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D J Hartley

Publications and source records attributed to D J Hartley.

6 recordsLinked to original sources
PubMed1992

Spatial processing within the mustache bat echolocation system: possible mechanisms for optimization.

1. The directionality of an echolocation system is determined by the acoustic properties of both the emitter and receiver, i.e., by the radiation pattern of the emitted pulse and the directionally of the external ears. We measured the directionality of the echolocation system of the greater mustache bat (Pteronotus parnellii) at the 30 kHz, 60 kHz and 90 kHz harmonics of its echolocation pulse by summing, at points throughout the frontal sound field, the echo attenuation due to the spread of pulse energy and the attenuation due to the spread of pulse energy and the attenuation due to the directionality of its external ears. The pulse radiation pattern at the 3 harmonics was measured by comparing the output of a microphone moved throughout the frontal sound field against a second reference microphone at the center of the field. External ear directionality at the 3. harmonics was measured by presenting free-field sounds throughout the frontal sound field, and recording the intensity thresholds of cochlear microphonic potentials, and the intensity thresholds of monaural neurons in the inferior colliculus tuned to one of the 3 harmonics. 2. When compared with ear directionality, the echolocation system was found to be more directional for the center of the sound field in several respects. At all harmonics, attenuation of sounds originating in the peripheral part of the field was increased by 10 to 13 dB. Areas of maximum sound intensity contracted toward the center of the field. Also, the isointensity contours of the echolocation system were more radially symmetrical about the center of the field. 3. At 60 kHz, sound intensity along the azimuth within the echolocation system was nearly constant 26 degrees to either side of the center of the field. This suggests that the radiation pattern of the echolocation pulse and the directionality of the external ears complement one another to produce an acoustic environment at the center of the sound field in which stimulus intensity is stabilized to allow more effective analysis of various aspects of the echolocation target. In particular, we suggest that this intensity stabilization may allow the bat to more effectively resolve the interaural intensity differences it uses to localize prey. 4. Predictions of the azimuthal spatial tuning of binaurally sensitive neurons in the inferior colliculus within the echolocation system were compared with their spatial tuning when only ear directionality is considered.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1992

Stabilization of perceived echo amplitudes in echolocating bats. I. Echo detection and automatic gain control in the big brown bat, Eptesicus fuscus, and the fishing bat, Noctilio leporinus.

Previous research on echo detection in bats has suggested that the effective threshold is a function of the acoustic clutter in the experimental environment, as might be expected given the low ambient noise levels typical of such psychophysical research. This paper demonstrates that theory of signal detectability (TSD) methodology is applicable to bats and uses it to show that an important element of clutter limiting in Eptesicus fuscus and Noctilio leporinus is backward masking of phantom targets by the real echo from the loudspeakers used to generate them. This information suggests that a previous estimate of the magnitude of automatic gain control (AGC) is too high, due to variable backward masking inherent in the experimental method used. A re-examination of gain control using a masking-free method shows that it reduces auditory sensitivity by 6 to 7 dB per halving of target range, rather than 11 dB as previously thought.

Animals↗
PubMed1992

Stabilization of perceived echo amplitudes in echolocating bats. II. The acoustic behavior of the big brown bat, Eptesicus fuscus, when tracking moving prey.

Big brown bats, Eptesicus fuscus, can be trained to use echolocation to track a small microphone with a food reward attached when it is moved rapidly toward them. This situation mimics prey interception in the wild while allowing very precise recording of the sonar pulses emitted during tracking behavior. The results show that E. fuscus intensity compensates, reducing emitted intensity by 6 dB per halving of target range so that the intensity incident upon the target is constant and echo intensity increases by 6 dB per halving of range. This increase in echo intensity is effectively canceled by the reduction in auditory sensitivity due to automatic gain control (AGC) of 6 to 7 dB per halving of range. Intensity compensation behavior and AGC therefore form a dual-component, symmetrical system that stabilizes perceived echo amplitudes during target approach. The same system is present in the fishing bat, Noctilio leporinus, suggesting that it may be widespread in echolocating bats. Correlation analysis shows that, despite large changes in the duration of the pulses emitted by E. fuscus during an approach, the pulse frequency structure is such that the spatial image of the target perceived along the range axis is highly stable. Pulse duration is not reduced in the manner theoretically necessary to eliminate potential echo distortion effects due to AGC, but is reduced in such a way that this distortion is insignificant. During the terminal buzz, a high degree of temporal overlap (relative to pulse duration) occurs between emitted pulse and returning echo.

Animals↗
PubMed1988

The acoustic role of tracheal chambers and nasal cavities in the production of sonar pulses by the horseshoe bat, Rhinolophus hildebrandti.

The acoustic role of the enlarged, bony, nasal cavities and rigid tracheal chambers in the horseshoe bat, Rhinolophus hildebrandti (Fig. 2) was investigated by determining the effect of their selective filling on the nasally emitted sonar pulse and on the sound traveling backwards down the trachea. Normal sonar signals of this bat contain a long constant frequency component with most energy in the second harmonic at about 48 kHz. The fundamental is typically suppressed 20 to 30 dB below the level of the second harmonic (Fig. 1). None of the experimental manipulations described affected the frequency of the sonar signal fundamental. Filling the dorsal and both lateral tracheal chambers had little effect on the emitted vocalization, but caused the level of the fundamental component in the trachea to increase 15 to 19 dB in most bats (Table 2). When only the dorsal chamber or only the two lateral chambers were filled, the effect was less striking and more variable (Tables 3 and 4), suggesting that the tracheal fundamental is normally suppressed by acoustic interaction between these three cavities. Filling the enlarged dorsal nasal cavities had no effect on the tracheal sound. The effect of this treatment on the nasally emitted sonar pulse was inconsistent. Sometimes the fundamental increased 10 to 12 dB, other times the intensity of all harmonics decreased; in still other cases the second, third or fourth harmonic increased, but the fundamental remained unchanged (Tables 5, 6, and 7). When bats were forced to vocalize through the mouth, by sealing the nostrils, there was a prominent increase in the level of the emitted fundamental (10 to 21 dB) and in the fourth harmonic (6 to 17 dB). In one instance there was also a significant increase in the level of the third harmonic (Tables 8 and 9). The supraglottal tract thus filters the fundamental from the nasally emitted sonar signal, although the role of the inflated nasal cavities in this process is unclear. We conclude that a high glottal impedance acoustically isolates the subglottal from the supraglottal vocal tract. The tracheal chambers do not affect the emitted sonar signal, but may attenuate the fundamental in the trachea and prevent it from being reflected from the lungs back towards the cochlea. It may be important to prevent the reflected fundamental from stimulating the cochlea, via tissue conduction, along multiple indirect pathways which would temporally smear cochlear stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

The sound emission pattern and the acoustical role of the noseleaf in the echolocating bat, Carollia perspicillata.

Carollia perspicillata (Phyllostomidae) is a frugivorous bat that emits low-intensity, broadband, frequency-modulated echolocation pulses through nostrils surrounded by a noseleaf. The emission pattern of this bat is of interest because the ratio between the nostril spacing and the emitted wavelength varies during the pulse, causing complex interference patterns in the horizontal dimension. Sound pressures around the bat were measured using a movable microphone and were referenced to those at a stationary microphone positioned directly in front of the animal. Interference between the nostrils was confirmed by blocking one nostril, which eliminated sidelobes and minima in the emission pattern, and by comparison of real emission patterns with simple computer models. The positions of minima in the patterns indicate effective nostril spacings of over a half-wavelength. Displacement of the dorsal lancet of the noseleaf demonstrated that this structure directs sound in the vertical dimension.

Acoustics↗