The role of the flight membranes in insect capture by bats

Webster, Frederic A.; Griffin, Donald R.

doi:10.1016/0003-3472(62)90056-8

Cited by 84 publications

(29 citation statements)

References 7 publications

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“…Since the bat could not make a decision by a direct comparison of both targets it is very likely that bats measured absolute distances (Simmons and Lavender 1976). The ranging thresholds obtained in two alternative forced choice experiments are also close to the accuracy estimated for flying, insect hunting bats (Webster and Griffin 1962;Trappe and Schnitzler 1982).…”

Section: Ranging Performance At -28 Db Relative Echo Splmentioning

confidence: 66%

Echo SPL influences the ranging performance of the big brown bat, Eptesicus fuscus

Denzinger

Schnitzler

1994

J Comp Physiol A

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Four bats of the species Eptesicus fuscus were trained in a two-alternative forced-choice procedure to discriminate between two phantom targets that differed in range. The rewarded stimulus was located at a distance of 52.7 cm, while the other unrewarded stimulus was further away. Only one target was presented at a time. In the first experiment we measured the range discrimination performance at an echo SPL of -28 dB relative to the bat's sonar transmission. A 75% correct performance level was arbitrarily defined as threshold and was obtained at a delay difference of 80 microseconds, corresponding to a range difference of 13.8 mm. In the second experiment the delay difference was fixed at 150 microseconds and the echo SPL varied between -8 and -48 dB relative to sonar emissions. The performance of the bats depended on the relative echo SPL. AT -28 dB the bats showed the best performance. It deteriorated at an increase of the relative echo SPL to -18 dB and -8 dB. The performance also deteriorated when the relative echo SPL was reduced to -38 dB and -48 dB. Only at low relative echo SPLs did the bats partially compensate for the reduction in echo SPL and increased the SPL of their emitted signals by a few dB. Our results support the hypothesis that neurons exhibiting paradoxical latency shift may be involved in encoding target range. This hypothesis predicts a decrease in performance at high echo SPLs as we found it in our experiments. The observed reduction in performance at very low echo SPLs may be due to a decrease in S/N ratio.

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Section: Ranging Performance At -28 Db Relative Echo Splmentioning

confidence: 66%

Echo SPL influences the ranging performance of the big brown bat, Eptesicus fuscus

Denzinger

Schnitzler

1994

J Comp Physiol A

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“…This does not reduce the bats' ranging accuracy since the threshold is the same as in the other ranging experiments with two targets. The threshold is also close to the accuracy of 1-3 cm estimated for bats catching insects in free air (Webster and Griffin 1962). Hence, it is likely that the bats treat ranging experiments with simulated targets as a ranging task even in triggered play back experiments.…”

Section: Discussionmentioning

confidence: 81%

Target ranging and the role of time-frequency structure of synthetic echoes in big brown bats, Eptesicus fuscus

Surlykke

1992

J Comp Physiol A

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Echolocating bats judge the distance to a target on basis of the delay between the emitted cry and the returning echo. In a phantom echo set-up it was investigated how changes in the time-frequency structure of synthetic echoes affect ranging accuracy of big brown bats, Eptesicus fuscus.A one channel phantom target simulator and a Y/N paradigm was used. Five Eptesicusfuscus were trained to discriminate between phantom targets with different virtual distances (delays). The phantom echo was stored in a memory and broadcast from a loudspeaker after a certain delay following the bat's triggering of the system via a trigger microphone. The ranging accuracy was compared using 5 different signals with equal energy as phantom echoes: a standard cry (a natural bat cry), two kinds of noise signals, a high pass, and a low pass filtered version of the standard cry.The standard cry was recorded from one of the bats while judging the distance to a real target. The duration was 1.1 ms, the first harmonic swept down from 55 to 25 kHz and there was energy also in the second and third harmonic. Both noise signals had the same duration, power spectrum, and energy as the standard cry. One noise signal was stored in a memory and hence was exactly the same each time the bat triggered the system. The other variable noise signal was produced by storing the envelope of the standard cry and multiplying on-line with band pass filtered noise. The time-frequency structure (e.g. rise time) of this noise signal changed from triggering to triggering. The filtered signals were produced by either 40 kHz high pass or 40 kHz low pass filtering of the standard cry.The range difference thresholds for the 5 bats were around 1-2 cm (51-119 gs) using the standard cry as echo. The range difference threshold with both noise Abbreviations: FM frequency modulated; CF constant frequency; peSPL peak equivalent sound pressure level; SD standard deviation; SE standard error of mean; EPROM erasable programmable read only memory; FFT fast Fourier transform; SIN signal-to-noise ratio signals was 7-8 cm (around 450 gs delay difference). The 40 kHz high pass filtered cry increased the threshold to approximately twice the threshold with the standard cry. With the 40 kHz low pass filtered cry the threshold was increased 2.5-3 times relative to the threshold with the standard cry. A single bat was tested with a signal filtered with a 55 kHz low pass filter leaving the whole first harmonic. The threshold was the same as that with the standard signal.The reduced ranging accuracy with the filtered signals indicates that the full band width of the first harmonic is utilised for ranging by the bats. The substantial reduction in accuracy with the noise signals indicates that not only the full band width but also the orderly timefrequency structure (the FM sweep) of the cry is important for ranging in echolocating bats.

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“…If the bat's only use for the range axis in perception is to coordinate reaching out with its wing or tail to seize an airborne target, there would be no need for a target-ranging accuracy of a fraction of a millimeter (Simmons 1987(Simmons , 1989. To perceive the small range separations between glints in biologically realistic targets , the bat would have to register the absolute range of the target with considerable accuracy -certainly greater accuracy than the 1 to 2 cm needed to intercept insect prey (Trappe 1982;Webster and Griffin 1962). That is, if the bat converts spectrally-represented target shape into a true range-axis estimate of the separation of glints in the target, the range axis would need to have an intrinsic accuracy great enough to accept this transformed spectral information.…”

Section: Discussionmentioning

confidence: 99%

Convergence of temporal and spectral information into acoustic images of complex sonar targets perceived by the echolocating bat, Eptesicus fuscus

1990

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FM echolocating bats (Eptesicus fuscus)were trained to discriminate between a two-component complex target and a one-component simple target simulated by electronically-returned echoes in a series of experiments that explore the composition of the image of the two-component target. In Experiment I, echoes for each target were presented sequentially, and the bats had to compare a stored image of one target with that of the other. The bats made errors when the range of the simple target corresponded to the range of either glint in the complex target, indicating that some trace of the parts of one image interfered with perception of the other image. In Experiment II, echoes were presented simultaneously as well as sequentially, permitting direct masking of echoes from one target to the other. Changes in echo amplitude produced shifts in apparent range whose pattern depended upon the mode of echo presentation.2. Eptesicus perceives images of complex sonar targets that explicitly represent the location and spacing of discrete glints located at different ranges. The bat perceives the target's structure in terms of its range profile along a psychological range axis using a combination of echo delay and echo spectral representations that together resemble a spectrogram of the FM echoes. The image itself is expressed entirely along a range scale that is defined with reference to echo delay. Spectral information contributes to the image by providing estimates of the range separation of glints, but it is transformed into these estimates.3. Perceived absolute range is encoded by the timing of neural discharges and is vulnerable to shifts caused by neural amplitude-latency trading, which was estimated at 13 to 18 gs per dB from N1 and N4 auditory evoked potentials in Eptesicus. Spectral cues representing the separation of glints within the target are transformed into estimates of delay separations before being incorporated into the image. However, because they are encoded * Present address: by neural fi'equency tuning rather than the time-of-occurrence of neural discharges, the perceived range separation of glints in images is not vulnerable to amplitudelatency shifts.4. The bat perceives an image that is displayed in the domain of time or range. The image receives no evident spectral contribution beyond what is transformed into delay estimates. Although the initial auditory representation of FM echoes is spectrogram-like, the time, frequency, and amplitude dimensions of the spectrogram appear to be compressed into an image that has only time and amplitude dimensions. The spectral information is not lost but manifests itself as equivalent time-domain information.

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The role of the flight membranes in insect capture by bats

Cited by 84 publications

References 7 publications

Echo SPL influences the ranging performance of the big brown bat, Eptesicus fuscus

Echo SPL influences the ranging performance of the big brown bat, Eptesicus fuscus

Target ranging and the role of time-frequency structure of synthetic echoes in big brown bats, Eptesicus fuscus

Convergence of temporal and spectral information into acoustic images of complex sonar targets perceived by the echolocating bat, Eptesicus fuscus

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