‐tone stimuli of sound pressure levels (SPL) as low as 34 dBre20 μN/m2rms show noticeable deviations from linear behavior; (2) that two major forms of nonlinear behavior in responses to two‐tone stimuli are distortion products and two‐tone suppression; (3) that the spatial distributions of amplitude and phase of (2f1‐f2) and (f2‐f1) components in response to two‐tone stimuli are similar, in the region near and apical to the distortion‐frequency place, to those of thefscomponent in response to a single‐tone stimulus whose frequencyfsis equal to the particular distortion frequency, and dissimilar in the more basal region; and (4) that each of thef1andf2components in the response is mutually suppressed in regions where the other response component is large. By examining acoustic signals near the eardrum of the cat and the chinchilla with a closed acoustic system containing a probe microphone, we have observed, with SPL of the primary frequencies ranging from 40 to 95 dB, that the levels of the acoustic distortion signals (2f1‐f2) and (f2‐f1) can be as large as −30 and −43 dB, respectively, relative to the primary levels. Our results from a model for the peripheral auditory system consisting of a two‐dimensional model for cochlear mechanics (with nonlinear equivalent basilar‐membrane damping) coupled to a linear model for middle ear and acoustic coupler show qualitative agreement with our animal data. These animal and model studies support the following interpretations: (1) mechanical distortion signals (2f1‐f2) and (f2‐f1) are generated in the cochlear region where thef1andf2components are both large; (2) these distortion signals propagate both apically toward the distortion‐frequency place and basally toward the stapes, through the middle ear and into the ear canal; and (3) mutual suppression of thef1andf2components and generation of the propagating distortion products are likely to be present concurrently in cochlear‐partition motion. We have also found that both neurally observed and acoustically observed distortion products are reversibly reduced by exposing the ear for 1 or 2 min to a fatiguing single tone at SPL of 80 to 90 dB at a frequency near or slightly below the primary frequencies. Observations of the effects of the single‐tone fatiguing and of anoxia on acoustic distortion signals demonstrate physiological vulnerability of mechanically present nonlinear behavior of the ear. Our results support the hypothesis that, in the mechanoelectrophysiological transduction occurring in the normal organ of Corti, response variables of the mechanical domain (e.g., basilar‐membrane motion) and of the electrophysiological domain (e.g., hair‐cell mambrane potential) are bidirectionally coupled such that nonlinear behavior originating from either domain produces effects that can also be observed in the other domain. One of the functionally useful effects of cochlear nonlinearity appears to be an increase in the dynamic range by compression of the amplitude of cochlear‐partition motion.

ISSN:0001-4966    

DOI:10.1121/1.384297

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

With advances in our understanding of the auditory periphery, models of cochlear mechanics have evolved from descriptions of existing data to the point that they can suggest meaningful observations that should be made and predict expected outcomes. As an example, we discuss relationships among mechanical nonlinearities in the inner ear, two‐tone suppression, and the auditory ’’second filter.’’ Electrophysiological two‐tone suppression data indicate that excitatory tuning curves (stimulus intensity required to elicit a specified amount of activity in a primary fiber as a function of frequency) are more sharply tuned than suppressive tuning curves (stimulus intensity required to suppress the response to a continuous tone at the fiber’s characteristic frequency by a specified amount as a function of frequency). Model simulations which attempt to account for the above difference suggest that there must be a stage of sharpening between the physical variable governing two‐tone suppression (tentatively identified as velocity of the basilar membrane) and the physical variable governing neural excitation. An experiment that would unequivocally demonstrate the simultaneous existence of two representations of the stimulus with significantly different tuning properties in the cochlea is described. The future evolution of cochlear modeling, incorporating nonlinear two‐dimensional models, is discussed.

ISSN:0001-4966    

DOI:10.1121/1.384298

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A new technique for measuring sound‐induced resistance changes (CR) in scala media in response to pure‐tone stimuli by injecting alternating current into guinea‐pig cochleas was reported recently [C. D. Geisleretal., J. Acoust. Soc. Am. 61, 1557–1566 (1977)]. Detailed measurements with this technique indicate that while the CR behaves approximately as does the cochlear microphonic (CM) there can be very significant differences between the two variables under certain experimental conditions. Computer analysis of simultaneously recorded CR voltage components and CM indicates that the CR harmonics, in both amplitude and phase, behaved differently with sound intensity and with asphyxia than did the CM harmonics (A. E. Hubbardetal., J. Acoust. Soc. Am 66, 431–445 (1979)]. Direct current injection and stimulation of the crossed olivocochlear bundle (COCB) indicate further differences between CM and CR (D. C. Mountain, Ph.D. thesis, University of Wisconsin—Madison, 1978). Positive dc caused a relative augmentation of CM that grew with sound intensity, and a relative reduction in CR magnitude that decreased with intensity. Negative dc caused effects of similar magnitude but opposite sign. COCB stimulation caused enhancement of both CM and CR. Present models cannot account quantitatively for these results.

ISSN:0001-4966    

DOI:10.1121/1.384299

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

In the alligator lizard the entire basilar membrane is accessible for measurements of its velocity by the Mössbauer method. Tests of the method indicate (1) the Mössbauer source can be placed on the basilar membrane without altering the signal‐transmission properties of the cochlea, and (2) the source adheres to the basilar membrane. Isovelocity curves (IVCs) were constructed by plotting (as a function of tone frequency) the sound‐pressure level at the tympanic membrane required to produce a specified velocity amplitude. IVCs from 21 lizards for source locations spanning the length of the basilar membrane indicate that basilar‐membrane velocity doesnotvary systematically with longitudinal location as it does in mammalian cochleas. Measurements of velocity waveforms in two lizards do not indicate substantial nonlinearity in the inner‐ear mechanical system. The frequency dependence of the basilar‐membrane velocity is similar to that of the extrastapes velocity over the range 0.4 to 2 kHz. Thus, the tonotopic organization and frequency selectivity, which have been previously demonstrated in this species in responses of both auditory‐nerve fibers and cells of the receptor organ, are apparently not primarily determined by basilar‐membrane motion.

ISSN:0001-4966    

DOI:10.1121/1.384300

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Frequency discrimination was measured as a function of level for tones of 500, 1000, 2000, 3000, and 4000 Hz. The tones were masked by a wide‐band noise whose level was set to maintain constantE/No. Frequency discrimination was found to improve with level for tones of 500 and 1000 Hz while it grew worse for tones of 3000 and 4000 Hz. The data for 500 and 1000 Hz are accounted for by the periodicity‐type neural timing model of Green and Luce [’’Counting and Timing Mechanisms in Auditory Discrimination and Reaction Time,’’ inContemporaryDevelopmentsinMathematicalPsychology, edited by D. H. Krantz, R. C. Atkinson, R. D. Luce, and P. Suppres (Freeman, San Francisco, 1974), Vol. 2]. The data for 3000 and 4000 Hz are explained by the modified energy detection model of Henning [J. Acoust. Soc. Am. 42, 1325–1334 (1967b)].

ISSN:0001-4966    

DOI:10.1121/1.384301

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A simultaneous masking paradigm was employed to demonstrate that combination tones are ’’stimulus‐like’’ in nature. Three musically sophisticated listeners adjusted the level of pure tones at various frequencies to just mask a pulsing signal corresponding to a tone at 1200 Hz and 20 dB SPL. The signal was produced by four stimulus conditions: (1) a pulsing tone at 1200 Hz; (2) a combination tone at 2f1−f2=1200 Hz produced by a continuousf1at 1650 Hz and a pulsingf2at 2100 Hz; (3) a control for condition 2 with a pulsing tone at 1200 Hz and a continuousf1at 1650 Hz; and (4) a combination tone atf2−f1=1200 Hz produced by a continuousf1at 1900 Hz and a pulsingf2at 3100 Hz. Across subjects and stimulus conditions the shapes of the tuning curves were similar; whether for an externally presented single tone or a combination tone, minimum masker level (which corresponds to the tuning‐curve ’’tip,’’ the frequency at which masking is most effective) was always at frequencies near 1200 Hz. These findings are consistent with previous psychophysical as well as recent physiological evidence which indicates that, regardless of how generated, each of the combination tones 2f1−f2andf2−f1is present in the motion of the basilar membrane in the cochlear region around the characteristic place of the combination‐tone frequency.

ISSN:0001-4966    

DOI:10.1121/1.384302

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Psychophysical two‐tone suppression was measured in three normal‐hearing young adults using the pulsation‐threshold technique. The primary objective was to study the effect ofL1on psychophysical two‐tone suppression forf2/f1≳1.0. Measurements were obtained at low and mid frequencies and for input levels ranging from 40 through 85 dB SPL. Forf1=1000 or 2000 Hz, suppression increased initially withL1and then decreased forL1?55 to 70 dB SPL. Forf1=500 Hz, however, suppression increased monotonically throughout the range ofL1values examined. These findings are explained by assuming that forf1?1000 Hz the nonlinear mechanism responsible for two‐tone suppression is very susceptible to reversible dysfunction produced by the presentation of high‐intensity stimuli.

ISSN:0001-4966    

DOI:10.1121/1.384303

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Previous measurements have indicated that vowels before voiced and voiceless consonants exhibit a systematic duration difference, the former being longer approximately by a 3:2 ratio than the latter. Experiments with synthetic speech have shown that vowel duration is an important cue for the voicing distinction of the following consonant in word‐final position. In the present paper the role of this cue is evaluated for natural speech, which may also contain secondary cues for maintaining this distinction. The stimuli, spoken by a female speaker, were 24 English monosyllabic words ending with voiced stops, fricatives, and consonant clusters after intrinsically long and intrinsically short vowels. Duration of the vowel nucleus was systematically reduced using a digital gating technique. Recognition rates as a function of vowel duration were obtained. Category change takes place mainly for intrinsically long vowels and for high vowels in combination with final fricatives alone or in consonant clusters. In other cases, category change cannot be established even after the vowel duration is reduced to only 30% of its original duration. In particular, the presence of a long voice bar for a final voiced stop will make shortening of the vowel perceptually less effective. A multiple regression analysis of the experimental data indicates that in natural speech not only vowel duration, but also voice bar duration, duration of silent closure preceding the final release transient, and duration of the release burst or frication noise, depending on the consonant type, vary in weight as cues for voicing under different vowel‐ and consonant‐type conditions.

ISSN:0001-4966    

DOI:10.1121/1.384304

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Listeners were asked to identify ambiguous and unambiguous stop‐vowel targets placed in monotic and dichotic competition with second formants (bleats) from voiced consonant–vowel (CV) syllables lying along a place‐of‐articulation continuum. Target performance varied with bleat‐continuum position as well as bleat intensities. In cases where target errors occurred, either dichotically or monotically, they reflected predominantly the place cue of the bleat. This result, like that of previous studies, suggests the dominance of target or bleat reflects the relative ’’salience’’ of the two signals’ cues. Differences were seen between monotic and dichotic conditions in the rate of change in performance with bleat intensity and continuum position. The rate of monotic performance change was a more precipitous (higher slope) function of these variables than was dichotic performance. This difference was interpreted as suggesting that monotic interference includes a peripheral masking component which is sensitive to the relative spectral energies of target and bleat. Dichotic effects, in contrast, seem to primarily reflect the operation of (central) processes which grant different perceptual weights to signals’ cues depending on their intensity‐dependent saliences. The observation that ambiguity,perse, of the targets (or the CV’s from which the bleats were extracted) played little role in predicting results, was interpreted as reflecting a primarily prephonetic (i.e., auditory) locus for both monotic and dichotic interactions.

ISSN:0001-4966    

DOI:10.1121/1.384305

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP