Perception of Vocal Tract Resonances by Whooping Cranes Grus americana

Although formants (vocal tract resonances) can often be observed in avian vocalizations, and several bird species have been shown to perceive formants in human speech sounds, no studies have examined formant perception in birds' own species-specific calls. We used playbacks of computer-synthesized crane calls in a modified habituation—dishabituation paradigm to test for formant perception in whooping cranes ( Grus americana ). After habituating birds to recordings of natural contact calls, we played a synthesized replica of one of the habituating stimuli as a control to ensure that the synthesizer worked adequately; birds dishabituated in only one of 13 cases. Then, we played the same call with its formant frequencies shifted. The birds dishabituated to the formant-shifted calls in 10 out of 12 playbacks. These data suggest that cranes perceive and attend to changes in formant frequencies in their own species-specific vocalizations, and are consistent with the hypothesis that formants can provide acoustic cues to individuality and body size.     

Retraction of the mobile descended larynx during groaning enables fallow bucks (Dama dama) to lower their formant frequencies

A permanently descended larynx is found in humans and several other species of mammals. In addition to this, the larynx of species such as fallow deer is mobile and in males it can be retracted during vocalization. The most likely explanation for the lowered retractable larynx in mammals is that it serves to exaggerate perceived body size (size exaggeration hypothesis) by decreasing the formant frequencies of calls. In this study, we quantified for the first time the elongation of the vocal tract in fallow bucks during vocalization. We also measured the effect of this vocal tract length (VTL) increase on formant frequencies (vocal tract resonances) and formant dispersion (spacing of formants). Our results show that fallow bucks increase their VTL on average by 52% during vocalization. This elongation resulted in strongly lowered formant frequencies and decreased formant dispersion. There were minimal changes to formants 1 and 2 (−0.91 and +1.9%, respectively) during vocal tract elongation, whereas formants 3, 4 and 5 decreased substantially: 18.9, 10.3 and 13.6%, respectively. Formant dispersion decreased by 12.4%. Formants are prominent in deer vocalizations and are used by males to gain information on the competitive abilities of signallers. It remains to be seen whether females also use the information that formants contain for assessing male quality before mating.     

Formant Frequencies are Acoustic Cues to Caller Discrimination and are a Weak Indicator of the Body Size of Corncrake Males

Source–filter theory assumes that calls are generated by a vocal source and are subsequently filtered by the vocal tract. The air in the vocal tract vibrates preferentially at certain resonant frequencies, called formants. Formant frequencies can be a good indicator of the caller's characteristics, such as sex, age, body size or individual identity. Although source–filter theory was originally proposed for mammals, formants are also observed in birds, and some bird species have been shown to perceive formants. In this study, we evaluated the hypotheses that formant frequencies (1) are an indicator of body size and (2) can be used for individual discrimination by a nocturnal bird species, the corncrake (Crex crex). We analysed calls of 104 males from Poland and the Czech Republic. Linear regression models showed that the males with a longer head (including the bill length) had a significantly lower formant dispersion and lower fourth and fifth formant frequencies. However, we found no significant relationships between body weight and any filter‐related acoustic measurement. The formant frequencies had smaller within‐ than between‐individual coefficients of variation. This characteristic of the formant frequencies implies a high potential for individual coding. A discriminant function analysis correctly assigned 94.8% of the calls to the caller based on formants from second to fifth. Our results indicated that the formant frequencies are a weak indicator of the body size of the sender in the corncrake. However, even weak dependence between body size and acoustic properties of signal may be important in natural selection process. Alternatively, such a weak dependence may be observed, because receivers ignore the acoustical, formant‐based cues of body size. Simultaneously, the formants might potentially provide acoustic cues to individual discrimination and could be used to census and monitoring tasks.     

Red deer stags use formants as assessment cues during intrasexual agonistic interactions

While vocal tract resonances or formants are key acoustic parameters that define differences between phonemes in human speech, little is known about their function in animal communication. Here, we used playback experiments to present red deer stags with re-synthesized vocalizations in which formant frequencies were systematically altered to simulate callers of different body sizes. In response to stimuli where lower formants indicated callers with longer vocal tracts, stags were more attentive, replied with more roars and extended their vocal tracts further in these replies. Our results indicate that mammals other than humans use formants in vital vocal exchanges and can adjust their own formant frequencies in relation to those that they hear.     

Visualizing Sound Emission of Elephant Vocalizations: Evidence for Two Rumble Production Types

Recent comparative data reveal that formant frequencies are cues to body size in animals, due to a close relationship between formant frequency spacing, vocal tract length and overall body size. Accordingly, intriguing morphological adaptations to elongate the vocal tract in order to lower formants occur in several species, with the size exaggeration hypothesis being proposed to justify most of these observations. While the elephant trunk is strongly implicated to account for the low formants of elephant rumbles, it is unknown whether elephants emit these vocalizations exclusively through the trunk, or whether the mouth is also involved in rumble production. In this study we used a sound visualization method (an acoustic camera) to record rumbles of five captive African elephants during spatial separation and subsequent bonding situations. Our results showed that the female elephants in our analysis produced two distinct types of rumble vocalizations based on vocal path differences: a nasally- and an orally-emitted rumble. Interestingly, nasal rumbles predominated during contact calling, whereas oral rumbles were mainly produced in bonding situations. In addition, nasal and oral rumbles varied considerably in their acoustic structure. In particular, the values of the first two formants reflected the estimated lengths of the vocal paths, corresponding to a vocal tract length of around 2 meters for nasal, and around 0.7 meters for oral rumbles. These results suggest that African elephants may be switching vocal paths to actively vary vocal tract length (with considerable variation in formants) according to context, and call for further research investigating the function of formant modulation in elephant vocalizations. Furthermore, by confirming the use of the elephant trunk in long distance rumble production, our findings provide an explanation for the extremely low formants in these calls, and may also indicate that formant lowering functions to increase call propagation distances in this species''.     

Variable asymmetry and resonance in the avian vocal tract: a structural basis for individually distinct vocalizations

The social vocalizations of the oilbird (Steatornis caripensis) frequently have their acoustic energy concentrated into 3 prominent formants which appear to arise from the filter properties of their asymmetrical vocal tract with its bronchial syrinx. The frequency of the second and third formants approximate the predicted fundamental resonances of the unequal left and right cranial portions of each primary bronchus, respectively. Reversibly plugging either bronchus eliminates the corresponding formant. The first formant may arise in the trachea. The degree of vocal tract asymmetry varies between individuals, endowing them with different formant frequencies and providing potential acoustic cues by which individuals of this nocturnal, cave dwelling species may recognize each other in their dark, crowded colonies.     

Phonation in the Orange-winged Amazon parrot,Amazona amazonica

Summary The syrinx of the Orange-winged Amazon parrot includes two external tympaniform membranes thought to be involved in sound production. The position of these membranes at the confluence of the bronchial and tracheal lumina requires that during phonation they be driven by a single column of air and by its attending turbulence patterns. Because of this anatomical arrangement, the phonatory output of either right or left syringeal half is grossly affected by denervation of the ipsilateral or contralateral syringial muscles. Following unilateral syringeal denervation the unbalanced oscillation of the two external tympaniform membranes generates noise. Form this we may infer that normally the parrot syrinx acts as a unitary sound source. Syringeal innervation is provided by the tracheosyringealis branch of the hypoglossus nerve. Each tracheosyringealis innervates both syringeal halves. Section of either the right or left tracheosyringealis leads to a minor and temporary change in the structure of vocalization. One week after the operation the vocalizations are delivered as pre-operatively. There is no indication of either right or left hypoglossal dominance in the phonatory control of the parrot syrinx. Other observations presented here are used to speculate on the possible role of the parrot tongue in altering the resonating properties of the nasopharyngeal space and generating speech like formants.     

Vocal Tract Morphology Determines Species-Specific Features in Vocal Signals of Lemurs (Eulemur)

The source-filter theory describes vocal production as a two-stage process involving the generation of a sound source, with its own spectral structure, which is then filtered by the resonant properties of the vocal tract. This theory has been successfully applied to the study of animal vocal signals since the 1990s. As an extension, models reproducing vocal tract resonance can be used to reproduce formant patterns and to understand the role of vocal tract filtering in nonhuman vocalizations. We studied three congeneric lemur species —Eulemur fulvus, E. macaco, E. rubriventer— using morphological measurements to build computational models of the vocal tract to estimate formants, and acoustic analysis to measure formants from natural calls. We focused on call types emitted through the nose, without apparent articulation. On the basis of anatomical measurements, we modeled the vocal tract of each species as a series of concatenated tubes, with a cross-sectional area that changed along the tract to approximate the morphology of the larynx, the nasopharyngeal cavity, the nasal chambers, and the nostrils. For each species, we calculated the resonance frequencies in 2500 randomly generated vocal tracts, in which we simulated intraspecific length and size variation. Formant location and spacing showed significant species-specific differences determined by the length of the vocal tract. We then measured formants of a set of nasal vocalizations (“grunts”) recorded from captive lemurs of the same species. We found species-specific differences in the natural calls. This is the first evidence that morphology of the vocal tract is relevant in generating filter-related acoustic cues that potentially provide receivers with information about the species of the emitter.     

Are men better than women at acoustic size judgements?

Formants are important phonetic elements of human speech that are also used by humans and non-human mammals to assess the body size of potential mates and rivals. As a consequence, it has been suggested that formant perception, which is crucial for speech perception, may have evolved through sexual selection. Somewhat surprisingly, though, no previous studies have examined whether sexes differ in their ability to use formants for size evaluation. Here, we investigated whether men and women differ in their ability to use the formant frequency spacing of synthetic vocal stimuli to make auditory size judgements over a wide range of fundamental frequencies (the main determinant of vocal pitch). Our results reveal that men are significantly better than women at comparing the apparent size of stimuli, and that lower pitch improves the ability of both men and women to perform these acoustic size judgements. These findings constitute the first demonstration of a sex difference in formant perception, and lend support to the idea that acoustic size normalization, a crucial prerequisite for speech perception, may have been sexually selected through male competition. We also provide the first evidence that vocalizations with relatively low pitch improve the perception of size-related formant information.     

The anatomy, physiology, acoustics and perception of speech: essential elements in analysis of the evolution of human speech

Inferences on the evolution of human speech based on anatomical data must take into account its physiology, acoustics and perception. Human speech is generated by the supralaryngeal vocal tract (SVT) acting as an acoustic filter on noise sources generated by turbulent airflow and quasi-periodic phonation generated by the activity of the larynx. The formant frequencies, which are major determinants of phonetic quality, are the frequencies at which relative energy maxima will pass through the SVT filter. Neither the articulatory gestures of the tongue nor their acoustic consequences can be fractionated into oral and pharyngeal cavity components. Moreover, the acoustic cues that specify individual consonants and vowels are “encoded”, i.e., melded together. Formant frequency encoding makes human speech a vehicle for rapid vocal communication. Non-human primates lack the anatomy that enables modern humans to produce sounds that enhance this process, as well as the neural mechanisms necessary for the voluntary control of speech articulation. The specific claims of Duchin (1990) are discussed.     

Spectrographic analysis points to source–filter coupling in rutting roars of Iberian red deer

Source–filter coupling is the rarest acoustic phenomenon not only in Iberian red deer, but in any mammal. In most mammals, sound production can be well described in the framework of source–filter theory. The vocal output is the result of combined work of the larynx (the source) and of the supralaryngeal vocal tract (the filter). The source–filter theory suggests the independence of source and filter. Thus, vocal tract filtering should not affect the fundamental frequency (f0) of the sound created in the larynx. Spectrographically, the source is mostly characterized by the f0 and its harmonics, while the filter by the vocal tract resonances, i.e., formant frequencies. Nevertheless, a non-independent (coupled) source and filter can be proposed when the vocal folds start oscillating at one of the formant frequencies. Coupling between source and filter has been found in human singers and predicted for red deer Cervus elaphus by a computer modeling approach. This study describes different modes of phonation in a natural bout of rutting calls of Iberian red deer Cervus elaphus hispanicus and the transition from a chaotic mode to a probable source–filter coupling mode. This phenomenon might be involved in the production of extremely high-frequency bugles of North American and Asian subspecies of C. elaphus.     

Individual Acoustic Variation in Fallow Deer (Dama dama) Common and Harsh Groans: A Source-Filter Theory Perspective

Mammals are able to distinguish conspecifics based on vocal cues, and the acoustic structure of mammal vocalizations is directly affected by the anatomy and action of the vocal apparatus. However, most studies investigating individual patterns in acoustic signals do not consider a vocal production‐based perspective. In this study, we used the source‐filter model of vocal production as a basis for investigating the acoustic variability of fallow deer groans. Using this approach, we quantified the potential of each acoustic component to carry information about individual identity. We also investigated if cues to individual identity carry over among the two groan types we describe: common and harsh groans. Using discriminant function analysis, we found that variables related to the fundamental frequency contour and the minimum frequencies of the highest formants contributed most to the identification of a given common groan. Common groans were individually distinctive with 36.6% (53.6% with stepwise procedure) of groans assigned to the correct individual. This level of discrimination is approximately six times higher than that predicted by chance. In addition, univariate anova s showed significant inter‐individual variation in the minimum formant frequencies when common and harsh groans were combined, suggesting that some information about individuality is shared between groan types. Our results suggest that the sound source and the vocal tract resonances act together to determine groan individuality and that enough variation exists to potentially allow individual recognition based on groans.     

Nasal and oral calls in mother and young trunk-nosed saiga antelopes,Saiga tatarica

The trunk-like nose of the saiga antelope Saiga tatarica is a striking example of an exaggerated trait, assumed to having evolved as a dust filter for inhaled air. In addition, it functions to elongate the vocal tract in harem saiga males for producing low-formant calls that serve as a cue to body size for conspecifics. This study applies the source–filter theory to the acoustics of nasal, oral and nasal-and-oral calls that were recorded from a captive herd of 24 mother and 32 neonate saigas within the first 10 days postpartum. Anatomical measurements of the nasal and oral vocal tracts of two specimens (one per age class) helped to establish the settings for the analysis of formants. In both mother and young, the lower formants of nasal calls/call parts were in agreement with the source–filter theory, which suggests lower formants for the longer nasal vocal tract than for the shorter oral vocal tract. Similar fundamental frequencies of the nasal and oral parts of nasal-and-oral calls were also in agreement with the source–filter theory, which postulates the independence of source and filter. However, the fundamental frequency was higher in oral than in nasal calls, probably due to the higher emotional arousal during the production of oral calls. We discuss production mechanisms and the ontogeny of formant patterns of oral and nasal calls among bovid and cervid species with and without a trunk-like nose.     

Geographical variation in the vocalizations of the suboscine Thorn‐tailed Rayadito Aphrastura spinicauda

Structural variation in acoustic signals may be related either to the factors affecting sound production such as bird morphology, or to vocal adaptations to improve sound transmission in different environments. Thus, variation in acoustic signals can influence intraspecific communication processes. This will ultimately influence divergence in allopatric populations. The study of geographical variation in vocalizations of suboscines provides an opportunity to compare acoustic signals from different populations, without additional biases caused by song learning and cultural evolution typical of oscines. The aim of this study was to compare vocalizations of distinct populations of a suboscine species, the Thorn‐tailed Rayadito. Four types of vocalizations were recorded in five populations, including all three currently accepted subspecies. Comparisons of each type of vocalization among the five populations showed that some variation existed in the repetitive trill, whereas no differences were found among alarm calls and loud trills. Variation in repetitive trills among populations and forest types suggests that sound transmission is involved in vocal differences in suboscines. Acoustic differences are also consistent with distinguishing subspecies bullocki from spinicauda and fulva, but not the two latter subspecies from each other. Our results suggest that the geographical differentiation in vocalizations observed among Thorn‐tailed Rayadito populations is likely to be a consequence of different ecological pressures. Therefore, incipient genetic isolation of these populations is suggested, based on the innate origin of suboscine vocalizations.     

Children's development of self-regulation in speech production

Species-specific vocalizations fall into two broad categories: those that emerge during maturation, independent of experience, and those that depend on early life interactions with conspecifics. Human language and the communication systems of a small number of other species, including songbirds, fall into this latter class of vocal learning. Self-monitoring has been assumed to play an important role in the vocal learning of speech and studies demonstrate that perception of your own voice is crucial for both the development and lifelong maintenance of vocalizations in humans and songbirds. Experimental modifications of auditory feedback can also change vocalizations in both humans and songbirds. However, with the exception of large manipulations of timing, no study to date has ever directly examined the use of auditory feedback in speech production under the age of 4. Here we use a real-time formant perturbation task to compare the response of toddlers, children, and adults to altered feedback. Children and adults reacted to this manipulation by changing their vowels in a direction opposite to the perturbation. Surprisingly, toddlers' speech didn't change in response to altered feedback, suggesting that long-held assumptions regarding the role of self-perception in articulatory development need to be reconsidered.     

Vocal-tract resonances as indexical cues in rhesus monkeys

Vocal-tract resonances (or formants) are acoustic signatures in the voice and are related to the shape and length of the vocal tract. Formants play an important role in human communication, helping us not only to distinguish several different speech sounds [1], but also to extract important information related to the physical characteristics of the speaker, so-called indexical cues. How did formants come to play such an important role in human vocal communication? One hypothesis suggests that the ancestral role of formant perception--a role that might be present in extant nonhuman primates--was to provide indexical cues [2-5]. Although formants are present in the acoustic structure of vowel-like calls of monkeys [3-8] and implicated in the discrimination of call types [8-10], it is not known whether they use this feature to extract indexical cues. Here, we investigate whether rhesus monkeys can use the formant structure in their "coo" calls to assess the age-related body size of conspecifics. Using a preferential-looking paradigm [11, 12] and synthetic coo calls in which formant structure simulated an adult/large- or juvenile/small-sounding individual, we demonstrate that untrained monkeys attend to formant cues and link large-sounding coos to large faces and small-sounding coos to small faces-in essence, they can, like humans [13], use formants as indicators of age-related body size.     

The F1-F2 vowel chart for Czech whispered vowels a, e, i, o, u

Aim: The aim of this contribution is to present the formant chart of the Czech vowels a, e, i, o, u and show that this can be achieved by means of digital methods of sound processing. Method: A group of 35 Czech students of the Pedagogical Faculty of Palacky University was tested and a record of whispered vowels was taken from each of them. The record was digitalized and processed by the Discrete Fourier Trasform. The result is the power spectrum of the individual vocals - the graphic output consists of a plot of the relative power of individual frequencies in the original sound. The values of the first two maxima which represent the first and the second formants were determined from the graph. The values were plotted on a formant chart. Results: Altogether, 175 spectral analyses of individual vowels were performed. In the resulting power spectrum, the first and the second formant frequencies were identified. The first formant was plotted against the second one and pure vocal formant regions were identified. Conclusion: Frequency bands for the Czech vowel "a" were circumscribed between 850 and 1150 Hz for first formant (F1) and between 1200 and 2000 Hz for second formant (F2). Similarly, borders of frequency band for vowel "e" they were 700 and 950 Hz for F1 and 1700 and 3000 Hz for F2. For vowel "i" 300 and 450 Hz for F1 and 2000 and 3600 Hz for F2, for vowel "o" 600 and 800 Hz for F1 and 600 and 1400 Hz for F2, for vowel "u" 100 and 400 Hz for F1 and 400 and 1200 Hz for F2. Discussion: At low frequencies it is feasible to invoke the source-filter model of voice production and associate vowel identity with frequencies of the first two formants in the voice spectrum. On the other hand, subject to intonation, singing or other forms of exposed voice (such as emotional speech, focused speech), the formant regions tend to spread. In spectral analysis other frequencies dominate, so specific formant frequency bands are not easily recognizable. Although the resulting formant map is not much different from the formant map of Peterson, it carries basic information about specific Czech vowels. The results may be used in further research and in education.     

鸟类鸣声与个体适合度关系的研究进展

鸣声蕴藏着丰富的生物学信息,是鸟类间信息交流最主要的方式之一。本文综述了鸟类鸣声行为与包括个体状态(体征、激素水平和健康状况)、社会等级及繁殖(性选择和成效)在内的个体适合度关系的研究进展。文章总结发现,鸟类的鸣声水平与单一体征参数关系的研究结果不稳定,鸣声可能受个体内部的多种激素调控,并与个体的社会等级有直接关系。雌雄个体鸣声均与繁殖有一定相关性,但双亲鸣声行为策略存在差异。鸣声对繁殖适合度的影响受到其他因素如物种、婚配制度等因素的影响。鸟类鸣声代表的生物学信息是个体身体质量的综合体现,与鸟类个体适合度的关系较为复杂。为解释鸣声所代表的生物学信息,需要从适合度的多个角度(社会等级、身体状况和繁殖情况等)来考虑多种鸣声参数。     

Measurement of grey parrot (Psittacus erithacus) trachea via magnetic resonance imaging,dissection, and electron beam computed tomography

To produce a model to explain the acoustic properties of human speech sounds produced by Grey parrots (Psittacus erithacus) and to compare these properties across species (e.g., with humans, other psittacine and nonpsittacine mimics), researchers need adequate measurements of the chambers that constitute the parrot vocal tract. Various methods can provide such data. Here we compare results for tracheal measurements provided by a) magnetic resonance imaging (MRI) of a live bird, b) caliper measurements of four preserved specimens, and c) electron beam computed tomography (EBCT) of three of these preserved specimens. We find that EBCT scans provide data that correspond to the inner area of the dissected trachea, whereas MRI results correspond to area measurements that include tracheal ring thickness. We briefly discuss how these data may predict formant values for Grey parrot reproduction of human vowels. Our results suggest how noninvasive techniques can be used for cross-species comparisons, including the coevolution of structure and function in avian mimicry. J. Morphol. 238:81–91, 1998. © 1998 Wiley-Liss, Inc.