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Nov 1981

Volume 70, Issue S1, pp. S1-S109

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back to top Session QQ. Physiological Acoustics VI: Symposium in Honor of E. Glen Wever—Comparative Studies of the Terrestrial Ear. II
Contributed Papers
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Tympanic and extratympanic sound transmission in the leopard frog, Rana pipiens (A)

Walter Wilczynski, Carl Resler, and Robert R. Capranica

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S93-S93 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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The relative efficiency of sound transmission to the inner ear of the leopard frog by tympanic vibration and by extratympanic stimulation (presumably via tissue conduction) was investigated by recording the thresholds of eighth nerve auditory fibers at various frequencies within their excitatory tuning curves. The animals were placed on a vibration‐isolating table. The eighth cranial nerve was exposed through the roof of the mouth, and a clay cap, molded to mimic the mouth spaces into which the eustachian tubes open, was inserted and sealed with silicon grease, leaving the surgical exposure accessible. An earphone was sealed around one tympanum; the contralateral tympanum and external nares were covered with grease. A loudspeaker was placed 0.8 m from the frog for free‐field stimulation. Thresholds of single eighth nerve fibers to sound presented alternately through the earphone and through the loudspeaker were compared. For frequencies below 0.9 kHz, thresholds for the two modes of stimulation were comparable, and generally within 5 dB. For higher frequencies, threshold separation was greater: at 1.7–2.0 kHz, thresholds to sounds presented via the speaker were 15–20 dB higher than those presented through the earphone. These results suggest that at low frequencies the frog's inner ear can be stimulated by both tympanic vibration and by a nontympanic mechanism with nearly equal sensitivity. [Supported by NIH 06237 and NSF BNS 7706803.]
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Biophysics of underwater hearing in Rana catesbeiana (A)

Thomas E. Hetherington and R. Eric Lombard

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S94-S94 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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A vertical, water‐filled steel pipe, 3 m long with 0.63‐cm‐thick walls and 15‐cm internal diameter was used to determine the biophysical basis of underwater hearing sensitivity in Rana catesbeiana. A speaker inside the base produced standing waves. Pressure and particle motion were measured with a hydrophone and geophone, respectively, and were 90° out of phase along the length of the tube. Microphonic responses were recorded from the inner ear of frogs lowered through pressure and particle motion maxima and minima. The air‐filled lungs of whole frogs produced distortions of the sound field. Preparations of heads with only an air‐filled middle ear produced little distortion and showed clear pressure tracking at sound intensities 10–20 dB above hearing thresholds from 0.2 to 3.0 kHz. Filling the middle ear with water decreased or abolished microphonic responses. Severing the stapes reduced responses except at certain frequencies below about 1 kHz which varied with body size and likely represent resonant frequencies of the middle ear cavity. We conclude that Rana catesbeiana responds to underwater sound pressure from about 0.2 to 3.0 kHz with the middle ear cavity responsible for pressure transduction. [Work supported by NSF and NIH.]
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Cetacean middle and inner ear morphology (A)

Jeffrey C. Norris

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S94-S94 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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Middle and inner ear structure and function of seven Odontoceti; Tursiops truncatus, Delphinus delphis, Grampus griseus, Globicephela sp., Orcinus orca, Phocoena phocoena, Phocoenoides dalli, and four Mysticeti; Balaenoptera physalus, B. acutorostrata, Balaeana glacialis, and B. mysticetus were investigated. Measured parameters of middle ear morphology include ossicular mass, density, morphology, and lever ratios, tympanic membrane area, and calculations of middle ear impedances. The inner ear structures described and measured include cochlear morphology, basilar membrane length, width, and thickness, and spiral laminae morphology. Correlations are made between basilar membrane length, width, thickness and thickness/width. Greenwood's equations [D. D. Greenwood, J. Acoust. Soc. Am. 33, 1344–1356 (1961)] are used to estimate auditory thresholds using basilar membrane length and elasticity. Verification of this procedure's accuracy is presented. Inner ear examinations were made using surface preparations, cross sectioning, and scanning electron microscopy. These investigations are designed to complement previous studies in other marine mammals and bats. Results are discussed in light of currently accepted cetacean auditory theory with special attention given to low‐frequency auditory adaptations in Mysticeti, high‐frequency hearing in phocoenids, and ossicular chain function.
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Efferent desensitization of the responses of turtle single auditory nerve fibers (A)

J. J. Art, A. C. Crawford, R. Fettiplace, and P. A. Fuchs

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S94-S94 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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Extracellular recordings were made from single auditory afferents and frequency‐threshold curves determined in the isolated half‐head of Pseudemys scripta. Constant current shocks, 20–500 μA, in trains at 250 s1, delivered at the junction between the anterior and posterior roots of the statoacoustic nerve, resulted in a prolonged elevation of the thresholds to pure tones, and a broadening of the frequency‐threshold curves of the auditory afferents. As an example, in one sharply tuned afferent, a threshold elevation of 41 dB at the characteristic frequency (CF, 700 Hz) was accompanied by a reduction in Q10 dB from 4.7 to 0.9. The extent of desensitization increased steeply with number of shocks, and a train of seven shocks could elevate the threshold at the CF by 80 dB. The desensitization could be demonstrated in a majority of recordings, and observed in the absence of antidromic firing of the afferent. We suggest that a component of this efferent effect may result from a detuning of the hair cell's electrical filter [A. C. Crawford and R. Fettiplace, J. Physiol. 312, 377–412 (1981)].
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Neural correletes of masked threshold (A)

Richard R. Fay and Sheryl Coombs

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S94-S94 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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The detectability of tonal and noise signals was measured in the goldfish using classical respiratory conditioning at various levels of a continuous broadband noise masker, and as a function of signal duration. At threshold for an 800‐Hz tone, the signal‐to‐noise ratio (E/N0 = 22 dB and is generally independent of noise level and signal duration. The response of single eighth nerve fibers of the goldfish was measured under identical acoustic conditions and at the same N0 levels used in the psychophysical studies. For E/N0 below 22 dB, phase‐locking to the signal occurs, but spike rate is not different from that evoked by noise alone. At E/N0 = 22 dB, the coefficient of synchronization tends to equal 0.5, and spike rate begins to rise above that evoked by noise alone. For E/N0 above 22 dB, synchronization begins to saturate and log spike rate grows linearly with signal level in dB. This function reaches a maximum slope of a doubling of driven rate per 3 dB increase in signal level under optimum conditions. Near E/N0 = 22 dB, the number of spikes evoked by a tone burst signal is linearly related to signal energy. While we are not able to determine whether masked signal detection is based upon synchronization or spike rate criteria, it is clear that behavioral detection is not based on synchronization values below 0.5.
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Neurophysiological measurements of temporal discrimination in an anuran amphibian (A)

Cynthia M. Hillery

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S94-S94 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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Two experiments to assess the ability of midbrain neurons in Hyla chrysoscelis to encode the temporal structure of acoustic stimuli were performed. A fast component of the average evoked potential (AEP), measured as a peak‐peak potential, provided a quantitative measure of rapid, synchronized activity in neuron subpopulations. (1) Using amplitude modulated sound stimuli, the just detectable depth of modulation as a function of modulation frequency was determined and produced neural modulation detection functions which showed bandpass characteristics with best modulation frequency between 60–200 Hz. Modulation depths between 100%‐6% were clearly detectable by the animals. (2) The masking effects of broadband noise on the response to a train of pure‐tone pulses was examined. The dynamic range of masking (AEP amplitude versus noise spectrum level) ranged from 20–30 dB. From these measures the CR band for the population of neurons sampled can be determined. Identical measurements were performed using the whole nerve action potential recorded from the eighth nerve in this species. Differential ability to encode temporal structure of acoustic stimuli peripherally and centrally was examined.
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Auditory responses in a vocal nucleus of the leopard frog Rana pipiens: Characterization and effects of hormones (A)

Peter G. Aitken and Robert R. Capranica

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S94-S95 (1981); (2 pages)

Online Publication Date: 12 Aug 2005

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Auditory‐evoked responses of single neurons were studied in the pretrigeminal nucleus of leopard frogs; this nucleus is involved in the control of vocal output [R. S. Schmidt, J. Comp. Physiol. 108, 99–113 (1976)]. Frogs receiving hormone treatment (human chorionic gonadotropin, 25 u subcutaneously daily for 5 to 14 days) and untreated frogs were used. There was a significantly greater probability (chi‐squared = 9.66, df = 1, p < 0.01) of encountering auditory activity in this nucleus in hormone‐treated frogs, but there was no apparent difference between the groups in the characteristics of the evoked activity. Most units showed V‐shaped tuning curves with best excitatory frequencies ranging from 350–1100 Hz, thresholds from 31–87 dB SPL, and Q(10 dB) from 1.2–5.1. Response latencies varied from 10–50 ms and dynamic ranges from 20–40 dB. Both phasic and tonic response patterns were seen. Approximately 10% of the units would not respond to pure tones except at intensities above 100 dB; these units would respond to white noise, with thresholds between 50 and 70 dB SPL. This auditory input to the vocal system may play a role in acoustically evoked mate calling. [Supported by N.I.H.]
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Orientation signals and responses of inferior collicular units to acoustic stimuli in certain FM and CF‐FM paleotropical bats (A)

Philip H.‐S. Jen and Roderick A. Suthers

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S95-S95 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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The echolocation system of six species of paleotropical bats was studied by recording their orientation signals and studying the electrophysiological properties of their inferior colliculus. The FM hats use short signals with frequency sweeping downward and the CF‐FM bats use signals consisting of a constant frequency followed with a brief downward frequency sweep. Most collicular units discharged either tonically or phasically with peak latency ranging from 3.5 to 49.5 ms. Their threshold curves were triangular shape with minimum thresholds ranging between 1.3 and 179. Sharply tuned threshold curves with very high Q10dB values were only obtained from collicular units of CF‐FM bats. An off response upon cessation of stimulus could be measured when the stimulus frequency was at the predominant CF. Whereas collicular units of FM bats were sensitive throughout the frequency range of their emitted signals, collicular units of the CF‐FM bats were much sharply tuned to a narrow band of frequencies near that of the CF component of orientation signals. [Work supported by NSF BNS 79‐13968.]
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Selectivity of single units in the central auditory system of the leopard frog to AM signals (A)

Gary Rose and Robert R. Capranica

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S95-S95 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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Single units in the auditory midbrain nucleus (torus semicircularis) were recorded in leopard frogs Rana pipiens. Acoustic stimuli consisted of pure tones, sinusoidal amplitude‐modulated (AM) tones, or sinusoidal amplitude‐modulated white noise. On the basis of iso‐intensity curves (sound pressure level is held constant while the rate of amplitude modulation is varied), the temporal selectivity of cells in the torus fall into four categories: Nonselective (response is independent of rate of AM); low‐pass (response is greatest to low rates of AM); high‐pass (response is greatest to high rates of AM); and tuned (response is best to a particular rate of AM). For both amplitude modulated tones and amplitude modulated noise the predominant response type is the tuned class. By using white noise as the carrier source, spectral factors can be eliminated as a source of tuning so that the selectivity of these cells is due exclusively to the temporal features of the stimulus. Those units which show temporal tuning respond maximally when the degree of modulation is 100%. Thus a “temporal tuning curve” could be constructed by determining, for various rates of AM, the percentage modulation required to give a criterion (threshold) number of spikes. The rate of AM at which this criterion threshold could be reached using the lowest percentage modulation is considered to be the best rate of amplitude modulation for that unit. [Supported by NINCDS grant NS‐09244.]
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Tonotopic and anatomical organization of inferior colliculus in the mustache bat, Pteronotus p. parnellii (A)

J. M. Zook, R. D. Bodenhamer, and G. D. Pollak

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S95-S95 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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This study combined single‐unit recording with electrophoretic deposits of Alcian Blue and horseradish peroxidase. Within the central nucleus of the inferior colliculus we find three physiologically distinct regions which are closely correlated with three cytoarchitectonically defined divisions. The anterolateral division contains units with low best frequencies (18 to 60 kHz). This area has a clear laminar organization of cells and dendrites visible in either Nissl‐stained or Golgi sections cut in the horizontal plane. Laminae sheets extend medial‐lateral while the tonotopic organization runs perpendicular to these sheets from high posterodorsal to low anteroventral. The medial division contains units with high best frequencies (62–114 kHz). This region is posteromedial to the anteriolateral division and lacks a clear laminar organization. The dorsal division contains only units with best frequencies in a narrow range around 61–62 kHz. This division occupies more than one‐third of the entire inferior colliculus and lies mainly dorsal and posterior to the anterolateral division. It lacks a clear laminar organization and can be distinguished from the medial division by cell size and packing density.
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Frequency representation and discharge properties of single units in the inferior colliculus of the mustache bat, Pteronotus parnellii (A)

G. D. Pollak, R. Bodenhamer, and J. Zook

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S95-S96 (1981); (2 pages)

Online Publication Date: 12 Aug 2005

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The biosonar signals of the mustache bat are characterized by a relatively long duration constant frequency (CF) component having a frequency of about 61 kHz, and a brief, downward sweeping frequency modulated portion. In this study we monitored the activity of neurons in the bat's inferior colliculus (IC), directing special attention to the distribution of best frequencies (BF), and the manner in which different BFs are organized within the nucleus. Remarkably, over 50% of the neurons in each bat's IC had almost identical FBs, the variation being only ±150–250 Hz. The frequency that these neurons were tuned to was about 61 kHz, and was the same frequency as that to which the individual bat's cochlear microphonic audiogram was also tuned. Neurons in this over‐represented frequency band were distinguished by their very sharp tuning curves, in which the average Q10 dB value was 122, and by the ability to respond to sinusoidally frequency modulated signals with spike trains in tight registry with the phase of the modulating waveform. The sinusoidally frequency modulated signals were designed to mimic the frequency modulations imposed upon the echo CF component by the beating wings of a small insect. These over‐represented neurons, having common BFs, common tuning properties, and sharing the ability to phase lock to frequency modulated signals, were found only in the posterior division of the IC, a region that is topographically and cytoarchitecturally segregated from the other divisions of the central nucleus of the bat's IC. [Supported by NIH Grants NS 13276 and NS 00367.]
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Vertical localization of sonar targets by the echolocating bat, Eptesicus fuscus (A)

Beatrice D. Lawrence and James A. Simmons

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S96-S96 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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Echolocating bats (Eptesicus fuscus) can discriminate between pairs of horizontal rods separated by different vertical angles with an acuity of 3° of arc. When the tragus, a prominent external‐ear structure located in front of the pinna and external‐ear canal, is deflected, vertical‐angle discrimination is very poor. The tragus acts as a reflector for producing secondary echoes in the.external‐ear impulse response. Vertical target direction is encoded acoustically by the timing and strength of these secondary reflections within the external ear relative to the sound arriving directly at the external‐ear canal. These reflections occur only 10 to 20 μs apart, but previous experiments have established that Eptesicus can perceive an echo's arrival time with an acuity of less than 1 μs and can distinguish as discrete echoes signals that are separated by such small time intervals. It thus appears as though echo timing is involved in perception of target range, shape, horizontal direction, and, now, vertical direction. [Work supported by NSF.]
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