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May 1978

Volume 63, Issue S1, pp. S1-S87

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back to top Session P. Physiological Acoustics I: Neurological Effects and Masking
Contributed Papers
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The effect of sensorineural hearing loss on acoustic stapedius reflex growth functions (A)

Shlomo Silman, Gerald R. Popelka, M. H. Miller, and Stanley A. Gelfand

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S42-S42 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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The growth function of the acoustic stapedius reflex was measured in subjects with normal hearing and sensorineural hearing loss of cochlear origin. The effects of age and magnitude of hearing loss were controlled. Activating stimuli were 500‐, 1000‐, and 2000‐Hz tones and broadband noise. Stapedius muscle activity was inferred from acoustic impedance measures in the contralateral ear. The mean growth functions were essentially linear in log‐log plots with the rate of growth equal for the two groups. The mean growth function for the noise signal was curvilinear for the normal‐hearing group and linear for the hearing‐loss group. Comparison of slope functions derived from the fitted data indicated that the normal rate of reflex growth for the noise signal, over a limited range above reflex threshold, increases in ears with cochlear lesions. For higher‐level noise signals, however, the normal rate of reflex growth is unchanged by these lesions. The effect of a cochlear lesion on the input‐output function of the cochlea for both tonal and noise stimuli is to maintain the rate of reflex growth but shift the function along the intensity axis by an amount equal to the shift in reflex threshold.
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A tympanometric evaluation of middle‐ear development in neonatal hamsters (A)

E. M. Relkin, J. C. Saunders, and D. F. Konkle

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S42-S43 (1978); (2 pages)

Online Publication Date: 11 Aug 2005

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Tympanometry was used to follow the maturation of middle‐ear function in neonatal hamsters from 6 to 80 days of age. Subjects in each of seven age groups were anesthetized, mounted in a head holder, and the tympanic ring and auditory bulla were exposed surgically. The bulla was ventilated with small bore nylon tubing in order to equalize middle‐ear pressure to ambient pressure. A tympanometer probe was sealed directly over the tympanic membrane using a short piece of rubber tubing to couple the probe to the tympanic ring. The magnitude of relative acoustic impedance was measured at frequencies between 1.0 and 1.5 kHz. Relative acoustic impedance was the difference between the impedance measured when the tympanic membrane was stressed with a pressure of +200 mm H2O and the minimum impedance that could be obtained as the pressure was reduced. There was no measurable impedance magnitude difference on day six, but by day 15 small though reliable values could be obtained. Thereafter, impedance magnitude changed rapidly and reached a plateau after 33 days. No further changes were noted in 77‐day‐old animals which were considered to be adults. Results will be discussed with regard to the maturation of middle‐ear morphology and inner‐ear physiology. [Supported in part by the NSF and the Deafness Research Foundation.]
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The effects of cholinesterase antagonists on stapedial reflex behavior (A)

R. A. Ruth, M. E. Johns, R. W. Cantrell, and L. D. Kramer

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S43-S43 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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We have studied acoustic reflex behavior in patients with myasthenia gravis. The underlying defect in this disorder is felt to be a reduction in the postsynaptic acetylcholine (Ach) receptor sites. The increasing weakness of these patients brought on by exercise is thought to be secondary to increased neuromuscular blockade. This affect can be reversed by anticholinesterase agents thereby increasing Ach/receptor ratios hence improving muscular response. At times these drugs can result in increased neuromuscular block if super saturation of the system is reached, i.e., a cholinergic response. The purpose of the present investigation was to evaluate the therapeutic and toxic effects of various anticholinesterase agents on acoustic reflex behavior in patients with a broad spectrum of neuromuscular blockade. Measurements included acoustic reflex threshold, reflex growth function, and fatigibility of the reflex response to both continuous and interrupted acoustic stimulation. In this large population (39) of myasthenic patients in varying stages of therapeutic control, we have observed the effects of edrophonium HCl on the acoustic reflex. We can divide these patients into two groups: those showing facilatory response (e.g., decreased threshold, increased magnitude and growth function, and decreased fatigue) and those exhibiting disintegration of response patterns (e.g., increased threshold or absent response, decreased magnitude and growth function, and increased fatigue).
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Cochlear insults from noise, drugs, and genetics (A)

D. B. Webster and M. Webster

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S43-S43 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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In recent years, cochlear damage has usually been documented by the loss of hair cells as judged from surface preparations; in some reports, small samples have also been taken for radial light or electron microscopic analyses. The present study used three groups of deaf guinea pigs: (1) deafened by kanamycin‐ethacrynic acid; (2) deafened by 159‐dB‐SPL noise; and (3) genetically deaf waltzing guinea pigs. Ears were studied by light microscopy, using serial paraffin sections cut in the plane of the modiolus. In all animals, there is more extensive damage to the organ of Corti than simple hair cell loss, and there is a secondary loss of spiral ganglion cells. Basilar membrane, tectorial membrane, Reissner's membrane, and stria vascularis are not affected. The time course for total organ of Corti loss and spiral ganglion loss is dependent upon the type of deafening but the end results are all similar. [Supported by NIH grants NS‐12510 and NS‐11647.]
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A physical model of basilar membrane dissipation (A)

Jont B. Allen

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S43-S43 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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In mechanical models of the cochlea it is very commonly assumed that the basilar membrane (BM) may be treated as a locally reactive impedance, namely that the pressure across the BM is proportional to the BM velocity. This impedance function typically contains three terms which may be identified as the BM stiffness K, BM mass M, and BM dissipation R. K and M have been directly measured and modeled. The damping term R, however, has remained unexplained from both an experimental and a theoretical point of view. We will present a theory of damping in the cochlea that appears to be consistent with known cochlear morphology and with other known bits of relevant information, (i.e., damping as determined by modeling). Finally, we will discuss a possible mechanism which would allow R to be signal level dependent (nonlinear mechanics) as discussed by D. O. Kim and C. Molnar [The Nervous System (Raven, New York, 1975); J. L. Hall, J. Acoust. Soc. Am. 61, 802–810 (1977).]
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The tectorial membrane may sharpen the cochlear frequency selectivity (A)

J. J. Zwislocki and E. J. Kletsky

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S43-S43 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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Radial shearing motion between the tectorial membrane and the reticular lamina is generally held responsible for the excitation of the hair cells. However, the shearing motion must depend on the coupling between the tectorial membrane and the organ of Corti. A sufficiently tight coupling would effectively prevent it. Motion of one part of the tectorial membrane must also depend on the motion of the adjacent parts because of a longitudinal coupling within the membrane. When the membrane is driven by the organ of Corti in the same direction over a substantial length, it should be entrained more than when neighboring sections are driven in opposite directions. Consequently, the shear relative to the reticular lamina should be minimized where the cochlear waves are long and maximized where they are short. Since the wavelength is the smallest near the vibration maximum, the shear should be the greatest there. A computer simulation shows that such a mechanism can account for the difference between the known neural and basilar membrane tuning curves. [Work supported by NIH.]
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The effect of DC polarization on the magnitude and phase of the CM harmonics (A)

D. C. Mountain, A. E. Hubbard, and C. D. Geisler

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S43-S44 (1978); (2 pages)

Online Publication Date: 11 Aug 2005

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Rectification processes must play an important role in the mechanical to neural transduction process in the auditory system since intracellular recording has demonstrated large DC receptor potentials for sinusoidal acoustic stimuli in inner haircells [I. J. Russell, and P. M. Sellick, Nature 267, 858–860 (1977)]. Any rectification process would not only generate DC potentials but also would generate even harmonic distortion. The magnitude and phase of the CM fundamental and harmonics were measured in scale media of the first turn of the guinea pig cochlea using digital signal‐processing techniques. The data suggest that the even order harmonics are the sum of two separate components which are 180° out of phase at low acoustic frequencies. One component dominates at low SPL and the other at high SPL. Positive DC polarization shifts the transition of the two components to lower SPL and a reverse current shifts the transition to higher SPL. The results are consistent with our recent hypothesis that the haircell membrane resistance is nonlinear. [This research was supported by the National Institutes of Health.]
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Some vascular effects of noise exposure in the chinchilla (A)

A. Axelsson, D. Vertes, and D. M. Lipscomb

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S44-S44 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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Chinchillas were exposed to pink noise at levels ranging from 110 dB (for 8 h) to 125 dB (for ¼ h). After a three‐week survival period, the animals were terminated without anesthesia and tissues were prepared using a soft‐surface preparation technique [Axelsson et al., Ann. Otol. 83, 537 (1974)]. Cochlear hair cell damage as well as vascular pathology was slight. On occasion, a vessel or vessel segment was obviously atypical, thus allowing noise‐exposed animals to be differentiated from their non‐noise‐exposed controls. More often, however, differences between animals were more discrete and only evident through a computer analysis of the data. The specific effects of these particular noise‐exposure parameters on the cochlear blood supply of the chinchilla will be discussed.
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Unmasking effects produced by combination tones (A)

Richard S. Tyler, Arnold M. Small, and Paul J. Abbas

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S44-S44 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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This experiment investigates some interactions between combination tones and suppression. Using a two‐tone stimulus in a psychophysical forward‐masking paradigm, the effective masking of the first tone (masker) on the signal can be reduced by the addition of a second tone (suppressor). We present evidence here that a combination tone, not present in the stimulus, can effectively be used as a suppressor. By comparing the threshold shift produced by the masker alone and by the masker‐suppressor combinations, the amount of unmasking (or suppression) as a function of suppressor frequency was measured. Then, two higher‐frequency stimuli were added to the masker, neither of which produced unmasking when presented individually. When the cubic difference tone or the difference tone produced by these two additional stimuli were of appropriate frequency, unmasking was observed. The unmasking produced by the combination tones was similar in its frequency characteristics to that of a single suppressor tone. The results suggest that both the cubic difference tone and the difference tone behave as if they were present in the stimulus.
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Intensity effects in forward masking: Implications for psychophysical tuning curves (A)

Gregory P. Widin and Neal F. Viemeister

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S44-S44 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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The effects of masker intensity and masker frequency on the threshold of a 1‐kHz, 20‐ms probe were assessed in forward masking, with a masker‐probe delay of 5 ms. In general, probe threshold is a power function of masker intensity, with an exponent considerably less than unity; the exponent and constant of proportionality depend upon masker frequency. For example, with a 1‐kHz masker, a 10‐dB increase in masker level increases probe threshold by only about 5 dB, over a 60‐dB range of masker intensities. The nonlinear relation between probe threshold and masker intensity is consistent with the increased “selectivity” sometimes observed in forward‐masked tuning curves as compared with those obtained in simultaneous masking. These data then emphasize the importance of nonlinear intensity effects, in addition to possible changes in true frequency selectivity, in determining the form of psychophysical tuning curves obtained in forward masking and their relation to those obtained in simultaneous masking. [Supported by NICHD, NINCDS.]
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Temporal cueing effects in backward change masking (A)

R. E. Pastore and M. L. Barnett

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S44-S44 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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In a simple monaural yes‐no paradigm observers were asked to detect a 20‐ms segment of a 3000‐Hz sinusoid under two types of masking conditions both with and without contralateral temporal cues. Backward change masking was produced by a postsignal change in the frequency centroid of the masking noise in which both spectrum level of the noise within the critical band of the signal and its total power remained constant. The change masking was produced by an alternation between two masking noises which were classified as “high” and “low,” corresponding to the perceived pitch of each. Relative to the continuous (no change) conditions, results show a differential masking effect from backward change masking out to a 300‐ms delay between signal offset and change onset in the noncued experimental conditions. A timing cue was then provided by a gap in an otherwise continuous, uncorrelated noise in the contralateral ear. The gap cue led the signal by 5 ms and was switched off simultaneously with signal offset. Results show the cue to be effective in reducing backward change masking, thus implicate temporal uncertainty as a factor in backward change masking. These results parallel those reported at previous meetings for standard backward masking conditions [J. S. Puleo and R. E. Pastore, J. Acoust. Soc. Am. 60, S49(A) (1976)]. [Research supported by a grant from NINCDS.]
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Measurement of suppression in a simultaneous masking paradigm (A)

Walt Jesteadt and Eric Javel

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S44-S44 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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Houtgast [Acustica 30, 214–221 (1974)] compared the partial masking, or reduction in loudness, of a tone produced by the addition of noise to the suppression of the tone by the noise, as measured in pulsation‐threshold and forward‐masking paradigms. Because the effective level of the tone was reduced by similar amounts in both cases, Houtgast suggested that both phenomena may reflect the same underlying mechanism. As a further test of this hypothesis, we have measured the effective level of probe tones of various frequencies and intensities in the presence of band pass and high‐pass noises. The effective level of the probe tone is defined as the level of a contralateral tone presented in quiet that is required to produce a centered image. For tones below the cutoff of a high‐pass noise, partial masking is relatively independent of probe‐tone intensity, for intensities less than 75 dB SPL. The data are similar in this respect to two‐tone suppression data for single auditory nerve fibers described by Javel, Geisler, and Ravindran [J. Acoust. Soc. Am. 63, (1978), in press]. [Supported by NIH.]
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Psychoacoustical tuning curves and narrow‐band masking in normal and impaired hearing (A)

Mary Florentine

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S44-S45 (1978); (2 pages)

Online Publication Date: 11 Aug 2005

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Psychoacoustical tuning curves and narrow‐band masking were measured in normal and groups of moderately hearing‐impaired observers (conductive, otosclerosis, noise‐induced, and degenerative). The SPL of pure tones needed to just mask an intermittent 4‐kHz tone at 10 dB SL was measured as a function of the masker's frequency. Results support Schorn, Wurzer, Zollner, and Zwicker [Laryngol. Rhinol. 56, 121 –127 (1977)] and show wider tuning curves for the noise‐induced and degenerative groups than for the other groups. In the same observers, thresholds for 600‐ms pure tones were measured as a function of frequency in the presence and absence of a continuous 40‐dB‐SL narrow‐band noise centered at 4 kHz. Results show an enlarged upward spread of masking only for the noise induced and degenerative groups. However, at equal SPL the differences between observers with normal hearing and those with cochlear impairment were considerably reduced. [Work supported by Rotary Foundation and Deutsche Forshungsgemeinschaft through Sonderforschungsbereich 50 “Kybernetik,” Munchen.]
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