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At least 1,243 records · Page 69Linked to original sources
PubMed1997

A backpropagation network model of the monaural localization information available in the bat echolocation system.

The information echolocating bats receive is a combination of the properties of the sound they emit and the sound they receive at the eardrum. Convolving the emission and the external ear transfer functions produces the full spectral information contained in the echolocation combination. Spatially dependent changes in the magnitude spectra of the emission, external ear transfer functions, and the echolocation combination of Eptesicus fuscus could provide localization information to the bat. Principal component analysis was used to reduce the dimensionality of these complex spectral data sets. The first eight principal component weights were normalized, rotated, and used as the input to a backpropagation network model which examined the relative directionality of the emission, ear, and the echolocation combination. The model was able to localize more accurately when provided with the directional information of the echolocation combination compared to either the emission or ear information alone.

Animals↗
PubMed1998

One tone, two ears, three dimensions: a robotic investigation of pinnae movements used by rhinolophid and hipposiderid bats.

Bats, which echolocate using broadband calls, are believed to employ the passive acoustic filtering properties of the head and pinnae to provide spectral cues which encode 3-D target angle. Microchiropteran species whose calls consist of a single, constant frequency harmonic (i.e., some species in the families Rhinolophidae and Hipposideridae) may create additional acoustic localization cues via vigorous pinna movements. In this work, two types of echolocation cues generated by moving a pair of receivers aboard a model sensor head are investigated. In the first case, it is supposed that a common 3-D echolocation principle employed by all bats is the creation of alternative viewing perspectives, and that constant frequency (CF) echolocators use pinna movement rather than morphology to alter the acoustic axes of their perceptual systems. Alternatively, it is possible rhinolophids and hipposiderids move their ears to create dynamic cues--in the form of frequency and amplitude modulations--which vary systematically with target elevation. Here the use of binaural and monaural timing cues derived from amplitude modulated echo envelopes are investigated. In this case, pinna mobility provides an echolocator with a mechanism for creating dramatic temporal cues for directional sensing which, unlike interaural timing differences, do not degrade with head size.

Animals↗
PubMed1999

Acoustic flow perception in cf-bats: properties of the available cues.

Signal design in cf-bats is hypothesized to be commensurate with the evaluation of time-variant echo parameters, imposed by changes in the sound channel occurring as the bat flies by a target. Two such parameters, the proportional changes in Doppler frequency and sound pressure amplitude, are surveyed, employing a simplified acoustic model in order to assess their fitness for target localization given a translational movement within a plane. This is accomplished by considering the properties of the scalar fields given by the value of these putative sensory variables as a function of position in a plane. The considered criteria are: existence and extent of ambiguity areas (i.e., multiple solutions for target position), magnitude of the variables (relevant with regard to perceptual thresholds), as well as magnitude and orthogonality of the gradients (relevant to localization accuracy). It is concluded that these properties render the considered variables compatible with gross judgements of target position. This may be sufficient for behavioral contexts like obstacle avoidance, where adoption of suitable safety margins could compensate for the variance and bias associated with estimates of target location.

Animals↗
PubMed1976

Coordinated activities of middle-ear and laryngeal muscles in echolocating bats.

The middle-ear muscles and laryngeal muscles of the little brown bat (Myotis lucifugus) are highly developed. When the bat emits orientation sounds, action potentials of middle-ear muscles appear approximately 3 milliseconds after those of the laryngeal muscles; this activity of middle-ear muscles attenuates the vocal self-stimulation and improves the performance of the echolocation system. When an acoustic stimulus is delivered, both types of muscles contract; action potentials of the laryngeal muscles appear approximately 3 milliseconds after those of the middle-ear muscles. These two groups of muscles are apparently activated in a coordinated manner not only by the nerve impulses from the vocalization center, but also by those from the auditory system.

Action Potentials↗
PubMed1965

MOTH SOUNDS AND THE INSECT-CATCHING BEHAVIOR OF BATS.

Captive bats trained to catch mealworms tossed in midair turned away from most of these targets when simultaneously confronted with a recorded train of the ultrasonic pulses generated by an Arctiid moth. When similarly exposed to the recorded echolocation pulses of another bat, presented at the same intensity as the "moth" sounds, they were not so affected.

Animals↗
PubMed1970

Echo-ranging neurons in the inferior colliculus of bats.

Bats measure the distance to an object in terms of the time lag between their outgoing orientation sounds and the returning echo. For measurement of the time lag, the latency of response of a neuron to a stimulus must be nearly constant regardless of the stimulus amplitude and envelope. Otherwise, a large error would be introduced into the measurement. Bats have neurons that are specialized for echo ranging.

Animals↗
PubMed1971

Echolocation in bats: signal processing of echoes for target range.

Echolocating bats Eptesicus fuscus and Phyllostomus hastatus can discriminate between the nearer and farther of two targets. Their errors in discrimination are predicted accurately by the autocorrelation functions of their sonar cries. These bats behave as though they have an ideal sonar system which cross correlates the transmitted cry with the returning echo to extract targetrange information.

Animals↗
PubMed1972

Rabies virus in nasal mucosa of naturally infected bats.

Rabies virus was demonstrated in the olfactory mucosa of naturally infected bats by staining with fluorescent antibody and by isolation of the virus from the nasal tissues. The olfactory mucosa is a potential portal of entry and exit for airborne rabies virus in bat caves.

Animals↗
PubMed1972

Vampire bat control by systemic treatment of livestock with an anticoagulant.

The blood of beef cattle given single doses (1 milligram per kilogram of body weight) of diphenadione (2-diphenylacetyl-1,3-indandione) became toxic to vampire bats (Desmodus rotundus) and remained toxic for 3 days without harming the cattle. Cattle at three ranches in Mexico treated with single intraruminal injections of diphenadione experienced a reduction in vampire bat bites of 93 percent. Bioassays of milk and liver from cattle treated orally with diphenadione in the laboratory indicated that there were no residue problems.

Administration, Oral↗
PubMed1974

Site of neural attenuation of responses to self-vocalized sounds in echolocating bats.

Bats of the genus Myotis emit intense orientation sounds for echolocation. If such sounds directly stimulated their ears, the detection of echoes from short distances would be impaired. In addition to the muscular mechanism in the middle ear, the bat has a neural mechanism in the brain for attenuation of responses to self-vocalized orientation and nonorientation sounds. This neural attenuating mechanism operates in the nucleus of the lateral lemniscus, reducing its activity by about 15 decibels, and it is synchronized with vocalization.

Acoustic Stimulation↗
PubMed1974

Target structure and echo spectral discrimination by echolocating bats.

Echolocating bats can use sonar to discriminate among targets which reflect echoes differing in spectral distribution of energy but not in overall intensity. They can detect differences smaller than 1 millimeter in fine target structure. Bats may be capable of classifying targets from echo spectral signatures and might thus be able to distinguish among flying insect prey by sonar.

Animals↗
PubMed1977

Amplitude spectrum representation in the Doppler-shifted-CF processing area of the auditory cortex of the mustache bat.

The mustache bat, Pteronotus parnellii rubiginosus, emits orientation sounds containing a long constant-frequency (CF) component that is ideal for echo detection and Doppler shift measurement. About 30 percent of the primary auditory cortex of this bat is chiefly devoted to processing the second harmonic of the CF component in Doppler-shifted echoes. In this Doppler-shifted-CF processing area, single neurons recorded in any electrode penetration perpendicular to the cortical surface have nearly identical best frequencies and best amplitudes (or best pressure levels) at which the neurons show maximum excitation. The best frequency and best amplitude vary systematically with the location of the neurons in the cerebral cortex, so that there are tonotopic and "amplitopic" representation axes, which are radial and eccentric, respectively. In other words, the best-frequency and best-amplitude contours are eccentric and radial, respectively. The amplitude spectrum of a signal is thus represented in the coordinates of amplitude and frequency parallel to the cortical surface. This amplitude spectrum representation is disproportionate according to perceptual significance, so that a signal of 61.5 to 62.0 kilohertz and 30 to 50 decibels SPL (sound pressure level) is projected to a larger area than other signals. Just outside this Doppler-shifted-CF processing area, neurons are found which are specialized for responding to a particular information-bearing element or a particular combination of information-bearing elements in orientation sounds and echoes consisting of CF and frequency-modulated components.

Animals↗
PubMed1987

Auditory pathways to the frontal cortex of the mustache bat, Pteronotus parnellii.

In primates, certain areas of the frontal cortex play a role in guiding movements toward visual or auditory objects in space. The projections from auditory centers to the frontal cortex of the bat Pteronotus parnellii were examined because echolocating bats utilize auditory cues to guide their movements in space. An area in the frontal cortex receives a direct projection from a division of the auditory thalamus, the suprageniculate nucleus, which in turn receives input from the anterolateral peri-olivary nucleus, an auditory center in the medulla. This pathway to the frontal cortex bypasses the main auditory centers in the midbrain and cortex and could involve as few as four neurons between the cochlea and the frontal cortex. The auditory cortex is also a major source of input to the frontal cortex. This area of the frontal cortex may link the auditory and motor systems by its projections to the superior colliculus.

Animals↗
PubMed1996

Corticofugal modulation of time-domain processing of biosonar information in bats.

The Jamaican mustached bat has delay-tuned neurons in the inferior colliculus, medial geniculate body, and auditory cortex. The responses of these neurons to an echo are facilitated by a biosonar pulse emitted by the bat when the echo returns with a particular delay from a target located at a particular distance. Electrical stimulation of cortical delay-tuned neurons increases the delay-tuned responses of collicular neurons tuned to the same echo delay as the cortical neurons and decreases those of collicular neurons tuned to different echo delays. Cortical neurons improve information processing in the inferior colliculus by way of the corticocollicular projection.

Acoustic Stimulation↗
PubMed1978

Aural representation in the Doppler-shifted-CF processing area of the auditory cortex of the mustache bat.

In the mustache bat (Pteronotus pamellii rubiginosus) the frequency and amplitude of an acoustic signal are represented in the coordinates parallel to the surface of the Doppler-shifted-CF (constant frequency) processing area ofthe primary auditory cortex. In this area all cortical neurons studied were excited by contralateral stimuli, and almost all of them were either excited or inhibited by ipsilateral stimuli. These are called E-E (ipsilateral and contralateral excitatory) and I-E (ipsilateral inhibitory and contralateral excitatory) neurons, respectively. The I-E neurons are directionally sensitive, while the E-E neurons are not. The E-E neurons are equally sensitive to echoes between 30 degrees contralateral and 30 degrees ipsilateral. Of the electrode penetrations orthogonal to the Doppler-shifted-CF processing area, 57 percent were characterized by either E-E or I-E neurons. Thus, there are at least two types of binaural columns: E-E columns, mainly located in a ventral part of the Doppler-shifted-CF processing area, where neurons are tuned to weak echoes; and IE columns, mainly distributed in a dorsal part, where neurons are tuned to moderate to intense echoes. Therefore, neurons tuned to weaker echoes integrate or even multiply faint signals from both ears for effective detection of a distant small target, while neurons tuned to moderate to intense echoes are suited for processing directional information and are stimulated when a bat approaches a target at short range. The Doppler-shifted-CF processing area may be considered to consist of two functional subdivisions.

Animals↗
PubMed1979

Echolocation and pursuit of prey by bats.

Echolocating bats use different information-gathering strategies for hunting prey in open, uncluttered environments, in relatively open environments with some obstacles, and in densely cluttered environments. These situations differ in the extent to which individual targets such as flying insects can be detected as isolated objects or must be separated perceptually from backgrounds. Echolocating bats also differ in whether they use high-resolution, multidimensional images of targets or concentrate specifically on one particular target dimension, such as movement, to detect prey.

Animals↗
PubMed1976

Bat mortality: pesticide poisoning and migratory stress.

Organochlorine residues in the fat of young Mexican free-tailed bats, Tadarida brasiliensis, reached the brain and caused symptoms of poisoning after the fat mobilization that takes place during migratory flight was simulated. These chemical body burdens were obtained naturally under free-living conditions at the maternity roost. The data obtained support the hypothesis that pesticides have contributed to recent declines in populations of this bat.

Adipose Tissue↗