Homo Sapiens: Anatomically Modern Humans (AMH)

new

Admin
Administrator

Posts: 81,611

Homo Sapiens: Anatomically Modern Humans (AMH) Dec 16, 2019 18:36:06 GMT

Quote

Post by Admin on Dec 16, 2019 18:36:06 GMT

VOWEL QUALITIES CAN CONTRAST WITHOUT A LOW LARYNX: FUNDAMENTALS OF SPEECH ACOUSTICS
In a recent handbook on animal bioacoustics, Fitch and Suthers (93) discuss the difficulties biologists encounter trying to adapt the principles and methods of speech research to study animal communication. As an advanced introduction to the topic and to subsequent discussion, we aim in this section to present certain fundamentals of speech production, VT modeling from birth to adulthood, and vowel system organization that we have found crucial for the analysis of primate vocalizations. Many of these ideas are detailed further in classic textbooks [e.g., (94, 95)].

Let us note that the material we present consists also of concepts and methods developed over more than two decades of work by multiple overlapping international multidisciplinary teams (including researchers in phonetics and vowel universals, VT modeling, acoustic speech processing, anatomy, genetics, VT ontogeny, speech development, paleo- and physical anthropology, primatology, and cognition), linking a core group at GIPSA-lab in Grenoble, France, with researchers from many different laboratories. This multidisciplinary collaboration was necessary to reopen the doors to lines of inquiry and research on the emergence of speech that had been effectively barred by the consensus around LDT.

Source-filter theory
The acoustic spectrum and formant structure of the speech signal were made visible by the spectrograph (96) and then readable by the acoustic theory of speech production (97), the two combining to reveal the relationship between formants and certain key aspects of the VT configurations. This section explains the core of that theory and its instantiation in modern articulatory-acoustic research on speech.

Principles. Fant’s acoustic theory of speech production (97) is also known as the source-filter theory because it explains speech sounds as arising from glottal vibration as a source signal, which is then modified by the VT as a filter (with the simplifying assumption that minor interactions between the glottal source and the VT are discounted). The speech signal in typical vowels (i.e., voiced oral vowels) comes from the expiratory airflow that initiates or maintains periodic modulation by the aerodynamic effects of its passage through the glottis (the gap between the vocal folds). That source signal is a plane wave that moves from the glottis, through the VT, and out at the lips. It is spectrally simple, with the energy decreasing rapidly up the F0’s harmonics (successive multiples of F0, the vocal folds’ frequency of vibration). The VT transforms the acoustic spectrum supplied by the laryngeal source and redistributes its spectral energy by filtering it according to the resonance characteristics implied by the VT’s configuration.

Acoustic theory allows determination of the VT’s filter characteristics through several analytical steps. First, because the VT is a bent nonuniform tube, the VTL must be evaluated in 2D along the VT’s median line in the midsagittal plane, from the glottis to the lips. MRI [e.g. (98)] has replaced lateral radiography and tomography [e.g., (97)] for this step. Then, the transverse cross-sectional area, the third dimension of the VT, is sampled in planes perpendicular to and along that median line. These sampled areas are reconstituted as “stacked” cylinders aligned axially on their centers, resulting in a straight tube with variable sections [the acoustic effects of straightening are negligible; (99)], which is acoustically equivalent to the VT. Plotting those areas gives the area function, specifying the cross-sectional area of each cylindrical element as a function of its distance from the glottis.

Fig. 1 Source-filter theory.
Interpreting vowel spectra as the result of the transformation, by the VT, of the glottal source . (A) Source. Top: view from above on the vocal folds; bottom: spectrum of the glottal source signal, with high amplitude in low frequencies. (B) Filter. Top: sagittal section of the VT, with the median line (dotted) where VTL is calculated; middle: VT’s area function; bottom: VT’s acoustic transfer function; black: calculated from the area function; red: extracted by LPC analysis from speech signal. (C) Radiated sound. Top: classic spectrogram of a synthesized vowel, showing formants and their peak frequencies over time [here calculated by Praat (171)]; bottom: vowel’s acoustic spectrum, whose amplitude envelope (dotted line) is imposed on the source signal by the VT transfer function.

From that area function—which is an acoustically sufficient 3D representation of the VT—Fant’s theory enables calculation of the acoustic transfer function, which quantifies the filter that the VT applies to the glottal source. The amplified regions in the resulting spectrum are termed formants, labeled Fn and numbered from low to high frequencies (F1 the lowest, F2 next, etc.). They are the key to contrasting vowel qualities in human speech (specifically, the first three formants, F1-F3, characterize the contrasting vowels of human speech, acoustically for researchers and perceptually for listeners). Formants can also be calculated indirectly from a recorded speech signal, either by visual analysis of a classic spectrogram or through digital processing using fast Fourier transform or, as we discuss below, LPC analysis. The analytical keys to the source-filter theory are illustrated in Fig. 1 (presented right to left, in keeping with the century-plus convention in phonetics of presenting the sagittal section from its left, a convention we follow throughout this paper).

Source-filter theory has been widely adopted for research on mammal vocalizations and, more generally, for bioacoustics (40, 93, 100, 101). Because the spectral energy in human speech rolls off sharply as frequency rises (as noted above), detection of F4 is uncertain and that of higher formants is rare. In other primates, though, researchers typically detect F6 (43) and higher, sometimes up to F12 (102). This is possible because the glottal source signal in primate vocalization is regularly very rich up to the high spectral frequencies.

Formant extraction by LPC. LPC was developed in the late 1960s [see (37) for historical perspectives] and became common in speech research during the 1970s to allow estimation of the VT transfer function directly from the speech signal. While the mathematical details and LPC’s specific strengths, difficulties, and limits are beyond our scope here [see (103, 104), or (105) for different treatments of those aspects], LPC exploits the redundancy in the signal by using a sequence of samples of the digitized signal to predict the subsequent samples. This method has the advantage of separately calculating the rapid changes attributable to the laryngeal source from the slower changes in resonance patterns (i.e., formants) due to movement of the VT. This makes it essentially parallel to the source-filter theory (97) in separating the effects of the glottal source from the VT as a resonating filter and gives it its power as a tool to isolate and specify formant values. Note, however, that to use LPC successfully, the user must specify the number of formants expected in the signal. Years of experience with LPC have taught researchers to manage these settings for the different talkers and various vowels of human speech, but the settings are difficult to determine for primate vocalizations, and we are just beginning the long effort to master them (35). It is perhaps for this reason that, as we will see later, animal communication research did not incorporate LPC analysis until the late 1980s, about two decades after its appearance in speech research.

Admin
Administrator

Posts: 81,611

Homo Sapiens: Anatomically Modern Humans (AMH) Dec 16, 2019 22:35:27 GMT

Quote

Post by Admin on Dec 16, 2019 22:35:27 GMT

Relating VT shapes to acoustic resonances
Tubes, cavities, constrictions, and acoustic resonances. VT shapes are spectrally characterized by their acoustic resonances (formants) so that every variation in VT configuration produces variations in the spectrum and in the resulting formant pattern. Contrary to Lieberman’s reasoning in his founding papers, the set of formants achievable by a given acoustic tube does not depend directly on the anatomical structures defining its shape (i.e., the oral and pharyngeal cavities) but mainly on its length and the arrangement of acoustic “cavities” and “constrictions” along that length, as will be discussed now.

As a principle, speech science has known at least since Fant (97) that production of vowels requires control of the area of the lip opening (Al) and of both the location (Xc) and area (Ac) of a VT constriction—that is, a place in the VT where the narrowing by the tongue toward the palate, velum, or pharyngeal wall defines relatively decoupled acoustic cavities. In the phonetic tradition, the two parameters Xc and Ac define the height and place of articulation of the vowel, and the parameter Al is a correlate of rounding or labialization. Examining these aspects of the three extreme vowels, the observed shapes are /i/ with a large back cavity, a long narrow constriction by the tongue dorsum in the front of the palate, and a small flared opening at the lips (Fig. 2A, top); /a/ with a short constriction low in the pharynx followed by a flared bell shape (Fig. 2B, top); and /u/ with two large closed cavities of roughly equal size, the back one closed by the tongue dorsum around the midpalate and the front one closed at the lips by protrusion with very tight rounding (Fig. 2C, top). Note also that the sensitivity of the three parameters differs across vowels: For /i/, Al can vary as long as the lips are somewhat open, whereas Xc, the constriction location, must be very precise; for /a/, Al is similarly variable, but the ratio of Al/Ac is important for F1 (106); and for /u/, both the lip opening and the constriction must be very small, while the constriction location can vary through the middle of the VT (107, 108). In LDT’s founding publications, Lieberman’s VT simulations (9, 10) apparently did not attain the small, accurate constrictions necessary in the high sensitivity areas of /i u/ or the Al/Ac ratio for /a/.

Fig. 2 Production of the three extreme vowels /i/, /a/, and /u/.
(Top) Sagittal section (with the median line along which the VTL is measured from glottis to lips) with dots indicating the lips (location of Al) and the vowel’s constriction (with location Xc and area Ac) along the VT. (Middle) Area function, with dots in corresponding locations. (Bottom) Acoustic transfer function, with the lowest formant peaks marked (F1 to F4).

The classic four-tube model of Fant (97) used the component tubes to represent not the anatomical cavities per se (pharynx and oral cavity) but the acoustic cavities characterized by the tongue constriction and the lip opening. In his representation, the tubes representing the lip opening and the constriction are of fixed length, with variable areas representing Al and Ac. The constriction scrolls through the model as a whole, so the model does allow both a constriction at the lips and an internal constriction whose placement is flexible and can be directed from /a/, through /u/, to /i/. It thus instantiates the control parameters of Fant’s source-filter theory, as Fant demonstrates with spectra and F1-F5 frequencies for a range of (Xc, Ac, Al) values.

Crucially, the acoustic cavities do not correspond directly to the oral and pharyngeal anatomical cavities, nor is there any need or use for a 1:1 SVTh/SVTv relationship. Instead, the acoustic cavities are defined by jaw opening, tongue shape, and the lip pavilion shape. This erroneous presupposition of equivalence between anatomic (oral and pharyngeal) and acoustic (front and back) cavities is the core flaw of LDT and can be traced to its founding publications.

Maximal acoustic space. Our team contributed an important methodological advance by formalizing the idea of the “maximal acoustic space” (MAS) of a given tube model. The MAS consists of the exhaustive exploration of the range of (F1, F2)—and possibly (F1, F2, F3)—values attainable by the model. For this purpose, we used an n-tube model (29) incorporating, but more general than, the four-tube model introduced by Fant (97) and determined the MAS in the following way. We set a fixed overall model length l (e.g., the 17.5 cm typical of the VT of an adult male human) and a plausible Ac range for vowel production (i.e., a minimum large enough to avoid consonantal turbulence effects and a maximum small enough to be articulatorily realistic). We divided the tube into the required n component tubes, set areas for each component tube, and calculated the acoustic transfer function to extract F1 and F2 values. Each such model will have n − 1 degrees of freedom for the locations of the tube’s divisions and n degrees of freedom for the areas the tube, for a total of 2n − 1 degrees of freedom. Applying a Monte Carlo method, we randomly generated a large number of values for these variables (typically 500,000 sets, for high precision along borders) and thus determined the full extent of the F1-F2 space available to the model specified, i.e., a model of that length with that number of component tubes.

With this technique, we showed that all n-tube models when n ≥ 4 cover the same area in the F1-F2 space and hence correspond to the same MAS. We also showed that the set of possible (F1, F2) values corresponds to the classical vowel triangle with the uniform tube at the center and /i a u/ at the corners. This shows that it suffices to be able to produce a constriction anywhere inside the tube plus one at the labial end to ensure that the whole set of (F1, F2) values is reachable inside the vowel triangle. This confirms that anatomical details per se—such as the length of the pharyngeal region and the resulting SVTh/SVTv ratio—do not restrict the articulation of any vocalizations inside the vowel triangle: For a given VTL, it suffices to exhaustively vary the three parameters (Xc, Ac, and Al).

These results corroborate Fant’s choice of the four-tube model. Our equivalent model (with n = 4) gives schematized area functions that illuminate the relationships between the cavities and the formants (see Fig. 3). VT configurations characteristic of the three corners of the MAS show that there is no configuration capable of making these point vowels other than those mentioned previously: for /a/, a discretized horn shape with tube of increasing areas; for /i/, a small open front cavity and a large closed back cavity configured as a Helmholtz resonator (see Fig. 3 for explanation), where the palatal constriction serves as its neck; and for /u/, two closed cavities as Helmholtz resonators with the necks (the constrictions) enclosing approximately equivalent volumes by positioning the tongue near the uvula and closing the lips. The uniform tube corresponds to the schwa, /ə/, around the center of the F1-F2 vowel triangle. Crucially, all vowels of the world’s languages can be displayed and positioned precisely inside the MAS, as shown in Fig. 3.

Fig. 3 Four-tube MAS, main IPA vowels, and schematic /i a u/ configurations.
The MAS was set at l = 17.5 cm. In the vowel configuration schemas, the dots show the key points of the VT constriction (for Xc and Ac) and the lip opening (Al). A Helmholtz resonator consists of a body of volume V that is extended by a neck of length L and of area A. Because the frequency of a Helmholtz resonator is proportional to A/(LV)−−−−−−√, the smaller and longer the neck, and/or the larger the volume, the lower the resonance. The single Helmholtz resonator of /i/ gives it its low F1, and the pair of Helmholtz resonators in /u/ make both F1 and F2 low. Note that the orientation of the F1 and F2 axes in the MAS is standard in speech research to match the preexisting conventional orientation of the vowel triangle in the IPA, defined by tongue position of a speaker facing left. Note also the color scheme of the IPA vowels, which is used here and below for convenience.

The finding that the MAS forms a triangle with /i a u/ at the extrema constitutes evidence that it is not, as LDT claimed, a particular anatomical configuration (specifically, a lowered larynx enlarging the pharynx or a 1:1 SVTh/SVTv ratio) that permits articulation of these three vowels, which are nearly universal in human languages. Rather, the intrinsic properties of tube acoustics are exploited via talkers’ articulatory control to generate the acoustic triangle and thus furnish the maximum potential for vowel differentiation. That is, knowing only a VT’s length (and nothing about its anatomy), one can calculate its MAS, locate a given production therein, and determine its phonetic value and its symbol in the IPA. With appropriately sampled vocalizations (e.g., from a given species), such analysis can show whether the vocalizations cover the MAS and exploit its full potential for contrast. The MAS can thus serve (as we will see below for nonhuman primates) to compare vocalic qualities produced by VTs of differing lengths. For instance, using the data from Peterson and Barney (12) (data publicly available in Praat), we observe that the dispersion ellipses for American English vowels uttered by men, women, and children are well dispersed and cover their representative MASs reasonably well for VTLs of 17, 15, and 12.5 cm, respectively (Fig. 4).

Fig. 4 American English vowels displayed within the MASs calculated by the four-tube model.
Dispersion ellipses are for standard vowel values from Peterson and Barney (12) for young speakers, adult females, and adult males, displayed in a MAS for the appropriate VTL, 12.5, 15, and 17.5 cm, respectively.

Despite its simplicity (for instance, its lack of distinction of SVTh and SVTv), the MAS generates the entire F1-F2 vowel space possible for a VT of a given fixed length. However, because it also generates forms impossible for the tongue to articulate, it does not allow “inversion” from acoustic (F1, F2) values to retrieve exclusively realistic articulations, as when analyzing recorded vocalizations. To do so, we introduce in the next section a different kind of model incorporating anthropomorphic constraints.

Anthropomorphic articulatory modeling
Expanding on the work of Lindblom and Sundberg (109) and Harshman et al. (110), Maeda (111) improved the articulatory modeling of the VT using a principal components analysis of the variability of a number (typically 30) of sagittal sections (Fig. 5A) typically obtained by cineradiography (112) of a native talker pronouncing a representative French corpus. (Note that French includes the three extreme vowels, /i a u/, that are reference points for the IPA.) His analysis reduced the partially correlated sagittal view contour points to a set of linearly uncorrelated control parameters closely related to known articulatory variables (e.g., jaw, lips, tongue, and larynx), which then drive the model as command parameters controlling, e.g., vertical larynx position, tongue position, jaw position, and lip opening. For Maeda’s model, the seven control parameters account for 70 to 90% of the observed variation in vowel productions (Fig. 5B) (111, 113).

Fig. 5 Anthropomorphic articulatory model.
(A) Measurement of the VT in the sagittal section with an analysis grid to sample the VT area in (typically) 30 planes transecting the VT. (B) Articulatory command parameters extracted using a principal components analysis of the sagittal section data. These parameters are interpretable with regard to the articulators: for the lips, (1) opening height and (2) protrusion; for the jaw, (3) the opening; for the tongue, the movements of (4) the dorsum, (5) the body, and (6) the apex; and for the larynx, (7) its height.

This model naturally suggests a mapping between the model’s control parameters and the in vivo articulators, which was later investigated for tongue muscle activity through electromyography by Maeda and Honda (114). Confirmation comes from further studies both by electromyography (115, 116) and biomechanics (117), which also showed that there existed a simple mapping between activity of the tongue muscles (hyoglossus, anterior and posterior genioglossus, and styloglossus), the tongue parameters of the model, and the F1-F2 pattern.

The anthropomorphism of Maeda’s model allowed it to generate the F1-F2 maximum vowel space (MVS) (118, 119). The MVS’s range is explored by applying the Monte Carlo method to the seven control parameters (similar to our development of the MAS, discussed above) and then synthesizing and plotting the resulting vowels. The evident similarity of the MVS and the MAS (see Fig. 6 and “Tubes, cavities, constrictions, and acoustic resonances” section) shows that the anatomically realistic VT of Maeda’s model and in vivo VTs of live humans have the same acoustic potential as the n-tube models used to develop the MAS, and both the MAS and the MVS can generate the full F1-F2 vowel space. Furthermore, Fig. 6 also shows that the MVS is compatible with formant values obtained from a large set of human vocalizations for adult male speakers of eleven languages: Chinese, Dutch, American English, French, German, Japanese, Indian Malay, Brazilian and European Portuguese, Sardinian, and Swedish. However, crucially, Maeda’s model generates only anatomically realistic articulations. In a sense, it filters out the unrealistic articulations allowed within the MAS, and it has therefore been used, as n-tube models cannot, for inversion, to derive accurate articulatory configurations from vowels recorded in vivo (see Fig. 6, bottom).

Fig. 6 MVS for the anthropomorphic articulatory model.
(Top) Vowels of 11 world languages are projected into the maximal vowel space: Chinese (172), Dutch (173), American English (12, 87, 174), French (175, 176), German (177), Japanese (178), Indian Malay (179), Brazilian and European Portuguese (180), Sardinian (181), and Swedish (182, 183). Vowel labels from the original publications are coded according to the colors in Fig. 3. In addition, the low vowels, /æ a ɑ ɒ/, are grouped in a single macro-class. This F1-F2 space was generated by Maeda’s model, and the model is validated by the correct placement of the different languages’ vowels inside the MVS. (Bottom) Fifty sagittal sections (second row) and 50 area functions (third row) for /i a u/ (left to right) were obtained by acoustic-to-articulatory inversion from (F1, F2) values from French. Both are variations around those presented in Fig. 2, with dots in the sagittal sections and the area functions showing the positions of the labial and lingual constrictions, which thus allows computation of mean values for the crucial variables Xc, Ac, and Al. They illustrate, here for an adult male, prototypical VT forms, as well as the differing sensitivities noted in the “Tubes, cavities, constrictions, and acoustic resonances” section for lip area, Al, and tongue constriction position and area, Xc, and Ac. With this method, one can use formant values to generate plausible sagittal sections for all the vowels of the IPA.

VT growth and acoustic normalization
The anthropomorphic model introduced above (111) deals with adult anatomy and articulation, but VT growth is, of course, crucial for LDT. A number of studies have been done in this domain and led to modifications of the articulatory model for dealing with the VT shape and size variations associated with ontogeny.

VT morphology depends on the bony structures of the head and cervical vertebrae. These situate and anchor the jaw, teeth, and hard palate, beyond which the tract is bounded by soft structures (tongue, pharyngeal walls, velum, and lips) with insertions into those bony structures. Over the course of ontogeny, the shape of the VT will therefore depend crucially on the growth of the skull and cervical vertebrae and on the positioning of the hyoid bone from which the larynx hangs. While modeling had previously been based principally on radiography of adult VTs, Goldstein (26) took on the task of integrating a wide array of anatomical data into an articulatory model of VT growth. From a database she assembled from data on the bony anatomy in published medical literature based on radiography of the head and neck, she selected 19 measurements (16 distances and 3 angles) showing the changes in VT morphology from birth to adulthood for both sexes. In particular, her data integrate the uneven growth rates of the two key LDT parameters determining the VTL: the SVTh increase is small and slow while the SVTv increase is large and rapid (Fig. 7, B and C). All these data were fitted to age with simple or double logistic functions, which have been extensively studied and applied to a wide range of biological systems.

Fig. 7 Human VT growth.
(A) Schematic VT illustrating the three pertinent measures: SVTh and SVTv, and the dashed median line where VTL is measured. (B to D) SVTh (B), SVTv (C), and VTL (D), from around birth to 25 years, females in red and males in blue. Results from Barbier et al. (123, 124), as measured from four longitudinal databases, from 1 month to adulthood, using images from the American Association of Orthodontists (68 subjects, 966 x-rays), plus 12 fetal images from Montpellier University are shown. The data are optimized by two double logistic functions to account for growth in two phases, from birth to puberty and then from puberty to adulthood (26, 184). Radiography did not capture the male glottis beyond 15 years, so the function in that range (dotted line) is an estimate. (E) VTs generated by VLAM (cf. VT growth and acoustic normalization section), from a human newborn through an adult male, along with their corresponding MVSs, with the three point vowels /i a u/, plus schwa /Ə/. (F) Color-keyed boundaries of the five MVSs from (E) normalized to 17.5 cm, the mean length for a male at 25 years, with the /i a u/ vowels normalized from: predictions from Goldstein’s model (26) for newborns.

Admin
Administrator

Posts: 81,611

Homo Sapiens: Anatomically Modern Humans (AMH) Dec 16, 2019 22:37:13 GMT

Quote

Post by Admin on Dec 16, 2019 22:37:13 GMT

Acoustics of the uniform tube
Uniform tube: The ultimate simplification of VT models. The uniform tube is a key element for analyzing vocalizations in LDT (Fig. 8). A VT has variations of form along its length but can be configured in speech to maintain a generally uniform cross-sectional area from one end to the other, from the glottis to the lips. The uniform area allows it to be modeled by an acoustically equivalent cylindrical tube of the same length, closed at one end (the glottis) and open at the other (the lips). This is termed a quarter-wave resonator. The characteristics of such a model include that the formants are evenly spaced throughout the spectrum. Like all formants, their frequencies are proportional to the length of the tube, while the even spacing is diagnostic of a tube’s uniformity. For our purpose, this means that for primates vocalizing through a uniform tube, those with long VTs will have formants evenly and closely spaced, while those with short VTs will have them evenly and distantly spaced. A further notable characteristic of uniform tubes closed at one end and open at the other is that the frequencies of higher formants are odd multiples of F1 (F2 = 3F1, F3 = 5F1, …) (Fig. 8).

Fig. 8 Spectral properties of uniform tubes.
(A) Acoustic transfer function of a uniform tube where l = 17.5 cm. Its calculation incorporates effects (lip radiation, wall losses, and viscosity) that slightly modify the theoretical formant values (0.5, 1.5, 2.5 kHz, …) (97, 185). The human VT configured as a uniform tube produces the schwa vowel, /Ə/. (B) Wave patterns in the uniform tube. The uniform tube models the VT as a quarter-wave resonator closed at the glottis and open at the lips, so tube acoustics generate formant values at frequencies defined by the odd multiples (1, 3, 5, 7, …) of one quarter of a wavelength, λ, equal to four times the length of the tube. The top of this panel shows the volume velocity wave along the tube for all of the first three formants. Below are the individual wave shapes for each of the first three formants, plotted individually (14). (C) Formant values for pertinent lengths of uniform tubes. This graph shows the formant values for uniform tubes with lengths across a range of VTLs, calculated (in kHz) as Fi = 35(2i − 1)/4ℓ, with lines marked at VTL values known for selected species noted in this paper. These are the formant values that should be expected when a VT of that length is configured as a uniform tube.

Formant pattern of the uniform tube as a test. Riede et al. (88) were the first to test animal vocalizations (namely, Diana monkey alarm calls) for compatibility with uniform tube characteristics, specifically with F2 = 3F1. They used a speech science approach to situate the calls by their formant patterns relative to human vowels produced by children with a similar VTL [as documented by (87)]. Riede and colleagues projected the formants into F1-F2 space to see whether they fell along the F2 = 3F1 line (Fig. 9). They showed that Diana monkey eagle alarm and leopard alarm calls are not schwa-like but are similar to /a/ as pronounced by 10- to 12-year-old children.

Fig. 9 F1-F2 MAS plane for men; dispersion ellipses for /u/, /æ/; and the straight line F2 = 3F1 produced by a uniform tube varying across VTL values.
MAS set to VTL = 17.5 cm, data from Peterson and Barney (12). Points and means correspond to the values for adult males of the formants of /u/ and /æ/ and to the schwa-like /Ə/. This shows that unless the VTL is known, the F2 = 3F1 criterion is insufficient for detecting the schwa-like productions of a uniform tube.

Note that the (F2 = 3F1) criterion is deceptive, as it underdetects certain nonuniform VT configurations as uniform. The F2 = 3F1 line crosses the entire vowel triangle and thus necessarily crosses a limited but important selection of nonuniform vowel configurations, from /u/ at one extreme to /æ/ at the other. Because the formants of baboon grunts fall along that line, but in the /u/ area, it is not surprising that they were mistakenly ascribed to production by a uniform tube [e.g., (42, 44)]. Ultimately, the F2 = 3F1 criterion is necessary, but not sufficient, to detect a uniform tube. Information about the VTL is also needed to normalize formant values and locate them in an MVS relative to IPA vowels.

VTL estimation from formant patterns
As noted above, an estimate of VTL is crucial to represent vocalizations in an F1-F2 acoustic space and label them relative to IPA vowels. Because the formants of a uniform tube are evenly spaced through the frequency spectrum, the VTL can be found directly from any given formant (Fi), using
ℓ=(2i−1)c/4Fi
where c is 350 m/s, the speed of sound in humid VT air at 35°C (approximating primate body—and VT—temperature). We therefore propose that all VTL estimates from all formants using this method should agree for the tube to be recognized as uniform with the same resulting l. Otherwise, the tube is nonuniform, and some other method must be found to estimate the VTL.

Using this test, we have detected various important discrepancies, for instance, regarding baboon grunts observed by Rendall and colleagues (71). In a uniform tube, the estimations using the first four formants (F1, …, F4) measured in males would imply VTLs ranging from 23.3 to 32.6 cm and 16.3 to 22.9 cm for females. These are seriously disparate VTL values and entirely implausible for baboons, where we have measured VTLs of 13.5 cm for males and 11 cm for females (35). Similarly, Owren and colleagues found means of VTLs estimated from the first four formants (F1, …, F4) varying from 15.9 to 19.7 cm. These discrepancies intrigued the researchers, who noted:

[T]he derived lengths were significantly longer and shorter, respectively, than expected (based on the mean overall estimate [17.9 cm]). (44)

Note that in these examples, the VTL is frequently overestimated, as it would be in human speech if calculated from the first formants of /u/. For instance, the F1 and F2 means found by Peterson and Barney for American English /u/ in adult males would, respectively, imply VTLs of 29.2 and 30.3 cm, too long—absurdly so—for a VTL often cited at 17.5 cm, but analyzed as 19.6 cm for /u/ (140). The pertinent vocalizations, baboon grunts, do show /u/-like formant patterns, as we will show below.

An estimate based on a single formant is necessarily imprecise, considering the intrinsic uncertainty associated with formant estimation. Hence, various methods have been proposed capitalizing on the previous equation but adding statistical tools to make the evaluation more robust.

One method that has been proposed is
ℓ=c/2Df
where Df is the mean of several successive intervals from F1 to Fn (43), which reduces to
Df=(Fn–F1)/(n–1)

A second, more sophisticated and precise tool uses the slope Df of the linear regression between the formant numbers (1, 2, 3 … n) and their respective values to estimate formant spacing (141).

With n > 4, these two propositions have the advantage of minimizing the importance of F1 and F2, the formants most influenced by VT deviations from a uniform tube configuration, and they tend to show that higher formants give good VTL estimates even for nonuniform VTs. Expressed differently, the frequencies of higher formants, regardless of the VT’s shape, tend to converge on those of a uniform tube. If the higher formants are detectable, as is often the case with primate vocalizations, these two methods are effective for estimating VTL, even in the case of nonuniform tube configurations. In the following sections, we have relied on the second method as potentially more robust.

LDT falsified in nonhuman primates
With this battery of principles and tools, we can now address the existing acoustic data on primate vocalizations, and we can plan and execute targeted experiments and discuss their implications for the LDT.

Discrepancies detected. A number of papers in the past 15 years have led their authors to raise doubts that their acoustic measurements of nonhuman primate vocalizations were compatible with the even formant spacing expected from a uniform tube. The literature contains numerous remarks by primatologists confronted by formant patterns unexplained by LDT, such as:

For many years, it has been the default assumption that mammalian vocal tracts, including those of non-human primates, resemble a uniform or flared tube during vocalization (Lieberman, 1968; Lieberman et al., 1969; Shipley et al., 1991). In a uniform cylindrical vocal tract the resonance frequencies are expected to appear as odd numbered multiples of the first resonance, and all resonances are evenly spaced. … More recently, various studies challenged this view, by suggesting that some animal vocalisations are the product of non-uniform vocal tracts (e.g., Owren et al., 1997). For example, we have previously demonstrated that the location of the first (F1) and second (F2) formant in Diana monkey alarm calls cannot be explained by a uniform vocal tract but must be the result of a more complex vocal tract geometry. (88)

We show in Fig. 10 a selection of spectrograms with distinctly irregular formant spacing, which thus indicate a departure from the schwa-like acoustics resulting from a VT shaped like a uniform tube. Figure 10 (C and D) also shows modification of the VT configuration over the course of the vocalization. Riede et al. (88) suggest that “the acoustic structure of these calls is the product of a non-uniform vocal tract capable of some degree of articulation”. Pisanski and colleagues (5) “suggest that this may represent a living relic of early vocal control abilities that led to articulated human speech”.

Fig. 10 Formant patterns of vocalizations (red lines) diverging from those of uniform tube (green lines).
The green lines represent calculated estimates of the expected formants from a uniform tube of the appropriate VTL, while the red lines represent either values reported by the authors or means calculated from their figures, adapted here for graphic purposes. VTLs for (A) to (C) were estimated with the Reby and McComb method using five formants for (A) and (B) and six for (C). VTL for (D) was measured from x-rays. (A) Double grunt of Gorilla gorilla beringei [Fig. 1 of (41)]; VTL = 16.4 cm. F1 is much too low for a uniform tube. (B) Grunt of Papio hamadryas adult female [Fig. 2 of (102)]; VTL = 17.3 cm. F2 is much too low for a uniform tube. (C) Roar of Eulemur mongoz [Fig. 1A of (186)] with initial formant transition; VTL = 10.7 cm. Final formant values are compatible with a uniform tube, but the variations of F2, F3, and F4, while F1 stays stable, are not compatible with a uniform tube. (D) Leopard alarm call of male Diana monkey [Fig. 2 of (88)]; VTL = 10 cm. As noted by the authors themselves, neither the F2 values nor the (F1, F2) variations along the trajectory are compatible with a uniform tube.

Two focused experiments, two explicit refutations. Two articles appearing 3 weeks apart (35, 142) ultimately proved the LDT untenable. In the first article, Fitch et al. showed that the macaque VT attained articulatory configurations distinctly different from a uniform tube during vocalization and also during feeding and facial expressions. The authors conclude:

We demonstrate that the macaque vocal tract could easily produce an adequate range of speech sounds to support spoken language, showing that previous techniques [Lieberman, Klatt, Wilson, 1969] based on postmortem samples drastically underestimated primate vocal capabilities. Our findings imply that the evolution of human speech capabilities required neural changes rather than modifications of vocal anatomy. Macaques have a speech-ready vocal tract but lack a speech-ready brain to control it. (142)

One of the authors later states that:

Now nobody can say that it’s something about the vocal anatomy that keeps monkeys from being able to speak. [Ghazanfar in (143)]

After years of sometimes harsh debate, during which they essentially reversed their position (138, 144, 145), they finally converge on what they term the neural hypothesis, a conclusion advanced by Boë over a decade earlier based on simulations of a VT with a small pharynx:

Endowed with a small pharyngeal cavity, monkeys exhibit the same vocal tract configuration as newly-born infants, but if they do not produce vowels, it is not due to this resemblance. ... No, if monkeys do not talk, according to present evidence, this is due to a lack of appropriate cortical equipment. (27)

For their part, Boë and colleagues show (35) that baboons [Papio papio (146)] naturally produce vowel-like sounds sharing the (F1, F2) formant structure of the human [ɨ æ ɑ ɔ u] vowels, including the proto-bisyllabic call wahoo, and that those vocalic qualities are organized in a proto-system similar to that of humans:

Our findings therefore reveal a loose parallel between human vowels and baboon VLSs [Vowel Like Segments] by demonstrating that both have a phonetic inventory of vocalic qualities differentiated by formant structure and that these structures are characteristic properties of vocalizations produced in distinct social contexts or for different functions. From an evolutionary standpoint, demonstration of a two [articulatory] axis vocalic proto-system in baboons suggests that the human vocalic system did not emerge de novo but originates from articulatory capacities already present in our common ancestors. (35)

After earlier challenges to LDT for children and Neanderthals, these two articles bring the challenge to the realm of nonhuman primates using two complementary approaches. Fitch and colleagues used medical imagery techniques to directly determine VTL and VT configurations, then articulatory-acoustic modeling to estimate the formants for a male rhesus macaque, and finally generated an example of hypothetical macaque articulatory capacities by dynamic synthesis of a whispered sentence. Boë and colleagues submitted more than a thousand naturally produced baboon vocalizations [recorded and ethologically documented from a research baboon troop in semi-liberty (59)] to LPC analysis for measurement and assignment to five phonetic categories corresponding to five ethological situations. They added an anatomical study to measure the VTL and document the tongue musculature recruited to produce the vocalizations. With the VTL normalized and a corresponding MAS generated, the superimposition of the Peterson and Barney vowels allowed them to categorize the baboon vocalizations as using five separate proto-vowels. In Fig. 11, we present a MAS with dispersion ellipses for selected Peterson and Barney vowels (from child talkers) for comparison with (i) the macaque findings of Lieberman et al. (10) and Fitch et al. (142) and (ii) our own 2017 findings concerning baboons. Unlike Lieberman et al., both Fitch et al. and Boë et al. found articulations well beyond the schwa-like uniform tube configuration.

Fig. 11 Phonetic qualities of macaque and baboon articulations within the MAS.
(Left) Macaque vowel spaces, according to Lieberman et al. (10) (white line) and according to Fitch et al. (142) with the convex hull (black line) enclosing data from vocalizations, facial expressions, and eating. (Right) Vocalizations from Boë et al. (35) with the convex hull (black line) enclosing data from vocalizations. For both sides, all the data were either obtained from or normalized to a reference VT of 11.4 cm [the VTL of the macaque in (142)] and presented along with the dispersion ellipses (color-coded as in Fig. 3) for Peterson and Barney’s data for children (12), also normalized to a VTL of 11.4 cm.

Note the enlargement of the acoustic space found for vocalizations over the three studies, which may be explicable by the different conditions of data collection for each study. Lieberman and colleagues used molds of a postmortem VT, which fixes the articulatory configuration and makes it difficult to challenge any extrapolations from the VT’s form. Fitch et al. used x-ray video of live animals, but any radioimaging setup is necessarily constraining, and both the surroundings and the absence of companion troop members must leave the subject in an ethologically unnatural situation. The vocalizations used in the Boë et al. study were produced spontaneously by a troop of baboons living mainly outdoors in semi-liberty under near-natural conditions. Apparently, the more natural the data collected, the larger the acoustic space covered.

These two studies are functional replications of foundational LDT studies, Fitch et al. of (10) and Boë et al. of (8). Their findings constitute strong and probably definitive arguments for the refutation of the LDT.

Last Edit: Dec 16, 2019 23:14:15 GMT by Admin

Admin
Administrator

Posts: 81,611

Homo Sapiens: Anatomically Modern Humans (AMH) Dec 17, 2019 18:23:58 GMT

Quote

Post by Admin on Dec 17, 2019 18:23:58 GMT

Diamonds in the coal: New findings from vintage data
From pertinent publications, we have selected data regarding various nonhuman primate vocalizations showing irregularly spaced formant patterns impossible to produce with the uniform VT corresponding to schwa. We noted the published formant values and determined the associated VTLs, either measured by the authors using radiography or MRI or estimated by us from those measured formants using Reby and McComb’s procedure (141). We then generated adjusted formant values, through normalization to a standard VT with a VTL of 11.4 cm, using our previously elaborated procedure (see 3.4.2 above). In Fig. 12, we have projected the normalized formant data into the corresponding F1-F2 space of the MAS, along with dispersion ellipses for selected vowels from Peterson and Barney’s data for children’s vowels (12).

Fig. 12 Reframing vintage data in the normalized MAS.

This figure collects and presents data from a variety of published articles on primate vocalizations. The MAS and all data are normalized to VTL = 11.4 cm [the VTL of the macaque in (142)]. Original (prenormalization) VTLs are determined using the articles’ formant values and Reby and McComb’s method (141) (discussed in the “VTL estimation from formant patterns” section) except VTLs for chacma baboon males: estimated from known VTLs of other baboon species; chacma baboon females: 25% shorter than males, because formants are 25% higher (187); and Diana monkeys: from radiography (88). Vowel dispersion ellipses for /i ɪ æ ɔ ʊ u/ are from Peterson and Barney’s data for children (12).

LESSONS LEARNED FROM THE LD CONTROVERSY
The LDT claimed that production of differentiated vowel qualities was anatomically impossible except in AMHS adults. Since its formulation and diffusion beginning in the 1970s, a hypothesis has arisen [e.g., see (3)] that the emergence of speech and language was recent, sudden, and simultaneous: recent because contrasting vowels (and hence phonology) only became possible in AMHS [whose emergence was recently pushed back from ~200 to ~300 ka ago; (148)]; sudden because 300 ka is extremely short on an evolutionary time scale; and simultaneous because both speech and language would need that short period to develop.

Three major facts emerge from our review of ground-truth data in light of articulatory-acoustic models and the use of the modern tools from speech. First, even among primates, LD is not uniquely human. Second, LD is not required to produce contrasting formant patterns in vocalizations. Third, nonhuman primates do produce vocalizations with contrasting formant patterns. Thus, the evidence is now overwhelming, from arguments based on both observations and modeling, that the LDT is no longer tenable. The larynx did descend in phylogeny (and still does in ontogeny), but the descent was neither necessary nor sufficient for the emergence of speech from primate vocalization. We find that the anatomical potential to produce and perceive sounds differentiated by their formants began at the latest by the time of our last common ancestor with Old World monkeys (Cercopithecoidea) about 27 Ma ago. That element of speech, at least, would have been available beginning then as the channel for communication by language during its emergence at any later time.

LDT was the most broadly disseminated and, to the best of our knowledge, the only broadly accepted claim to establish a time frame of the emergence of speech and language based on anatomical evidence. We have used the comparative method to show, using our own data and reanalyzed data from others, that a key element of human speech, contrasting vowel qualities, was available to our ancestor species at least 100 times earlier than previously theorized under LDT.

Of course, many other elements have been addressed in the lively discussions about the emergence of speech and spoken language, including such topics as cranial anatomy of premodern humans (149, 150), auditory sensitivity changes (151), risk of choking (152), laryngeal motor control (153, 154), and functional neuroanatomy (155, 156) [see a recent review of some of these topics in (157)]. The broader problem of the origin of language per se engages a further, more abstract set of topics, involving the biological, cognitive, and social conditions of language emergence [e.g., see the special issue introduced by (158)]. We intentionally declined to engage with these topics because, as we stated in Introduction, the ability to produce contrasting vowels is a foundational concern for the evolution of speech and spoken language, and ultimately of language in general, since the development of other aspects of speech (e.g., consonants, syllables, speech perception, and phonology), and thereby of a spoken lexicon available for syntactic manipulation, depends at a minimum on prior mastery of the articulatory ability to transmit those contrasting vowels. Our finding that that ability must have arisen so much earlier in the primate line casts a new light on several other lines of evidence and argumentation.

Specifically, the idea of recent, sudden, and simultaneous emerging of speech and language is no longer plausible. The dawn of speech in the form of contrasting vowel sounds is not recent, but early. The full process of speech emergence was therefore not sudden but extended, probably occurring in stages about which we can now begin to theorize. The final developments of this long process doubtless coincided with the emergence of language, but conceiving that much shorter process as simultaneous with speech emergence as a whole is no longer warranted.

Thus, we believe that the present refutation of the LDT should have a profound and liberating effect on our understanding of human evolution because, without the time limit imposed by LD, a variety of other hypotheses about language emergence can now be entertained. While speech had been thought of as enabling communication of already developed linguistic cognition, should it now be thought of as an early driver of linguistic cognitive development? For instance, gestural theories of language origin (33, 159) attracted increased support, in part, for allowing a longer window for language phylogeny from observed primate gesture, so should we suddenly abandon those theories and search for language phylogeny solely in observed calls, or should we investigate more broadly for communication by gesture and vocalization combined? In light of demonstrations that nonhuman primates can modify their VT shapes to differentiate vocalic qualities, should this be understood as exaptation of structures dedicated to breathing, chewing, and swallowing, and does this strengthen the “frame and content theory” argument (160, 161) that syllabic and phonological structure arose by exaptation of control of those same processes? The dawn of syntax had been sought in some triggering neurocognitive event (3, 162) contemporaneous with LD in AMHS, so should it now be imagined as a slower, more intricate exaptation of prior cognitive faculties common to primates? Other similar lines of reasoning, formerly understood as too “early” to apply to speech and language because they concern behavior of living primates, must also be reevaluated as possibly less premature: turn-taking (163, 164), laryngeal control (5, 165), audience effects (166, 167), and cultural transmission (168–170).

Science Advances 11 Dec 2019:
Vol. 5, no. 12, eaaw3916

Last Edit: Dec 17, 2019 18:25:25 GMT by Admin

Admin
Administrator

Posts: 81,611

Homo Sapiens: Anatomically Modern Humans (AMH) Apr 1, 2020 19:54:17 GMT

Quote

Post by Admin on Apr 1, 2020 19:54:17 GMT

Genetic information from an 800,000-year-old human fossil has been retrieved for the first time. The results from the University of Copenhagen shed light on one of the branching points in the human family tree, reaching much further back in time than previously possible.

An important advancement in human evolution studies has been achieved after scientists retrieved the oldest human genetic data set from an 800,000-year-old tooth belonging to the hominin species Homo antecessor.

The findings by scientists from the University of Copenhagen (Denmark), in collaboration with colleagues from the CENIEH (National Research Center on Human Evolution) in Burgos, Spain, and other institutions, are published April 1st in Nature.

"Ancient protein analysis provides evidence for a close relationship between Homo antecessor, us (Homo sapiens), Neanderthals, and Denisovans. Our results support the idea that Homo antecessor was a sister group to the group containing Homo sapiens, Neanderthals, and Denisovans," says Frido Welker, Postdoctoral Research Fellow at the Globe Institute, University of Copenhagen, and first author on the paper.

Reconstructing the human family tree

By using a technique called mass spectrometry, researchers sequenced ancient proteins from dental enamel, and confidently determined the position of Homo antecessor in the human family tree.

The new molecular method, palaeoproteomics, developed by researchers at the Faculty of Health and Medical Sciences, University of Copenhagen, enables scientists to retrieve molecular evidence to accurately reconstruct human evolution from further back in time than ever before.

The human and the chimpanzee lineages split from each other about 9-7 million years ago. Scientists have relentlessly aimed to better understand the evolutionary relations between our species and the others, all now extinct, in the human lineage.

"Much of what we know so far is based either on the results of ancient DNA analysis, or on observations of the shape and the physical structure of fossils. Because of the chemical degradation of DNA over time, the oldest human DNA retrieved so far is dated at no more than approximately 400.000 years," says Enrico Cappellini, Associate Professor at the Globe Institute, University of Copenhagen, and leading author on the paper.

"Now, the analysis of ancient proteins with mass spectrometry, an approach commonly known as palaeoproteomics, allow us to overcome these limits," he adds.

Theories on human evolution

The fossils analyzed by the researchers were found by palaeoanthropologist José María Bermúdez de Castro and his team in 1994 in stratigraphic level TD6 from the Gran Dolina cave site, one of the archaeological and paleontological sites of the Sierra de Atapuerca, Spain.

Initial observations led researchers to conclude that Homo antecessor was the last common ancestor to modern humans and Neanderthals, a conclusion based on the physical shape and appearance of the fossils. In the following years, the exact relation between Homo antecessor and other human groups, like ourselves and Neanderthals, has been discussed intensely among anthropologists.

Although the hypothesis that Homo antecessor could be the common ancestor of Neanderthals and modern humans is very difficult to fit into the evolutionary scenario of the genus Homo, new findings in TD6 and subsequent studies revealed several characteristics shared among the human species found in Atapuerca and the Neanderthals. In addition, new studies confirmed that the facial features of Homo antecessor are very similar to those of Homo sapiens and very different from those of the Neanderthals and their more recent ancestors.

"I am happy that the protein study provides evidence that the Homo antecessor species may be closely related to the last common ancestor of Homo sapiens, Neanderthals, and Denisovans. The features shared by Homo antecessor with these hominins clearly appeared much earlier than previously thought. Homo antecessor would therefore be a basal species of the emerging humanity formed by Neanderthals, Denisovans, and modern humans," adds José María Bermúdez de Castro, scientific co-director of the excavations in Atapuerca and co-corresponding author on the paper.

Findings like these are made possible through an extensive collaboration between different research fields: from paleoanthropology to biochemistry, proteomics and population genomics.

Retrieval of ancient genetic material from the rarest fossil specimens requires top quality expertise and equipment. This is the reason behind the now 10-years-long strategic collaboration between Enrico Cappellini and Jesper Velgaard Olsen, Professor at the Novo Nordisk Foundation Center for Protein Research, University of Copenhagen and co-author on the paper.

"This study is an exciting milestone in palaeoproteomics. Using state-of-the-art mass spectrometry, we determined the sequence of amino acids within protein remains from Homo antecessor dental enamel. We could then compare the ancient protein sequences to those of other hominins, for example, Neanderthals and Homo sapiens, to determine how they are genetically related," says Jesper Velgaard Olsen.

The dental proteome of Homo antecessor
Frido Welker, Jazmín Ramos-Madrigal, […]Enrico Cappellini
Nature (2020)

Abstract
The phylogenetic relationships between hominins of the Early Pleistocene epoch in Eurasia, such as Homo antecessor, and hominins that appear later in the fossil record during the Middle Pleistocene epoch, such as Homo sapiens, are highly debated1,2,3,4,5. For the oldest remains, the molecular study of these relationships is hindered by the degradation of ancient DNA. However, recent research has demonstrated that the analysis of ancient proteins can address this challenge6,7,8. Here we present the dental enamel proteomes of H. antecessor from Atapuerca (Spain)9,10 and Homo erectus from Dmanisi (Georgia)1, two key fossil assemblages that have a central role in models of Pleistocene hominin morphology, dispersal and divergence. We provide evidence that H. antecessor is a close sister lineage to subsequent Middle and Late Pleistocene hominins, including modern humans, Neanderthals and Denisovans. This placement implies that the modern-like face of H. antecessor—that is, similar to that of modern humans—may have a considerably deep ancestry in the genus Homo, and that the cranial morphology of Neanderthals represents a derived form. By recovering AMELY-specific peptide sequences, we also conclude that the H. antecessor molar fragment from Atapuerca that we analysed belonged to a male individual. Finally, these H. antecessor and H. erectus fossils preserve evidence of enamel proteome phosphorylation and proteolytic digestion that occurred in vivo during tooth formation. Our results provide important insights into the evolutionary relationships between H. antecessor and other hominin groups, and pave the way for future studies using enamel proteomes to investigate hominin biology across the existence of the genus Homo.

Teeth of Homo antecessor shed light on trends in Pleistocene hominin dental evolution
More information: The dental proteome of Homo antecessor, Nature (2020). DOI: 10.1038/s41586-020-2153-8 , nature.com/articles/s41586-020-2153-8