Directional Hearing in the Japanese Quail (Coturnix Coturnix Japonica): II. Cochlear Physiology

The directional sensitivity of cochlear microphonics (CM) was studied inthe quail by rotating a free-field sound source (pure tones, 160-10 kHz)through 360° in the horizontal plane, under anechoic conditions. Sound diffraction by the head was monitored simultaneously by a microphone at the entrance to the ipsilateral (recorded) ear canal. Pressure-field fluctuations measured by the microphone were non-directional (≤ 4 dB) up to 4 kHz; the maximum head shadow was 8 dB at 6.3 kHz. In comparison, the CM sensitivity under went directional fluctuations ranging up to 25 dB for certain low, mid and high frequency band widths. There was noticeable variation between quail for frequencies producing maximum directional effects, although consistently poor directionality was seen near 820 Hz andto a lesser extent near 3.5 kHz. Well-defined CM directivity patterns reflected the presence of nulls (insensitive regions) at critical positions around the head and the number of nulls increased with frequency. Five major types of directivity patterns were defined using polar co-ordinates: cardioid, supercardioid, figure-of-eight, tripartite and multilobed. Such patterns were largely unrelated to head shadow effects. Blocking the ear canal contralateral to there corded ear was shown to effectively abolish CM directionality, largely by eliminating regions of insensitivity to sound. It is inferred that the quail ear functions as an asym metrical pressure gradient receiver, the pressure gradient function being mediated by the interauralcavity. It is proposed that the central auditory system codes directional information by a null detecting method and computes an unambiguous (i.e.intensity independent) directional cue. This spatial cue is achieved by the difference between the directional sensitivities of the two ears, defined as the Directional Index (DI). The spatial distribution of DI values (difference pattern) demonstrated ranges and peaks which closely reflected the extent and position of nulls determined from monaural directivity functions. Large directional cues (up to 25 dB) extended throughout most of the audible spectrum of the quail and the sharpness of difference patterns increased with frequency. Primary ‘best’ directions, estimated from peaks in difference patterns, tended to move towards the front of the head at higher frequencies; rearward secondary peaks also occurred. From the properties of directional cues it is suggested that the ability of birds to localize sound need not necessarily depend on frequency; however, spatial acuity may be both frequency and direction dependent, and include the possibility of front-torearerrors. The directional properties of bird vocalizations may need to bere assessed on the basis of the proposed mechanism for directional hearing.

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Biophysical Aspects of Directional Hearing in the Tammar Wallaby, Macropus Eugenii

Journal of Experimental Biology ◽

10.1242/jeb.121.1.371 ◽

1986 ◽

Vol 121 (1) ◽

pp. 371-394 ◽

Cited By ~ 1

Author(s):

ROGER B. COLES ◽

ANNA GUPPY

Keyword(s):

Spatial Location ◽

Tammar Wallaby ◽

Directional Hearing ◽

Circular Aperture ◽

External Ear ◽

Acceptance Angle ◽

Macropus Eugenii ◽

Acoustic Axis ◽

Directivity Patterns ◽

Sound Diffraction

The biophysical properties of the external ear of the Tammar wallaby, Macropus eugenii (Desmarest), have been investigated using probe microphones implanted in the ear canal. An acoustic axis of the pinna exists above 2kHz which is located close to the horizonal plane for natural ear positions, whereas azimuthal location of the acoustic axis is determined by pinna orientation on the head. The maximum on-axis acoustic pressure gain of the external ear reaches 25–30 dB for frequencies near 5 kHz. This results from pressure transformation by the horn-like pinna combined with resonance of the auditory meatus. The directionality of the pinna is similar to the sound diffraction properties of a circular aperture with an average radius based on the circumference of the pinna face. These properties determine the acceptance angle of the main lobe containing the acoustic axis and the spatial location of nulls. Large binaural intensity differences, exceeding 30dB, can be produced by the interaction of peaks and nulls between monaural directivity patterns, depending on the relative position of each pinna.

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The Effect of the XM45 Gas Mask and Hood on Directional Hearing

Proceedings of the Human Factors and Ergonomics Society Annual Meeting ◽

10.1177/107118139704100229 ◽

1997 ◽

Vol 41 (2) ◽

pp. 864-867

Author(s):

T. R. Letowski ◽

G. L. Ricard ◽

J. E. Greives

Keyword(s):

Speech Intelligibility ◽

Free Field ◽

Directional Hearing ◽

Directional Sensitivity ◽

Protective Equipment ◽

Spatial Awareness ◽

Hearing Thresholds ◽

Gas Mask ◽

Modified Rhyme Test ◽

Narrow Bands

We measured listeners' directional sensitivity for narrow bands of noise and for speech recognition while they were wearing the XM45 gas mask and hood and compared it to normal free-field listening. Bekesy tracking was used to measure absolute hearing thresholds for 1/3 octave bands of noise centered at 0.125, 0.25, 0.5, 1, 2, 3, 4, 6, and 8 kHz. and masked intelligibility thresholds for speech were measured using the Modified Rhyme Test. Both the noise and speech signals were presented from loudspeakers located at azimuths of 0°, 45°, 90°, 135°, and 180°. The mask and hood significantly elevated noise-band thresholds for those bands centered at 1.0 kHz and above. Sensitivity to masked speech was increased by over 12 dB by lateral loudspeaker placement, and wearing a gas mask and hood reduced this gain by 80 percent. These results document a loss of auditory spatial awareness that has not been apparent from previous studies of speech intelligibility while wearing chemical protective equipment.

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Directional Sensitivity of Microphonic Potentials Form the Perch Ear

Journal of Experimental Biology ◽

10.1242/jeb.60.3.881 ◽

1974 ◽

Vol 60 (3) ◽

pp. 881-899 ◽

Cited By ~ 2

Author(s):

OLAV SAND

Keyword(s):

Sound Source ◽

Horizontal Plane ◽

Anterior Part ◽

Vertical Direction ◽

Directional Sensitivity ◽

Sound Waves ◽

Sound Stimulation ◽

Vibration Direction ◽

Directional Information ◽

The Difference

1. Microphonic potentials were recorded from the lagena and from different parts of the sacculus in the perch during horizontal and vertical vibration of the fish in air. This stimulation technique gives a good simulation of sound stimulation in water. 2. The lagena was predominantly sensitive to vertical vibrations, whereas the anterior part of the sacculus was equally sensitive to vertical and horizontal vibrations. A gradient is seen along the sacculus, in that the more posterior positions show a tendency towards greater relative vertical sensitivity. By comparing the nervous output from the lagena and from the sacculus the fish might thus get information about the vertical direction of the sound source. 3. The amplitude of the saccular microphonic potentials evoked by horizontal vibrations was a function of the vibration direction. Maximal responses were obtained when this direction deviated about 20° from the long axis of the fish, which is approximately parallel to the long axis of the sacculi. The difference in response between the two ears might be utilized to give directional information about the horizontal position of the sound source. 4. Sound-induced pulsations radiating from the swimbladder will be efficient in evoking saccular microphonic potentials. This causes masking of the difference in response between the two ears, but directional information may still be obtained. It is proposed that the power of angle separation in the horizontal plane should be optimal for sound waves side on to the fish, and that a fish possessing a swimbladder may be able to detect the sound direction with higher accuracy in the vertical than in the horizontal plane. 5. The relative effect in evoking microphonic potentials of vertical compared to horizontal vibrations was frequency dependent, and it is concluded that the pattern of otolith movements during sound stimulation may also change with frequency. This phenomenon constitutes a possible basis for peripheral frequency analysis in fish.

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Specification for values for the difference between free-field and pressure sensitivity levels for one-inch standard condenser microphones

10.3403/00121168 ◽

1980 ◽

Keyword(s):

Free Field ◽

Pressure Sensitivity ◽

The Difference

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Predicting Turbulent Boundary Layer Wall Pressure Fluctuations in Adverse Pressure Gradients

Noise Control and Acoustics ◽

10.1115/imece2005-80797 ◽

2005 ◽

Author(s):

Frank J. Aldrich

Keyword(s):

Boundary Layer ◽

Turbulent Boundary Layer ◽

Pressure Gradient ◽

Pressure Fluctuations ◽

Adverse Pressure Gradient ◽

Wall Pressure ◽

Prediction Tool ◽

Pressure Gradients ◽

Wall Pressure Fluctuations ◽

The Difference

A physics-based approach is employed and a new prediction tool is developed to predict the wavevector-frequency spectrum of the turbulent boundary layer wall pressure fluctuations for subsonic airfoils under the influence of adverse pressure gradients. The prediction tool uses an explicit relationship developed by D. M. Chase, which is based on a fit to zero pressure gradient data. The tool takes into account the boundary layer edge velocity distribution and geometry of the airfoil, including the blade chord and thickness. Comparison to experimental adverse pressure gradient data shows a need for an update to the modeling constants of the Chase model. To optimize the correlation between the predicted turbulent boundary layer wall pressure spectrum and the experimental data, an optimization code (iSIGHT) is employed. This optimization module is used to minimize the absolute value of the difference (in dB) between the predicted values and those measured across the analysis frequency range. An optimized set of modeling constants is derived that provides reasonable agreement with the measurements.

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Microvascular pressure in venules of skeletal muscle during arterial pressure reduction

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1986.250.5.h838 ◽

1986 ◽

Vol 250 (5) ◽

pp. H838-H845 ◽

Cited By ~ 10

Author(s):

S. D. House ◽

P. C. Johnson

Keyword(s):

Skeletal Muscle ◽

Blood Flow ◽

Arterial Pressure ◽

Pressure Gradient ◽

Pressure Difference ◽

Reactive Hyperemia ◽

Sartorius Muscle ◽

Pressure Reduction ◽

Large Vein ◽

The Difference

It has been suggested from whole organ studies that the viscosity of blood in skeletal muscle venules varies inversely with flow over physiological flow ranges. If this is the case, the hydrostatic pressure gradient in venules should change less than flow as flow is altered. To test this hypothesis, pressure in venules of cat sartorius muscle was measured during stepwise arterial pressure reduction to 20 mmHg. Large vein pressure remained constant at about 5 mmHg. Average pressures in the large venules (40–185 microns) ranged from 13.6 to 10.0 mmHg. The difference between pressure in these venules and large vein pressure fell in proportion to the reduction in blood pressure and blood flow. Pressures in the smallest venules studied (25 microns) averaged 19.7 +/- 6.2 (SD) mmHg. The pressure difference between the smallest venules and the large vein fell less than the arteriovenous pressure difference or blood flow when arterial pressure was reduced. During reactive hyperemia the pressure gradient between the smallest venules and the large vein rose proportionately less than blood flow. The stability of pressure in the smallest venules is consistent with the hypothesis that blood viscosity varies inversely with flow rate.

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Directional hearing in grasshoppers: neurophysiological testing of a bioacoustic model

Journal of Experimental Biology ◽

10.1242/jeb.202.2.121 ◽

1999 ◽

Vol 202 (2) ◽

pp. 121-133 ◽

Cited By ~ 1

Author(s):

J. Schul ◽

M. Holderied ◽

D.V. Helversen ◽

O.V. Helversen

Keyword(s):

Schistocerca Gregaria ◽

Neuronal Response ◽

Individual Variability ◽

Biophysical Model ◽

Directional Hearing ◽

Complex Stimulus ◽

Directional Information ◽

Model Calculations ◽

Chorthippus Biguttulus ◽

Nerve Recordings

A recently proposed biophysical model for directional hearing in grasshoppers was tested using complex stimulus situations, with two loudspeakers, one on either side of the animal, synchronously emitting sinusoids with defined phase and amplitude relationships. Hearing responses were determined from whole nerve recordings and compared with the predictions of the model. In Schistocerca gregaria, there were only minor differences between the predictions of the model and measurements and, by reducing the value of the gain of the internal sound path measured previously, a close agreement was achieved between model and measured hearing responses. In Chorthippus biguttulus, larger discrepancies between model calculations using the values measured previously and neuronal response functions were found in both shape and amplitude. A better fit between measurements and model predictions was achieved by increasing the values of the internal delay over those measured previously. The measurements presented here indicate high inter-individual variability of the parameters of the internal pathway, with a range of 60 degrees for the internal phase delay. Calculating the directional characteristics using this range of values for the internal delay indicated that sufficient directional information was available down to 5 kHz. Increasing the value of the internal delay over that measured in an earlier study therefore provides an explanation for the discrepancy between the poor directional information attributed to C. biguttulus in that study and the excellent lateralization ability of males of this species at 5 kHz.

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On the Momentum and Thermal Structures of Turbulent Spots in a Favorable Pressure Gradient

Journal of Turbomachinery ◽

10.1115/1.2218520 ◽

2005 ◽

Vol 128 (4) ◽

pp. 689-698 ◽

Cited By ~ 9

Author(s):

T. P. Chong ◽

S. Zhong

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Pressure Gradient ◽

Velocity Component ◽

Thermal Boundary Layer ◽

Temperature Fluctuations ◽

Turbulent Spots ◽

Zone Length ◽

Favorable Pressure Gradient ◽

The Difference

This paper represents the results from an experimental investigation of the flow physics behind the difference in the transition zone length indicated by the momentum boundary layer and thermal boundary layer parameters observed on the suction surfaces of gas turbine blades. The experiments were carried out on turbulent spots created artificially in an otherwise laminar boundary layer developing over a heated flat plate in a zero pressure gradient and a favorable pressure gradient. A specially designed miniature triple wire probe was used to measure the streamwise velocity component U, transverse velocity component V and temperature T simultaneously during the passage of the spots. In this paper, the general characteristics of the ensemble-averaged velocity and temperature perturbations, rms fluctuations, and the second moment turbulent quantities are discussed and the influence of favorable pressure gradient on these parameters is examined. When a favorable pressure gradient is present, unlike in the velocity boundary layer where significant velocity fluctuations and Reynolds shear stress occur both on the plane of symmetry and the spanwise periphery, high temperature fluctuations (and turbulent heat fluxes) are confined in the plane of symmetry. The difference in the levels of velocity/temperature fluctuations at these two locations gives an indication of the effectiveness of momentum/heat transfer across the span of the spots. The results of this study indicate that the heat transfer within a spot is inhibited more than that of the momentum transfer at the presence of a favorable pressure gradient. This phenomenon is expected to slow down the development of a transitional thermal boundary layer, leading to a longer transitional zone length indicated by the heat transfer parameters as reported in the literature.

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