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Nov 1982

Volume 72, Issue S1, pp. S1-S108

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back to top Session D. Physiological Acoustics I: Peripheral Acoustics and Physiology
Contributed Papers
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The influence of the sound level of a steady‐state broadband noise on the temporal response of the acoustic reflex (A)

Nicole Lalande and Raymond Hétu

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S6-S6 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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The influence of the sound level of a steady‐state pink noise on the short‐ and the long‐term response of the contralateral acoustic reflex was investigated with nine adult subjects. Three noise levels were selected (LpA of 95, 100, and 110) for a duration of 16 min (or 8 min occasionally). Based on previous data [R. H. Wilson et al., J. Acoust. Soc. Am. 64, 782–791 (1978)], it was hypothesized that when the reflex activity is expressed in absolute value of change in acoustic susceptance, the reflex decay is the same whatever the intensity of the noise; expressed in relative value of percentage of change in susceptance, the reflex adaptation is greater for a low level of noise than for higher ones. Results clearly confirmed the above hypothesis. These findings explain the conflicting results previously obtained in terms of the way data are analyzed. Practical implications concerning the protection afforded by the acoustic reflex under such noise exposures will be discussed.
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The importance of external and middle ear contributions to bone conduction in man (A)

S. Gatehouse

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S6-S6 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Differences between air conduction (a–c) and bone conduction (b–c) thresholds are commonly used to determine the presence and magnitude of a middle ear abnormality in the human audiotory system, making the tacit assumption that b–c directly stimulates the cochlea. Animal experiments have long established that b–c transmission is a complex phenomenon [J. Tonndorf, in Foundations of Modern Auditory Theory, Vol. 2 (Academic, New York, 1972)] with significant contributions from middle and external ear components. An artificial reversible middle ear abnormality may be induced in man by maintaining an air pressure in the external meatus. The shifts in a–c and b–c thresholds provide a means to evaluate the relative importance of the external and middle ear components. At the lower frequencies of 250 and 500 Hz, these components predominate; at 500 Hz there is an a–c shift of 15.9 dB accompanied by a b–c shift of 15.8 dB. These results have important implications for the interpretation of air and bone conduction thresholds.
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Ear‐canal resonances and the assessment of hearing thresholds at high frequencies (A)

K. N. Stevens, S. H. Blumenthal, D. M. Green, and M. Krasner

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S6-S6 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Standing waves in the ear canal cause substantial difficulties in the assessment of high‐frequency (8000–20 000 Hz) hearing thresholds because of uncertainties in the specification of the acoustic stimulus. A calibration procedure is proposed for estimating the sound prcssure p1 at the inner end of the ear canal by measuring the poles of the impulse response at the entrance to the ear canal when an acoustic source is coupled directly to the canal through a short tube. This calculation is based on the fact that the transfer function from the source to p1 is an all‐pole function. As a step towards implementation of this procedure, frequencies and bandwidths of ear‐canal resonances for a number of ears have been measured. The data show that these resonances have bandwidths as small as 300 Hz, and deviations from equal spacing that are usually no greater than 10%. The pressure p1 has been calculated from the appropriate all‐pole transfer function, and shows systematic and predictable differences with measured peak sound pressures in the outer 1 to 1.5 cm of the ear canal, as expected on the basis of measurements with models. [Supported by a contract from NINCDS.]
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Electrical stimulation of the auditory nerve: Membrane models applied to the interpretation of electrophysiological and psychophysical responses (A)

M. White and M. Merzenich

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S6-S6 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Electrophysiological and psychophysical measures of threshold as a function of sinusoidal stimulus frequency deviate considerably from those predicted by Hill's membrane model. Using a modified Hodgkin‐Huxley model, considerably better estimates of threshold were obtained over the frequency ranges investigated. The Hodgkin‐Huxley model was modified by increasing the sodium inactivation rate constant, beta‐h, by a factor of four. This model has been useful in interpreting electrophysiological and psychophysical responses to a range of pulse and sinusoidal stimuli. [Work supported by NIH.]
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Ear‐canal acoustic emissions as frequency‐specific indicators of cochlear function (A)

Richard A. Schmiedt and Cheryl L. Addy

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S6-S6 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Acoustic emissions in the form of distortion products (2f1‐f2) can be measured in the external ear canal. Previous work has shown that the nonlinearities generating these emissions reside in the cochlea and disappear with metabolic disruption. Distortion products measured in the cochlear microphonic and in the responses of auditory‐nerve fibers have been shown to be generated largely at the cochlear location associated with the primary tones. If cochlear emissions behave similarly, it should be possible to generate an “acoustic‐emission audiogram” with appropriately placed primary pairs; i.e., low‐frequency pairs could be used to test the cochlear apex, high‐frequency pairs to test the base. We have obtained acoustic‐emission and whole‐nerve action potential audiograms in Mongolian gerbils and cats both before and after exposure to narrow‐band noise sufficient to cause a temporary threshold shift. Our results indicate that emssions produced by lower‐level primaries (70 db SPL) seem to reflect the recovery of the whole‐nerve response over time better than higher‐level primaries (80 dB SPL). Further, acoustic emissions can be used on a frequency‐specific basis to monitor the condition of the mid and basal regions of the cochlea. [Work supported in part by a South Carolina Biomedical Research Grant.]
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Acoustic and auditory nerve measurements of distortion products (A)

P. F. Fahey and J. B. Allen

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S6-S7 (1982); (2 pages)

Online Publication Date: 12 Aug 2005

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We have made measurements of distortion products responses in the ear canal and in the auditory nerve of the cat. The frequencies and levels of the primaries, f1 and f2, were varied in such a way that the frequency and level of the distortion product, as measured by the response of a neuron at its threshold, were held constant. In particular, we found, as has been previously reported by others, that the amplitude of the primaries needed to give an isoresponse was relatively independent of frequency for the f2‐f1 signal and strongly frequency dependent for the 2f1‐2f2 signal. The level and frequency dependence of the distortion product 2f1‐f2 as measured in the ear canal (which were not seen when the driver was terminated with an acoustic cavity) seem to agree with the level and frequency dependence of the distortion products that were detected by single neurons in the auditory nerve.
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Phase and group delay in the auditory nerve relative to the cochlear microphonic (A)

J. B. Allen

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S7-S7 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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We have extended our earlier measurements of cochlear phase response by measuring the round window potential phase, which is then used as a reference phase. This normalization greatly simplifies the phase and group delay because it appears to remove middle ear artifacts. After being normalized, the group delay shows a monotonically increasing delay with increasing frequency. This data seems to be inconsistent with a large class of “second filters.”
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Extensions of Davis' hair cell model (A)

J. B. Allen

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S7-S7 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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By making a very simple modification to the Davis model of hair cell transduction, it is possible to accurately model neural period histogram data. The model data match the neural data over the entire range of experimental observations. Computed responses to pure tones and to tone bursts will be compared to experimental observations.
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Coding of auditory information in pigeon vestibular nerve fibers (A)

H. P. Wit and J. D. Bleeker

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S7-S7 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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After fenestration of the lateral semicircular canal of the pigeon auditory stimuli (e.g., tone bursts) evoke phase‐locked responses in the vestibular nerve. Single unit activity was measured in the ampullary branch of the vestibular nerve innervating the crista in the horizontal semicircular duct. The sound stimulus was delivered to the eardrum of the pigeon through a silastic tube. Most units show best phase lock for frequencies of about 700 Hz. Few units however seem to be “tuned” to lower frequencies. The lowest sound pressure level that has an observable influence upon the firing pattern of a unit is about 95 dB SPL at the units best frequency. The low‐frequency slope of the tuning curve for a unit (sound pressure level versus stimulus frequency for a present synchronisation criterion) is approx. 18 dB/oct. The high‐frequency slope is 25 dB/oct. If the roof of the membranous ampulla wall is directly stimulated with a piezoelectric vibrator, tuning of most fibers is not different from the tuning measured with stimulation by (sound) pressure variations in the ear canal. This rules out the middle ear system of the pigeon as the primary source for the observed tuning. The threshold for observable phase lock in direct stimulation is a vibrator amplitude of 20 nm, corresponding to a velocity of 0.1 mm/s at 700 Hz.
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Effects of stimulating frequency on discharge patterns of single eighth nerve fibers in the bullfrog (A)

Andrea L. Megela

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S7-S7 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Temporal discharge patterns to tone bursts at best excitatory frequency (BEF) have been examined in single eighth nerve fibers of many vertebrates. There are few descriptions, however, of how discharge patterns may vary in response to tone bursts at other frequencies within a fiber's excitatory tuning curve. Discharge patterns of single eighth nerve fibers in the bullfrog were studied in response to tone bursts at BEF, and at those frequencies representing upper and lower flanks of the tuning curve at 10 and 20 dB above threshold. High‐frequency‐sensitive fibers innervating the basilar papilla showed no changes in their discharge patterns, analyzed as PST histograms, with stimulating frequency. For these fibers, the shape of the PST histogram at BEF provides a good prediction of the histogram shape at frequencies at the tuning curve flanks. On the other hand, the discharge patterns of low‐frequency‐sensitive fibers innervating the amphibian papilla varied with stimulating frequency, from a more sustained mode of firing at BEF to a more phasic mode of firing above BEF. Thus, the discharge patterns of amphibian papilla fibers show more variability with stimulating frequency than do those of basilar papilla fibers. [Supported by NIH grant NS09244 to R. R. Capranica.]
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Responses of cerebellar units to acoustic stimuli in the CF‐FM bats, Pteronotus parnellii parnellii and Pteronotus parnellii rubiginosus (A)

Philip H.‐S. Jen, Xinde Sun, and Tsutomu Kamada

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S7-S7 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Single units which faithfully fired action potentials to pure tones (35 ms in duration and 0.5 ms rise and decay times) could be recorded from the cerebellar vermis and hemispheres of the CF‐FM bats, Pteronotus parnellii parnellii and Pteronotus parnellii rubiginosus. Most units were recorded at a depth less than 1000 μm from the brain surface and they fired less than five impulses to acoustic stimuli. Only a few units fired tonically to acoustic stimuli. Off responses could be recorded from those units with best frequencies tuned at around 61 kHz which is the predominant CF component of the bat's echolocative signals and Doppler‐shifted echoes. Response latencies of these units were between 1.5 and 27 ms and minimum thresholds were between 2 and 83.5 dB SPL. While most of the threshold curves of these units were either broad or irregular, those curves with best frequencies tuned at around 61 kHz were extremely sharp. The highest Q10‐dB value obtained from the sharply tuned threshold curves was 153. These data indicate that auditory specialization for processing of species‐specific echolocative signals also exists in the cerebellum of the CF‐FM bat. [Work supported by NSF BNS 80‐07348 and USPH 1‐K04‐NS‐00433‐03 to P. Jen.]
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Auditory physiological properties of the units in the cerebellum of the FM bats, Eptesicus fuscus and Myotis lucifugus (A)

Philip H.‐S. Jen, Tsutomu Kamada, and Xinde Sun

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S7-S7 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Response properties of cerebellar units in the FM bats, Eptesicus fuscus and Myotis lucifugus were studied under free‐field and closed‐system sound stimulation. Units responding to sound stimuli could be isolated from a rather large area of cerebellar vermis and the cerebellar hemispheres. Only a few units fired tonically while most discharged between one and five impulses during acoustic stimulation. Response latencies ranged between 2.97 and 68 ms with most between 8 and 14 ms. Threshold curves were broadly tuned with a triangular or irregular shape. Similar to units in the auditory nuclei, the number of impulses fired by cerebellar units changed either monotonically or non‐monotonically with stimulus intensity. In the closed system study, the latency of an investigated unit to monaural stimulation was approximately the same as to binaural stimulation. Threshold curves of the same unit measured from each ear were also similar in shape and best frequency. Although all the units studied could be activated by stimuli delivered to either ear, the neural mechanism of binaural interaction is not a simple summation or occlusion. [Work supported by NSF BNS 80‐07348 and USPH 1‐K04‐NS‐00433‐03 to P. Jen.]
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