High-Resolution,Non-Invasive Imaging of Upper Vocal Tract Articulators Compatible with Human Brain Recordings

A complete neurobiological understanding of speech motor control requires determination of the relationship between simultaneously recorded neural activity and the kinematics of the lips, jaw, tongue, and larynx. Many speech articulators are internal to the vocal tract, and therefore simultaneously tracking the kinematics of all articulators is nontrivial—especially in the context of human electrophysiology recordings. Here, we describe a noninvasive, multi-modal imaging system to monitor vocal tract kinematics, demonstrate this system in six speakers during production of nine American English vowels, and provide new analysis of such data. Classification and regression analysis revealed considerable variability in the articulator-to-acoustic relationship across speakers. Non-negative matrix factorization extracted basis sets capturing vocal tract shapes allowing for higher vowel classification accuracy than traditional methods. Statistical speech synthesis generated speech from vocal tract measurements, and we demonstrate perceptual identification. We demonstrate the capacity to predict lip kinematics from ventral sensorimotor cortical activity. These results demonstrate a multi-modal system to non-invasively monitor articulator kinematics during speech production, describe novel analytic methods for relating kinematic data to speech acoustics, and provide the first decoding of speech kinematics from electrocorticography. These advances will be critical for understanding the cortical basis of speech production and the creation of vocal prosthetics.     

Vocal Tract Articulation in Zebra Finches

Background

Birdsong and human vocal communication are both complex behaviours which show striking similarities mainly thought to be present in the area of development and learning. Recent studies, however, suggest that there are also parallels in vocal production mechanisms. While it has been long thought that vocal tract filtering, as it occurs in human speech, only plays a minor role in birdsong there is an increasing number of studies indicating the presence of sound filtering mechanisms in bird vocalizations as well.

Methodology/Principal Findings

Correlating high-speed X-ray cinematographic imaging of singing zebra finches (Taeniopygia guttata) to song structures we identified beak gape and the expansion of the oropharyngeal-esophageal cavity (OEC) as potential articulators. We subsequently manipulated both structures in an experiment in which we played sound through the vocal tract of dead birds. Comparing acoustic input with acoustic output showed that OEC expansion causes an energy shift towards lower frequencies and an amplitude increase whereas a wide beak gape emphasizes frequencies around 5 kilohertz and above.

Conclusion

These findings confirm that birds can modulate their song by using vocal tract filtering and demonstrate how OEC and beak gape contribute to this modulation.     

Vocal Ontogeny in Neotropical Singing Mice (Scotinomys)

Isolation calls produced by dependent young are a fundamental form of communication. For species in which vocal signals remain important to adult communication, the function and social context of vocal behavior changes dramatically with the onset of sexual maturity. The ontogenetic relationship between these distinct forms of acoustic communication is surprisingly under-studied. We conducted a detailed analysis of vocal development in sister species of Neotropical singing mice, Scotinomys teguina and S. xerampelinus. Adult singing mice are remarkable for their advertisement songs, rapidly articulated trills used in long-distance communication; the vocal behavior of pups was previously undescribed. We recorded 30 S. teguina and 15 S. xerampelinus pups daily, from birth to weaning; 23 S. teguina and 11 S. xerampelinus were recorded until sexual maturity. Like other rodent species with poikilothermic young, singing mice were highly vocal during the first weeks of life and stopped vocalizing before weaning. Production of first advertisement songs coincided with the onset of sexual maturity after a silent period of ≧2 weeks. Species differences in vocal behavior emerged early in ontogeny and notes that comprise adult song were produced from birth. However, the organization and relative abundance of distinct note types was very different between pups and adults. Notably, the structure, note repetition rate, and intra-individual repeatability of pup vocalizations did not become more adult-like with age; the highly stereotyped structure of adult song appeared de novo in the first songs of young adults. We conclude that, while the basic elements of adult song are available from birth, distinct selection pressures during maternal dependency, dispersal, and territorial establishment favor major shifts in the structure and prevalence of acoustic signals. This study provides insight into how an evolutionarily conserved form of acoustic signaling provides the raw material for adult vocalizations that are highly species specific.     

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.     

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.     

Biomechanical and Morphometric Differences in Triticum aestivum Seedlings Differing in Rht Gene-Dosage

Biomechanical and morphometric comparisons among coleoptilesfrom wheat seedlings differing in Rht gene-dosage (Rht = 0,2, 4 doses) are presented in an effort to evaluate the influenceof Rht on the mechanics of soil penetration by this organ. Rhtis known to reduce seedling establishment compared to the wildtype. Data from 3–7-day-old seedlings indicate that Rhtreduces tissue elastic modulus E, increases the second momentof area I, and decreases the slenderness ratio (l/r) of coleoptiles.Rht-relatedchanges in E and I are such that the flexural stiffness of coleoptilesfrom Rht plants does not differ significantly from the wildtype-hence the growing coleoptiles of all three genotypes haveequivalent biomechanical capacity to penetrate the soil. Rhtreduction of coleoptile slenderness ratios confers a capacityto safely sustain higher axial compressive loads compared tocoleoptiles with equivalent flexural stiffness but higher ratios.However, wild type seedlings produce longer coleoptiles andlonger subcrown internodes than Rht seedlings. Longer coleoptilesdeliver the crown node closer to the top of the soil beforethe crown node extends beyond the lateral confinement of thecoleoptile. This reduces the potential for buckling of the subcrowninternode and leaves due to the compressive loading of soil.Rht affects a variety of mechanical features whose influenceis dependent upon the stage of seedling growth and the degreeof soil compaction. However, at equivalent depths of burialwhich exceed the maximum length of coleoptiles and moderatesoil compaction, Rht is biomechanically disadvantageous to seedlingestablishment. Wheat, germination, biomechanics, Rht-gene     

Variation in Vocal Performance in the Songs of a Wood-Warbler: Evidence for the Function of Distinct Singing Modes

Male North American wood‐warblers (family Parulidae) subdivide their song repertoires into two different categories, or modes, of singing (first and second category songs). These two modes are thought to be specialized for interacting with females and males, although the data are inconclusive. I conducted an acoustic analysis of the song types used by yellow warblers (Dendroica petechia) for type I (first category) and type II (second category) singing to ask whether there are consistent structural differences between them which could provide insight into how they might function as separate signals. I found that type I songs are performed closer to the upper boundary of a song performance limit, measured in terms of the difficulty of production, compared with type II songs. By contrast, the performance of specific song types did not depend on whether they were used for type I singing vs. type II singing by different males. In addition, type I songs had a greater amplitude increase across the first two syllables compared with type II songs. There was no relationship between the performance of type I or type II songs and male condition. These results suggest that wood‐warblers might subdivide their song repertoire into distinct categories to highlight the relative vocal performance of their songs.     

Morphometric and Stereologic Analysis of Chlorella vulgaris Under Heterotrophic Growth Conditions

A computer-supported determination of stereological parameterswas used to study the possible ultrastructural changes of Chlorellavulgaris UAM 101 under photolithotrophic, mixotrophic and photoheterotrophicconditions of growth. Data recording was carried out througha semi-automatic digitizing image analysis system instead ofthe current method of superimposition of an array of short lines. Glucose promoted drastic physiological changes [Martínezand Orús, 1991. Plant Physiology (in press)], which stronglyaffected the size of the cells and volume densities of storagematerials. However, volumetric ratios of the mitochondrion orchloroplast active fraction were not affected by the presenceof glucose, probably indicating that these ratios are characteristicof each species. Cell wall ultrastructure was also analysed and the presenceof sporopollenin demonstrated, in contrast to the thin and sporopollenin-lackingcell wall generally described for Chlorella vulgaris species. Chlorella vulgaris, photoautotrophic, mixotrophic, photoheterotrophic, image analysis, stereology     

Singing Under the Influence: Examining the Effects of Nutrition and Addiction on a Learned Vocal Behavior

The songbird model is widely established in a number of laboratories for the investigation of the neurobiology and development of vocal learning. While vocal learning is rare in the animal kingdom, it is a trait that songbirds share with humans. The neuroanatomical and physiological organization of the brain circuitry that controls learned vocalizations has been extensively characterized, particularly in zebra finches (Taeniopygia guttata). Recently, several powerful molecular and genomic tools have become available in this organism, making it an attractive choice for neurobiologists interested in the neural and genetic basis of a complex learned behavior. Here, we briefly review some of the main features of vocal learning and associated brain structures in zebra finches and comment on some examples that illustrate how themes related to nutrition and addiction can be explored using this model organism.     

Susceptibility of Pseudomonas aeruginosa Urinary Tract Isolates and Influence of Urinary Tract Conditions on Antibiotic Tolerance

Pseudomonas aeruginosa is an opportunistic human pathogen, which can cause severe urinary tract infections (UTIs). Because of the high intrinsic antibiotic resistance of P. aeruginosa and its ability to develop new resistances during antibiotic treatment, these infections are difficult to eradicate. The antibiotic susceptibility of 32 P. aeruginosa isolates from acute and chronic UTIs were analysed under standardized conditions showing 19% multi-drug resistant strains. Furthermore, the antibiotic tolerance of two P. aeruginosa strains to ciprofloxacin and tobramycin was analysed under urinary tract-relevant conditions which considered nutrient composition, biofilm growth, growth phase, and oxygen concentration. These conditions significantly enhance the antibiotic tolerance of P. aeruginosa up to 6000-fold indicating an adaptation of the bacterium to the specific conditions present in the urinary tract. This reversible phenomenon is possibly due to the increased formation of persister cells and is based on iron limitation in artificial urine. The results suggest that the general high antibiotic resistance of P. aeruginosa urinary tract isolates together with the increasing tolerance of P. aeruginosa grown under urinary tract conditions decrease the efficiency of antibiotic treatment of UTIs.     

Anticipatory Posturing of the Vocal Tract Reveals Dissociation of Speech Movement Plans from Linguistic Units

Models of speech production typically assume that control over the timing of speech movements is governed by the selection of higher-level linguistic units, such as segments or syllables. This study used real-time magnetic resonance imaging of the vocal tract to investigate the anticipatory movements speakers make prior to producing a vocal response. Two factors were varied: preparation (whether or not speakers had foreknowledge of the target response) and pre-response constraint (whether or not speakers were required to maintain a specific vocal tract posture prior to the response). In prepared responses, many speakers were observed to produce pre-response anticipatory movements with a variety of articulators, showing that that speech movements can be readily dissociated from higher-level linguistic units. Substantial variation was observed across speakers with regard to the articulators used for anticipatory posturing and the contexts in which anticipatory movements occurred. The findings of this study have important consequences for models of speech production and for our understanding of the normal range of variation in anticipatory speech behaviors.     

Gender Differences in Elements of Human Anterior Commissure and Olfactory Bulb and Tract

To examine whether there were gender differences in the various brain regions, the authors investigated the gender differences in seven element contents of the anterior commissure, mammillary body, and olfactory bulb and tract by direct chemical analysis. After ordinary dissection at Nara Medical University was finished, the anterior commissures, mammillary bodies, and olfactory bulbs and tracts were resected from the cerebra cut at median line. The brain samples were treated with 99.5% ethanol three times to remove lipids. After ashing with nitric acid and perchloric acid, the seven element contents Ca, P, S, Mg, Zn, Fe, and Na were determined by inductively coupled plasma–atomic emission spectrometry. It was found that the Zn content was significantly higher in the anterior commissures of men than in those of women. In the olfactory bulbs and tracts, it was found that the Ca, P, and Zn contents were significantly higher in men than in women. In contrast, no significant difference was found between the mammillary bodies of men and women regarding the seven element contents.     

黑斑侧褶蛙消化道重量及长度的性别和季节差异

消化道是联系脊椎动物能量摄入和能量支出之间关系的纽带,其重量和长度对外界环境具有高度的敏感性和弹性(flexibility)。以黑斑侧褶蛙(Pelophylax nigromaculata)为研究对象,测定了山东聊城地区2012年夏季(16只,8♀/8♂)、秋季(19只,9♀/10♂)及翌年春季(17只,8♀/9♂)其体重、体长、胴体湿重和干重系数、总消化道及各段(食道、胃、小肠和大肠)的湿重、干重和长度系数的性别和季节差异(双因素方差分析),对有性别差异的指标,用单因素方差分析分别比较了雌、雄蛙的季节差异。结果显示,1)雌蛙的体重、体长均高于雄蛙,都在秋季最高,春季或夏季最低;雄蛙的胴体湿重系数高于雌蛙,夏季高于秋季;胴体干重系数既无性别差异,也无季节差异。2)除食道湿重系数无性别差异外,雌蛙总消化道及各段的湿重系数均高于雄蛙;除胃湿重系数无季节差异外,春季或秋季的总消化道及各段的湿重系数都高于夏季;雌蛙的总消化道干重和胃干重系数高于雄蛙,食道、小肠和大肠的干重系数无性别差异,所有的干重系数均无季节性差异。3)除雌蛙的大肠长系数高于雄蛙外,总消化道及各段的长度系数均无性别差异,春季和秋季的总消化道长、食道长及胃长系数均高于夏季,小肠长和大肠长系数均无季节性差异。结果表明,随着季节更替,黑斑侧褶蛙消化道各段的重量和长度表现出一定的弹性特征,这与各器官的功能及其生活环境的多样性是相适应的。