| The Perilous Serenades of Túngara Frogs |
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| The Michael Ryan Lab at the University of Texas studies the effect of sexual preference on the communication systems of tungara frogs, investigating the evolutionary advantages and costs of different call behaviors.
Dr. Ryan used SIGNAL to generate a set of precisely varied synthetic male frog calls and played these back to females. Observed phonotactic behavior showed that females favor call complexity and suggested their role in shaping male call behavior. Mike then presented a graded set of frog stimuli to frog-eating bats and showed that the call complexity that attracts females also makes the callers acoustically easier to locate as prey. In another experiment (see the paper), the Ryan lab used a SIGNAL program to dynamically vary the presentation of male frog stimuli in order to study male-male phonotaxis. The program presented calls at specific temporal and spatial points determined in real-time by the researcher based on the response of the subject. |
| Increasing Cattle Grazing Efficiency |
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| William Clapham of the U.S. Department of Agriculture, in collaboration with Engineering Design, is using SIGNAL to develop a system to measure the forage consumed by free-grazing beef cattle. The project goal is to model and increase free-grazing efficiency as an ecological and economic alternative to feed-lot beef.
The SIGNAL-based system automatically detects, classifies, and quantifies streaming acoustic recordings of biting and chewing sounds. The SIGNAL Event Detector uses spectral and temporal analysis to distinguish biting (consumptive) from chewing events and to shield both from environmental and other non-target sounds. SIGNAL's programmability is used to automatically analyze thousands of events to dramatically increase the statistical resolution of the results. The classification system has proved 95% accurate relative to trained human observers. |
| Signature Whistle Learning in Bottlenose Dolphins |
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| Vincent Janik at the University of St. Andrews studies the relationship between vocal communication systems and social interaction. He investigates the environmental constraints that influence vocal communication and the cognitive skills that address those constraints. He works on vocal communication in the bottlenose dolphins, which combine vocal learning with complex cognitive skills.
Dr. Janik used SIGNAL to establish that bottlenose dolphins develop individual signature whistles containing identity information independent of the caller’s "voice" features. Dr. Janik used the SIGNAL tonal sound synthesis model to separate and extract the whistle's complete spectral behavior from all other vocal features, then synthesize new "voice-free" playback calls based on spectral behavior alone. See the dramatic figure in the paper below. Dr. Janik then showed experimentally that wild test subjects responded to identity information even in the synthetic whistles with all voice features removed. |
| Birdsongs Sound Sweeter Because Throats Filter Out Messy Overtones |
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| The Rod Suthers lab at Indiana University studies the neuroethology of acoustic communication with a focus on the physiology of song production in songbirds employing complex vocal communication in which learning plays an important role. Research areas include the development and coordination of motor patterns during vocal learning; vocal practice and critical developmental periods in song learning; and functional neural lateralization in the control of behavior.
In order to study the motor constraints and processes of birdsong production, Dr. Suthers used SIGNAL to analyze detailed multi-channel, real-time recordings of the acoustical and physiological variables of sound production. These include the acoustical signal, mechanical components of sound production such as flow velocities in the bird's dual syrinxes, physiological variables and even real-time radiographic imagery of the bird during song production, as shown in the figure. Among other findings, Dr. Suthers discovered that songbirds can dynamically tune their vocal tracts to the fundamental frequency of their song, dramatically increasing acoustic output and eliminating potentially distracting harmonic overtones by operating their vocal mechanism as an acoustical resonator. *Video supplement from "Songbirds tune their vocal tracts to the fundamental frequency of their song", Riede, Suthers, Fletcher and Blevins 2006. PNAS 103:5543-5548 |
| The Love Songs of Free-Tailed Bats |
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| Kirsten Bohn at the University of Texas studies the production, perception and evolution of songs produced by Brazilian free-tailed bats. Her work incorporates field work, lab experiments, genetic analyses and playback experiments.
Studying song, phrase and syllable structure in mating sounds across two widely separated colonies in Texas, Dr. Bohn found stereotypy in the lexicon of both syllables and phrases across the colonies; variation in song and phrase construction among individuals; and the presence of phrase-order rules. She concluded that free-tailed bat songs are composed of highly stereotyped phrases hierarchically organized by a common set of syntactical rules, suggesting a song structure found in birds but rare in mammals. Dr. Bohn used SIGNAL's programmability to automatically analyze the inter-syllable intervals of 19,614 syllables! |
| Development and Localization of Brain Function |
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Click figure to hear sound of chicken, quail and quail-chicken chimera |
| Evan Balaban at McGill University studies the development and localization of brain function. Dr. Balaban successfully transplanted brain cells from quail to chicken embryos, then classified two behaviors in the resulting "chimeras" – sound production and associated head movement – as quail-like vs. chicken-like. Although the two behaviors are tightly integrated in normal chickens, by transplanting different brain areas, Dr. Balaban found these behaviors spatially localized and functionally independent.
Dr. Balaban used SIGNAL to acquire simultaneous data streams from an acoustic microphone and the x,y outputs from a video tracking device. Custom SIGNAL programs then extracted essential spectro-temporal acoustic behavior and motion characteristics. Results showed that one transplant location (midbrain) transferred only vocal behavior while the other location (brainstem) transferred only motion behavior. See the figure and click to play successive sounds of normal chicken, normal quail, and quail-sounding chimera. The results support a model of brain organization in which a "higher" brain area coordinates the diverse components of a complex act performed by "lower" brain areas that manage the fine motor control of individual components such as vocal behavior and head movement. |
| Doppler Shift Compensation in Echolocating Horseshoe Bats |
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| Walter Metzner at UCLA studies auditory feedback control in echolocating greater horseshoe (Rhinolophus) bats. These bats compensate for Doppler-shift frequency variation in the return echolocation signal caused by their flight speed. This "Doppler-shift compensation" behavior maintains the return signal within the bat's spectrally narrow auditory reception band. Compensation behavior has been found accurate to a few hundred Hz on an 80,000 Hz signal.
In collaboration with Dr. Metzner, Engineering Design developed an ultrasonic hardware processor to receive an echolocation signal and return it in real-time with functionally controllable variable delay and frequency shift (accurate to 1 Hz out of 90,000 Hz) in order to simulate Doppler-shift effects. SIGNAL performed high-speed data acquisition to acquire echolocation and synthetic return signals, while issuing triggers to an external neurophysiology data acquisition system to synchronize neural and acoustic data. |