Silvio Macías

Silvio Macías
Texas A&M University | TAMU

PhD

About

43
Publications
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551
Citations
Introduction
Additional affiliations
February 2014 - March 2016
Goethe-Universität Frankfurt am Main
Position
  • PostDoc Position

Publications

Publications (43)
Presentation
Spectrotemporal modulations are a prominent feature of natural sounds including animal vocalizations and human speech. Echolocating bats must process spectrotemporal cues such as echo delays and spectrum properties to navigate their environment; however, the neuronal networks in the primary auditory cortex (A1) that process features of natural soun...
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There is consensus that primary auditory cortex (A1) utilizes a combination of rate codes and temporally precise population codes to represent discreet auditory objects. During the response to auditory streams, forward suppression constrains cortical rate coding strategies, but it may also be well positioned to enhance temporal coding strategies th...
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Echolocating bats rely upon spectral interference patterns in echoes to reconstruct fine details of a reflecting object's shape. However, the acoustic modulations required to do this are extremely brief, raising questions about how their auditory cortex encodes and processes such rapid and fine spectrotemporal details. Here, we tested the hypothesi...
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The Mexican free-tailed bat, Tadarida brasiliensis, is a fast-flying bat that hunts by biosonar at high altitudes in open space. The auditory periphery and ascending auditory pathways have been described in great detail for this species, but nothing is yet known about its auditory cortex. Here we describe the topographical organization of response...
Article
Little is known about the neural mechanisms that mediate differential action-selection responses to communication and echolocation calls in bats. For example, in the big brown bat, FM food-claiming communication calls closely resemble FM echolocation calls, which guide social and orienting behaviors, respectively. Using advanced signal processing m...
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We studied the columnar and layer-specific response properties of neurons in the primary auditory cortex (A1) of six (four females, two males) anesthetized free-tailed bats, Tadarida brasiliensis, in response to pure tones and down and upward frequency modulated (FM; 50 kHz bandwidth) sweeps. In addition, we calculated current source density (CSD)...
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In many mammals, upward-sweeping frequency-modulated (FM) sounds (up-chirps) evoke larger auditory brainstem responses than downward-sweeping sounds (down-chirps). To determine if similar effects occur in FM echolocating bats, auditory evoked responses (AERs) in big brown bats in response to up-chirps and down-chirps at different chirp durations an...
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Temporal analysis of sound is fundamental to auditory processing throughout the animal kingdom. Echolocating bats are powerful models for investigating the underlying mechanisms of auditory temporal processing, as they show microsecond precision in discriminating the timing of acoustic events. However, the neural basis for microsecond auditory disc...
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To navigate in the natural environment, animals must adapt their locomotion in response to environmental stimuli. The echolocating bat relies on auditory processing of echo returns to represent its surroundings. Recent studies have shown that echo flow patterns influence bat navigation, but the acoustic basis for flight path selection remains unkno...
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Echolocating bats must process temporal streams of sonar sounds to represent objects along the range axis. Neuronal echo-delay tuning, the putative mechanism of sonar ranging, has been characterized in the inferior colliculus (IC) of the mustached bat, an insectivorous species that produces echolocation calls consisting of constant frequency (CF) a...
Article
We investigated response selectivity of single neurons in the inferior colliculus (IC) of the big brown bat, Eptesicus fuscus, to acoustic elements embedded in the natural temporal patterning of dynamic frequency modulated (FM) echolocation sequences. Acoustic stimuli consisted of species-specific sonar sequences, with natural dynamic spectro-tempo...
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The mechanisms by which the mammalian brain copes with information from natural vocalization streams remain poorly understood. This article shows that in highly vocal animals, such as the bat species Carollia perspicillata, the spike activity of auditory cortex neurons does not track the temporal information flow enclosed in fast time-varying vocal...
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It has been reported previously that in the inferior colliculus of the bat Molossus molossus, neuronal duration tuning is ambiguous because the tuning type of the neurons dramatically changes with the sound level. In the present study, duration tuning was examined in the auditory cortex of M. molossus to describe if it is as ambiguous as the collic...
Article
While approaching an object, echolocating bats decrease the amplitude of their vocalizations. This behavior is known as “echo-level compensation.” Here, the activation pattern of the cortical FM-FM (frequency modulated) area of the mustached bat is assessed by using acoustic stimuli that correspond to sonar signals and their echoes emitted during e...
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In the cochlea of the mustached bat, cochlear resonance produces extremely sharp frequency tuning to the dominant frequency of the echolocation calls, around 61 kHz. Such high frequency resolution in the cochlea is accomplished at the expense of losing temporal resolution because of cochlear ringing, an effect that is observable not only in the coc...
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Distress vocalizations (also known as alarm or screams) are an important component of the vocal repertoire of a number of animal species, including bats, humans, monkeys and birds, among others. Although the behavioral relevance of distress vocalizations is undeniable, at present, little is known about the rules that govern vocalization production...
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During echolocation, bats estimate distance to avoid obstacles and capture moving prey. The primary distance cue is the delay between the bat's emitted echolocation pulse and the return of an echo. In the bat's auditory system, echo delay-tuned neurons that only respond to pulse-echo pairs having a specific echo delay serve target distance calculat...
Article
. In this study, we evaluate the potential of the heterodyne system for the acoustic identification of bat species from Mormoopidae in Cuba. The heterodyne transformation of the echolocation calls of the three mormoopid species of Pteronotus (P. macleayii, P. quadridens and P. parnellii) was initially analyzed by setting the frequency of the hetero...
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Full-text available
It has been reported previously that in the inferior colliculus of the bat Molossus molossus, neuronal duration tuning is ambiguous because the tuning type of the neurons dramatically changes with the sound level. In the present study, duration tuning was examined in the auditory cortex of M. molossus to describe if it is as ambiguous as the collic...
Article
Computational brain maps as opposed to maps of receptor surfaces strongly reflect functional neuronal design principles. In echolocating bats, computational maps are established that topographically represent the distance of objects. These target range maps are derived from the temporal delay between emitted call and returning echo and constitute a...
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In the auditory system, tuning to sound level appears in the form of non-monotonic response-level functions that depict the response of a neuron to changing sound levels. Neurons with non-monotonic response-level functions respond best to a particular sound pressure level (defined as "best level" or level evoking the maximum response). We performed...
Article
Echolocating bats use the time from biosonar pulse emission to the arrival of echo (defined as echo delay) to calculate the space depth of targets. In the dorsal auditory cortex of several species, neurons that encode increasing echo delays are organized rostrocaudally in a topographic arrangement defined as chronotopy. Precise chronotopy could be...
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Echolocating bats use the time elapsed from biosonar pulse emission to the arrival of echo (defined as echo-delay) to assess target-distance. Target-distance is represented in the brain by delay-tuned neurons that are classified as either "heteroharmonic" or "homoharmormic." Heteroharmonic neurons respond more strongly to pulse-echo pairs in which...
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Echolocation in bats requires a precise temporal processing of complex signals. This processing of time includes the encoding of echo-delay, which gives an estimation of target distance, and sound duration, which is considered to be important for own sound or echo recognition. In this study, we report that delay-tuned neurons in the inferior collic...
Article
Delay tuning was studied in the auditory cortex of Pteronotus quadridens. All the 136 delay-tuned units that were studied responded strongly to heteroharmonic pulse-echo pairs presented at specific delays. In the heteroharmonic pairs, the first sonar call harmonic marks the timing of pulse emission while one of the higher harmonics (second or third...
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Neuronal computation of object distance from echo delay is an essential task that echolocating bats must master for spatial orientation and the capture of prey. In the dorsal auditory cortex of bats, neurons specifically respond to combinations of short frequency-modulated components of emitted call and delayed echo. These delay-tuned neurons are t...
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One role of the inferior colliculus (IC) in bats is to create neuronal delay-tuning, which is used for the estimation of target distance in the echolocating bat's auditory system. In this study, we describe response properties of IC delay-tuned neurons of the mustached bat (Pteronotus parnellii) and compare it with those of delay-tuned neurons of t...
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Echolocation signals were recorded from the Macleay’s bat (Pteronotus macleayii) while hunting for insects in the field. Search, approach and terminal phases were identified in the foraging activity of the species. During search phase, P. macleayii emitted calls consisting of a short CF component followed by a downward FM sweep (sCF-FM), typical of...
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We studied duration tuning in neurons of the inferior colliculus (IC) of the mustached bat. Duration-tuned neurons in the IC of the mustached bat fall into three main types: short (16 of 136), band (34 of 136), and long (29 of 136) pass. The remaining 51 neurons showed no selectivity for the duration of sounds. The distribution of best durations wa...
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Frequency tuning, temporal response pattern and latency properties of inferior colliculus neurons were investigated in the big fruit-eating bat, Artibeus jamaicensis. Neurons having best frequencies between 48-72 kHz and between 24-32 kHz are overrepresented. The inferior colliculus neurons had either phasic (consisting in only one response cycle a...
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We recorded the echolocation behavior of the molossid bat Mormopterus minutus, a species that uses a plastic call inventory. During its foraging activity, M. minutus searches for insects emitting rather long and narrow-band echolocation calls. Search call design however, can vary noticeably even in a continuous foraging pass. While echolocating in...
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The extent of the auditory cortex in the bat Molossus molossus was electrophysiologically investigated. Best frequencies and minimum thresholds of neural tuning curves were analyzed to define the topography of the auditory cortex. The auditory cortex encompasses an average cortical surface area of 5mm(2). Characteristic frequencies are tonotopicall...
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We studied the echolocation calls emitted by Phyllops falcatus (Chiroptera: Phyllostomidae) during foraging, in the field and in the lab. Calls emitted in free flight, in a more or less uncluttered situation, were about 4.5 ms (up to 5.3 ms) long and characterized by a sweep of the first harmonic (= fundamental) from ca. 73 kHz down to about 23 kHz...
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Unlike any other foraging phyllostomid bat studied to date, Poey's flower bats (Phyllonycteris poeyi-Phyllostomidae) emit relatively long (up to 7.2 ms), intense, single-harmonic echolocation calls. These calls are readily detectable at distances of at least 15 m. Furthermore, the echolocation calls contain only the first harmonic, which is usually...
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We studied the echolocation calls of Brachyphylla nana (Chiroptera: Phyllostomidae) under laboratory conditions. Echolocation calls of B. nana are signals of short duration, containing 2 to 4 harmonics of downward frequency modulation overlapping in frequency. Echolocation calls were recorded during orientation and approach behavior of bats flying...
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Echolocation calls emitted by the 4 species of Cuban mormoopid bats were compared to determine vocal signatures that enable identification of each species in the field during their evening exodus. Echolocation calls produced by Mormoops blainvilli are downward frequency-modulated (FM) signals in the range of 68.4– 52.5 kHz. Echolocation calls emitt...
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Behavioral audiograms of Artibeus jamaicensis and Eptesicus fuscus are characterized by two threshold minima separated by a threshold maximum at 40 kHz, for A. jamaicensis, and 45 kHz, for E. fuscus [Koay, G., Heffner, H.E., Heffner R.S., 1997. Audiogram of the big brown bat (Eptesicus fuscus). Hear. Res. 105, 202-210; Heffner, R.S., Koay, G., Heff...
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We studied the echolocation behaviour of Nycticeius cubanus in the field in western Cuba. During hunting, N. cubanus search for insects emitting cries that sweep from 80 to 40 kHz in 4 to 12 ms. Search call characteristics correlate with the clutter structure of the hunting areas. Bats hunting in an uncluttered space broadcast longer and narrower s...
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While searching for prey, Molossus molossus broadcasts narrow-band calls of 11.42 ms organized in pairs of pulses that alternate in frequency. The first signal of the pair is at 34.5 kHz, the second at 39.6 kHz. Pairs of calls with changing frequencies were only emitted when the interpulse intervals were below 200 ms. Maximum duty cycles during sea...
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Echolocation calls were recorded from Pteronotus quadridens flying in the field and in an enclosed space. In the field, search calls contained 1 or 2 harmonics. Patterns of call design show a segment of quasi-constant frequency (QCF2nd-harmonic at 81–84 kHz), followed by a downward frequency-modulated (FM) component. The 2nd harmonic was always mor...

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Project (1)
Project
The goal of this project is to identify behavioral and neurophysiological adaptations that facilitate the classification and identification of obstacles and targets by biosonar. We utilize behavioral assays to test hypotheses about how bats interpret echoes while inspecting and making decisions about a target. We use neurophysiological tools to examine how important acoustic cues embedded within echoes are encoded in the auditory system and reunited to form a perception of the object.