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Journal of Phonetics 35 (2007) 564–581

Letter to the Editor

The vocal tract of newborn humans and Neanderthals:Acoustic capabilities and consequences for the debate on the

origin of language. A reply to Lieberman (2007a)

Louis-Jean Boea,b,�, Jean-Louis Heimb, Kiyoshi Hondac, Shinji Maedad,Pierre Badina, Christian Abrye

aICP-GIPSA-Lab, Institut National Polytechnique de Grenoble, Universite Stendhal, CNRS UMR 5009, Grenoble, FrancebPrehistoire et Paleoanthropologie, Museum National d’Histoire Naturelle, CNRS UMR 5198, Paris, France

cATR Human Information Science Laboratories, Kyoto, JapandTSI Signal-Images, Ecole Nationale des Telecommunications, CNRS UMR 5141, Paris, France

eUniversite Stendhal, Grenoble, France

Received 22 July 2005; received in revised form 14 June 2007; accepted 14 June 2007

1. Introduction

Our work casts doubt on fundamental aspects of Lieberman’s theory on emergence of speech and vocaltract architecture. While our results do not show that Neanderthals were able to speak, they show that theirvocal tracts would not have prevented them from doing so. By minimizing the importance of vocal tractgeometry, our work shifts the debate on the emergence of speech to the cognitive capacity for control of thespeech organs (tongue, lips, jaw, larynx), capacity for learning and for cross-modal, acoustic–visual imitationand the capacity for associating sound with meaning.

2. Recalling the basic arguments

The theory that Philip Lieberman has developed with Edmund Crelin for over 30 years presents two seriesof acoustic and anatomical arguments:

(1) The many anatomical similarities of the base of the skulls of human newborns and of Neanderthals areclaimed to be at the origin of the similarity of their vocal tracts and of a common characteristic: the small sizeof their pharynxes due to a hyoid bone much higher than that of an adult human.

We can now demonstrate that the skeletal features of Neanderthal show that his supralaryngeal vocalapparatus was similar to that of a Newborn human (y). The high position of the opening of the larynx intothe pharynx in Newborn and apes is directly related to the high position of the hyoid bone; therefore, the

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�Corresponding author. ICP-GIPSA-Lab, Institut National Polytechnique de Grenoble, Universite Stendhal, CNRS UMR 5009,

Grenoble, France.

E-mail address: [email protected] (L.-J. Boe).


opening of the larynx into the pharynx is in high position in Neanderthal. (Lieberman, 1972; Lieberman &Crelin, 1971, p. 77)

(2) This characteristic would make it impossible to produce the complete range of speech sounds, notablythe three extreme ‘‘point’’ or ‘‘quantal’’ vowels [i a u] found in almost all the world’s spoken languages.A lowered larynx and so a large pharynx is thus considered by Lieberman and Crelin to be a key anatomicalprerequisite for modern human speech. Apes and human newborns do not have and Neanderthals did nothave the anatomical prerequisites for producing the full range of human speech:

Even if [Neanderthal] were able to make optimum use of his speech-producing apparatus, the constraintsof his supralaryngeal vocal tract would make it impossible to produce ‘articulate’ human speech, i.e. thefull range of phonetic contrasts employed by modern man. (Lieberman, 1972; Lieberman & Crelin, 1971,p. 92–93)

Thus, according to Lieberman, Neanderthals therefore could not produce ‘‘human speech’’, and this wasprobably one of the causes for their extinction:

Thus I propose that the extinction of Neanderthal Hominids was due to the competition of modern humanbeings who were better adapted for speech and language. (Lieberman, 1984, p. 329)The extinction of Neanderthal hominids may derive from their having lacked human speech. (Lieberman,1991, p. 76)

This theory is attractive for explaining the lack of speech in apes and the (relatively) slow appearance of awell-formed vowel system in human babies, and it is widespread (Boe, 2001), having been adopted by manyauthors (Abitbol, 2005; Bradshaw, 1997; Carre, Lindblom, & MacNeilage, 1994; Chaline, 1994; Clark, 1980;Crystal, 1987; Fitch, 2000; Heuvelmans & Porchnev, 1974; Holden, 1998, 2005; Holloway, 1999; Laitman,1986; Laitman, Heimbuch, & Crelin, 1979; Laitman & Reindenberg, 1988; Leakey, 1984; Lewin, 1984;Lieberman, McCarthy, Hiiemae, & Palmer, 2001; de Lumley, 1998; Poitrenaud & Delobre, 2000; Reichholf,1990; Segui & Ferrand, 2000; Senecail, 1979; Shreeve, 1995; Stringer and Gamble, 1993; Vauclair, 1992).

In a series of papers (Boe & Maeda, 1998; Boe, 1999; Boe, Maeda, & Heim, 1999; Heim, Boe, & Maeda,2000; Menard & Boe, 2000; Boe, Heim, Honda, & Maeda, 2002; Heim, Boe, & Abry, 2002; Menard, Schwartz,Boe, Kandel, & Vallee, 2002; Schwartz, 2003, 2004; Boe et al., 2004; Menard et al., 2004; Boe, Heim, Badin, &Abry, 2004; Boe, Heim, Austessere, & Badin, 2005; Boe et al., 2007; Granat et al., 2007) we have:

(1) Proposed a method of reconstructing the vocal tract using the bone structure of the head and the cervicalvertebrae. The method can be applied to present-day speakers but also to Neanderthal fossils or to those ofthe Paleolithic era. Our suggestions complement recently proposed bone reconstructions (Granat & Peyre,2004; Ponce de Leon & Zollikofer, 1999; Sawyer & Maley, 2005; Zollikofer, Ponce de Leon, Martin, &Stucki, 1995).

(2) Adopted the Honda and Tiede (1998) index; a simple geometric ratio, which allows comparison of theanatomical proportions of the oral and pharyngeal parts of the non-human primate, Neanderthal andmodern human vocal tracts, taking into account differences in age and sex. According to this index, theNeanderthal vocal tract is comparable to that of a 10-year old human child.

(3) Shown that the production of the extreme vowels [i a u] does not depend on this index, but mainly on theability to control the jaw, the tongue and the lips, which together account for the vowel configurations ofthe front and back cavities of the vocal tract.

(4) Developed a realistic model of the growth of the vocal tract, from birth to adulthood, for men and women,which demonstrates the same production capacity with respect to the vowel space, regardless of the age orsex of the speakers, thus confirming for newborns the pioneering modeling work of Goldstein (1980).

(5) Proposed that, in order to identify a vowel produced by different vocal tracts, listeners carry out aperceptual normalization which uses formants and fundamental frequency. These parameters allow one toassess, to a certain extent, the age, sex and thus the size of the vocal tract of the speaker (Menard et al.,2002), thus furthering the work of Fant, Carlson, and Grandstrom (1974), Traunmuller (1981), Syrdal andGopal (1986), Traunmuller and Lacerda (1987) and Hoemeke and Diehl (1994).

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3. The historical background

Lieberman’s (2007a) Letter to the Editor (hereafter Letter) and a previous paper (Lieberman, 2002) containmisinterpretations of our claims, data and modeling, as well as of that of other authors. Our aim in this reply isto respond to these.

The Letter downplays the role of anatomical reconstruction of the supralaryngeal vocal tract (SVT)highlighted in Lieberman’s early articles, and re-casts the original claim about the descent of the larynx as aclaim about the primacy of tongue root positioning (see also Lieberman, 2002), thus reflecting the fact thatboth of the original hypotheses concerning the position of the Neanderthal hyoid bone and the importance oflarynx descent per se have now been called into question (Fitch, 2002; Fitch & Reby, 2001; Nishimura, 2004;Nishimura, Mikami, Suzuki, & Matsuzawa, 2003; Weissengruber, Forstenpointner, Peters, Kubber-Heiss, &Fitch, 2002). Specifically, it is stated that:

The key factor, thus, is not the descent of the larynx. The descent of the tongue in the pharynx enables thehuman SVT to produce either constricted or open pharyngeal airways. (Lieberman, 2007a, p. 553)

From an anatomical point of view, however, as recognized by Lieberman, it is difficult to conceive how thetongue could descend in the pharynx without interfering with the vertical position of the larynx:

While the tongue is positioned almost entirely in the mouth in other species and in human neonates, itmoves down into the pharynx, carrying the larynx down [our emphasis] (Lieberman, 2007a, p. 560)

With our current state of knowledge, it is difficult to establish if, during evolution, the tongue has pushedthe larynx into a low position (see Negus, 1949, pp. 25–26), or if the larynx descent per se (due perhaps to theerect posture) is the cause of the descent of the tongue. In either case, our work shows that the increase in sizeof the pharynx which resulted did not modify the potential vocalic sound-producing capacities of the vocaltract.

We would also highlight a problem about the presentation in the Letter of ‘‘the historical background’’ tothese issues. Referring (amongst others) to Negus (1949), Lieberman (2007a) writes:

In contrast, the tongues of non-human primates and human newborns are positioned almost entirely withintheir mouths and cannot produce these [i a u] SVT area functions. (Lieberman, 2007a, p. 553)

However, Negus, in his classic book The Comparative Anatomy and Physiology of the Larynx (1949),a ‘‘condensed and readjusted’’ reprint (author’s preface) of his earlier book The Mechanism of the

Larynx (Negus, 1929), never evoked the ‘‘area functions’’ of the [i a u] vowels. In fact, for Negus,the vocal tract geometry was not a requirement to produce modern human speech, as Lieberman suggestsabove:

The disproportion between oral and pharyngeal cavities allowed for fewer variations in quality of voicethan are now possible; distinctions between individual voices would, therefore, have been less pronounced.Although early Man was provided with all the necessary requirements for speech as modern Man uses it,his intelligence was too low an order to allow his taking much advantage of his physical possibilities.(Negus, 1949, p. 200)

Lieberman’s approach also leads him to appeal to Kuhl’s work on speech development (Kuhl, Williams,Lacerda, Stevens, & Lindblom, 1992) in support of his stance. However, in reality, the ‘‘magnet effect’’ cannever lead us to suggest that phoneticians cannot distinguish an [I] from an [i]. Furthermore, it is well knownthat there is no categorical perception effect for vowels (Repp, 1984), and that the well-trained ear candistinguish between two subtly different qualities.

4. Lieberman’s (2007a) analysis of Boe et al. (2002)

The Letter misinterprets our claim about our simulations of the Neanderthal SVT. Contrary to what isclaimed, the variable linear articulatory model (VLAM, developed by Maeda and used in Boe, 1999; Boe &

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Maeda, 1998) does not simply replicate a model adult man, but rather models a vocal tract from birth toadulthood:

The Boe et al. (1999, 2002) studies replicate these findings [the relationship that holds between SVT shapesand formant frequency] since (y), they model adult human SVTs producing the area functions normallyused to produce human speech. (Lieberman, 2007a, p. 553)

In addition, we have never claimed or written that Neanderthal had the same SVT as an adult human,contrary to the letter’s assertion:

Since recent papers, such as Boe et al. (1999, 2002), continue to claim that La Chapelle-aux-SaintsNeanderthal fossil had an adult human SVT (y) (Lieberman, 2007a, p. 557)

Following Honda and Tiede (1998), we used for our model a larynx height index (LHI) ratio betweenlaryngeal height (LH, the ‘‘vertical’’ part of the vocal tract, roughly the height of the pharynx) and palataldimension (PD, the ‘‘horizontal’’ part of the SVT) (roughly the SVTh and SVTv according to Lieberman’sdesignations) and we adopted the values shown in Table 1.

There is a misconception manifested in the arguments related to Figure 1 of the letter (originally publishedin Lieberman, 1984, p. 296). Lieberman’s reconstructed vocal tract has an excessively long SVTv with anunrealistically low larynx position. This is a direct consequence of the hypothesis of a 1:1 ratio between SVThand SVTv. We estimate the correct ratio to be around 0.80 (see Table 1), which sets the larynx at a realisticposition. Lieberman appears to assume that the 1:1 ratio is the necessary condition for having the correct threepoint vowels [i a u] (Lieberman, 1984, pp. 290–296, 1991, pp. 67–69, 1998, pp. 92–94, 2007a, see legend ofFigure 1). With that ratio, the Neanderthal larynx is excessively low. The actual Neanderthal’s larynx wasmuch higher, resulting in a ratio of less than one, and Neanderthal therefore could not have had the correctpoint vowels. The acoustic theory of speech production (Fant, 1960) and our simulations (Boe et al., 2002)have shown that the 1:1 ratio is not the necessary condition for the production of the point vowels [i a u], if anappropriate motor control capacity for articulation in Neanderthals can be assumed.

The following claim is also not correct:

The claims of Boe et al. (1999) to the effect that newborn human infants can, and Neanderthals could,produce the vowel [i] are based on their modeling a supposed ‘newborn’ vocal tract that in actuality issimilar to that of a 5-year-old human child who has already attained an adult-proportioned SVT in whichthe pharynx and oral cavities have almost equal length: a criterion necessary to produce the vowel [i].(Lieberman, 2002, p. 56)

In fact: (1) to simulate the vocal tract of a newborn, we used an LHI of 0.60 and not that of a 5-year oldchild, (2) the vocal tract of a 5-year old child does not at all contain the same proportions as an adult vocaltract, as data from Goldstein (1980) and Fitch and Giedd (1999) (presented in Tables 2 and 3) show.

The mean values and ANOVA results showing changes in the pharynx are highly significant (po0.0001 forthe Fisher’s PLSD values) in the lengths of segments of pharynx across the three age groups. ‘‘Pre-’’ pubertalchildren are less than 10.3 years in age, ‘‘post-’’ pubertals are older than 14.5 and ‘‘peri-’’ pubertals are in

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Table 1

Values of vertical larynx height (LH), horizontal palatal distance (PD), mean vocal tract length and larynx height index, for humans at

different ages and for Neanderthal adults (revised from Boe et al., 2002 to take into account the dimensions for La-Chapelle-aux-Saints

and La Ferrassie)

LH (cm) PD (cm) Vocal tract length (cm) LHI LH/PD

Modern newborn 2.63 4.34 7.7 0.60

Four-year old baby 4.51 5.70 10.8 0.79

Ten-year old child 5.75 6.57 12.9 0.88

Adult woman or 16-year old boy 7.40 7.80 15.7 0.95

Adult man (21 years) 8.70 8.70 17.8 1.00

Neanderthal (adult male) 8.80 11 22 0.80

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between the two ranges. Therefore the differences in segment length between 5-year old children and adults areagain highly significant.

LHI allows us to anatomically compare humans, Neanderthals and chimpanzees and to account fordifferences in age and sex, in short to quantify the phylogenesis and the ontogenesis of the supralaryngealcavities (Table 4). But this index is not relevant for predicting the speech capacity of a given vocal tract. Infact, as we will see, at birth, children are able to produce the three point vowels [i a u], and throughoutdevelopment the space of these vowels remains just as differentiated.

Having clarified the elements of the debate, we now present the principal anthropological and acousticarguments on the basis of which we refute Lieberman’s (2007a) stance.

5. Anthropological arguments

5.1. The reconstruction of the skull base

At the beginning of the 20th century, Marcellin Boule, the director of the Institut de Paleontologie Humainein Paris, could only rely on a very few elements to accurately reconstruct the skull base (Boule, 1911–1913). Hearrived at the conclusion that Neanderthal man was closer to the chimpanzee than to modern man andtherefore featured forward-tilted head position (see Fig. 1):

This set of characteristics, which are nevertheless found to a lesser degree, in the skeletons of inferior racesof Man, Australians, Boschimans, and that one observes, for example, very clearly in the Venus Hottentote,particularly brings our fossil [La Chapelle-aux-Saints] closer together with the anthropoid apes, notablywith the chimpanzee. (our translation) (Boule, 1911–1913)

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Table 2

Length of oral, pharyngeal cavities and of the vocal tract (in cm) proposed for males by Goldstein (1980, p. 186) and corresponding LHI.

(These authors use more detailed segments)

Age (years) Oral cavity Pharynx cavity Vocal tract LHI

0 5.28 2.67 7.95 0.50

1 5.67 3.63 93.3 0.64

5 6.48 4.55 11.03 0.70

Adult 8.07 8.87 16.93 1.10

These authors use more detailed segments.

Table 3

Data extracted from Fitch and Giedd (1999, p. 1515): age category of individual vocal tract segment lengths (in cm)

Age Lips Tongue

blade

Tongue

dorsum

Velum Pharynx Length

(seg.)

Oral seg.:pharyngeal

seg.ratio

2–4 years 1.22 1.76 2.22 2.54 2.63 10.36 0.40

5–6 years 1.33 1.80 2.16 2.57 3.21 11.08 0.49

Adult men 1.45 2.55 2.68 3.40 6.04 16.12 0.70

Table 4

The larynx height index for modern human, Neanderthal and chimpanzee

LHI 1.00 0.95 0.88 0.80 0.60 0.50

Modern Man Woman 10 yr 4 yr Newborn

Neanderthal Adult Newborn

Newborn Adult

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Boule calculated an excessively advanced center of gravity for the head, giving the basion and the occipitalhole an overly retracted position (of around 4mm) linked to the position of the body, which he assumed to bebent (Heim, 1986, 1989, 1990). In their incisive critique of Boule’s description of the La Chapelle-aux-Saintsfossil that Lieberman and Crelin (1971, p. 203, 1972, p. 76) considered as ‘‘perhaps the archetypal example of‘classic’ Neanderthal man’’ (p. 203), Sawyer and Maley (2005) point out that:

In his highly detailed and influential monograph, Boule, expounded notions that underpinned theerroneous image that Neanderthals were nothing more than slouched, bent-kneed, primordial bipeds withnon lordotic neck curvature. Furthermore, he implied that these hominids had a rudimentary mentalcapacity and thus were unlike predecessor to modern humans. In the end, Boule managed to entrench anerroneous stereotype of Neanderthals physical attributes and behavior, a stereotype that continues tosurface in today’s popular culture. (Sawyer and Maley, 2005, p. 23)

Lieberman and Crelin therefore used an erroneous description and reconstruction of the base of the skullfor their reconstruction of the Neanderthal SVT. This has not gone unnoticed:

Various anatomists and anthropologists were quick to criticize Lieberman and Crelin. Their first error layin accepting Boule’s reconstruction of the base of the skull, which was abnormally flat (y). Jean-Louis-Heim a paleoanthropologist at the Musee de l’Homme, took the opportunity to clean off the antique glueand to reassemble the fragment anew. (Trinkaus & Shipman, 1993, p. 354)

5.2. The reconstruction of the hyoid and larynx position

The arrangement of the hyoid bone and the larynx presented by Lieberman (1972) and Lieberman andCrelin (1971) is unrealistic; they are much too high with respect to the base of the jaw:

Crelin also made a serious mistake in positioning the larynx; (y) But the largest problem in thereconstruction by Crelin and Lieberman lay in the position of the hyoid, a small bone above the larynx towhich the tongue muscles attach. As reconstructed, Neanderthals were not only unable to talk, variousanthropologists and anatomists observed, they were also unable to swallow or open their mouths.(Trinkaus & Shipman, 1993, pp. 354–355)

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Fig. 1. Left: the head and neck reconstruction of the La Chapelle-aux-Saints Neanderthal directed by Boule (Institut de Paleontologie

Humaine in Paris) and realized by the sculptor M. Joanny-Durand in 1921. This reconstruction has influenced that of the Field Museum of

Natural History of Chicago by the sculptor Frederick Blaschke in 1927 under the direction of the director Henry Field (right) (reprinted

with permission from the Field Museum). Note the forward head tilts close to that of chimpanzee.



In fact, the hyoid bone is inserted into the digastric ‘‘hammock’’ and thus lies below the body of the jawbecause it extends, in an angled form, from the digastric fossa, on the base of the mandible, to the mastoidprocess. As Granat and Peyre (2004, p. 156) correctly describe:

To estimate the probable position of the hyoid bone and of the larynx for each species of the genus Homo, itis indispensable to first be able to evaluate the distance available between the plane of the base of themandible and the distal face of the last cervical vertebra used as a marker of the beginning of the thoraciccage. (our translation)

The biometric data from La Ferrassie 1 (Heim, 1976) and from Kebara 2 (Arensburg, 1991) allow us to usethe dimensions of the cervical column of two Neanderthals and to compare them with those of present-daypopulations and to estimate the lower limit of the lowest position of the larynx:

The cervical vertebrae [of La Ferrassie 1] are complete and remarkably well preserved (y) The sum of theheights of the anterior face of the vertebral bodies is 98.5 cm, while the total height of the cervical column,whose intervertebral discs have been replaced by a thin layer of plastiline, reaches approximately 11 cm. Wecan note that these two figures differ very little from those that we have measured from isolated vertebraeand from cervical columns of French people (99mm and 104mm). (our translation) (Heim, 1976, p. 311)

The discovery of the hyoid bone of the Kebara man (Arensburg, 1991: Arensburg et al., 1985, 1989;Arensburg, Schepartz, Tillier, Vandermeersch, & Rak, 1990) again allowed us to make progress in solving thepuzzle of the reconstruction of the Neanderthal vocal tract:

The bone is almost identical in size and shape to the hyoid of present-day populations, suggesting that therehas been little or no change in the visceral skeleton (including the hyoid, middle ear ossicles, andinferentially the larynx) during the past 60,000 years of human evolution. (Arensburg et al., 1989, p. 758)

The reconstruction work of Granat and Peyre (2004) on the larynx position of the genus Homo fromanatomical, embryological and physiological data and that of Sawyer and Maley (2005) allow us to propose amore realistic arrangement of the hyoid–larynx (Fig. 2).

And we are able to propose a reconstruction of a plausible vocal tract for La Ferrassie 1 (Fig. 3).

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Fig. 2. Position of the hyoid and larynx for Neanderthal. Left: redrawn from Lieberman (1972) and Lieberman and Crelin (1971,

Figure 24). Right: based on the reconstruction proposed by Granat and Peyre (2004) for La Ferrassie 1; the hyoid bone is located on a

parallel plane to the plane of Frankfort (orbitale–porion) at the level of the gnathion.



6. Acoustic arguments

6.1. On the acoustics of vowel production

Another critical difference between our work and Lieberman’s relates to the understanding of the acoustictheory of vowel production. For vowels, Fant (1960) proposed schematizing the vocal tract and modeling it byfour cylindrical tubes, which represented the back cavity, the constriction, the front cavity and the labial horn.For [i] and [a], this simplification can even be reduced to two tubes (Stevens, 1972, 1998) (Fig. 4).

The geometric characteristics that have the most important consequences for formant values are theposition and the area of the constriction of the inside of the part of the vocal tract that characterizes the placeof articulation. It is important to note that the cavities do not necessarily correspond to an anatomical divisioninto oral and pharyngeal parts.

Using basic acoustic principles, it is possible to estimate the first three resonance frequencies (F1, F2 andF3). Vocal tracts thus schematized can be considered to be Helmholtz resonators, as tubes open at either oneor both ends that resonate in multiples that are halves or quarters of a wavelength (l/2 and l/4) (Table 5). Theformant patterns of those three point vowels are well characterized by different combinations of resonancemodes that make their distinctiveness robust.

From an acoustic point of view, the angle between the oral and pharyngeal cavities, which depends mainlyon head tilt, has only a limited influence (affecting formant values by only a small percentage) on the acousticproperties of vowels (Sondhi, 1986). Globally, the resonance frequencies of a vocal tract are inverselyproportional to its length. Thus, with an average vocal tract length about half the size (8 cm) of an adulthuman (17 cm), an infant a few months old produces vowels whose formants are two times greater than thoseproduced by an adult. This transposition preserves the ratio between formant frequencies and preserves thedifferences when the frequencies are expressed in Bark (or in ERBs). A given variation in the ratio k of thelength of a resonance cavity which is a multiple or (sub-multiple) of the wavelength produces a variationinversely proportional to l in the formants affiliated with this cavity. This is also the case for a Helmholtzresonator (for example, that formed by the two tubes of the simplified [i] vowel), as long as the ratio betweenthe two tubes is preserved. To identify the vowels that come from vocal tracts of different lengths, one canhypothesize that listeners carry out a perceptual normalization that takes into account other typicallycorrelated properties such as the frequency of vibration of the vocal folds (which tends to be higher for shortervocal tracts in modern humans). In conjunction with the formants, this fundamental frequency allows thelistener to estimate, to a certain extent, the age and sex, and therefore the vocal tract size of the speaker(Menard et al., 2002).

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Fig. 3. Reconstitution of the vocal tract shape for [i], based on an assembly of the skull of La Ferrassie 1, the cervical vertebrae and the

Kebara hyoid bone (radiography and photography from Le Musee de l’Homme, Paris), made by Granat and Peyre (2004); note the shape

of the hard palate on the X-ray (right).



The quantal vowel [i] is basically characterized by a low F1 and high F3. Basic vocal tract acoustics showsthat, whatever the anatomical size of the SVT, and whether an oversimplified or highly sophisticated model isused, there is only a single solution that generates a vowel with the very high F3 of the typical [i]. In thisconfiguration, a constriction tube is formed by fronting the grooved tongue against the hard palate; as a directconsequence, the length of the back cavity will always be appropriate for producing an F2 at a sufficiently highfrequency. This configuration also ensures a resonance of the Helmholtz resonator formed by the back cavityand a front constriction low enough to be typical of the F1 of [i]. Thus, with a constriction of 5.6 cm in length,an area of 0.65 cm2, and a back cavity volume of 60 cm3 (or a length of 8.3 cm with an average area of 7.2 cm2),an adult man indeed produces an [i] with an F1 of 245Hz and an F3 around 3100Hz (and an F2 of 2100Hz),which is the acoustic goal to be achieved. The two remaining quantal vowels can be produced with nodifficulty with two Helmholtz resonators for [u] and with a horn-shaped open vocal tract for [a].

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Fig. 4. Schematic representation of three vowels [i a u] with two or four tubes (original drawings of the vocal tract reprinted with the

permission of Sophie Jacopin, http://www.illustration-medicale.com/).

Table 5

Cavity-formant affiliations for the vowels [i a u], from the simplified representations of Fig. 4

F1 F2 F3

[i] Helmholtz: palatal constriction+back cavity l/2 back cavity l/2 palatal constriction

[a] l/4 front cavity l/4 back cavity 3l/4 front cavity

[u] Helmholtz: velar constriction+back cavity Helmholtz: labial constriction+front cavity l/2 back cavity

Note: According to the respective volumes of the front and back cavities, there can be changes in the affiliations of the F1 and F2 of [a] and

[u] (Boe, Perrier, & Bailly, 1992).



6.2. Producing quantal vowels

In the discussion about how to produce quantal vowels, the Letter suggests that F2 in [i] varies minimally asa function of the constriction degree and refers to a prediction by Beckman et al. (1995) about a 50Hz F2 shiftfor constrictions varying between 0.1 and 0.69 cm2. Actually, this prediction cannot be found in thecorresponding paper. Rather, Beckman and colleagues recall that constriction degree is a major determinantof quantal vowels:

Many vowels have target articulatory constrictions that are more or less quantal, in the sense thatconstriction degree seems to be controlled more precisely than constriction location (Beckman et al., 1995,p. 489)

This suggests that the control of constriction size may have been consistently underestimated by Lieberman.To prove that newborns and Neanderthals could not produce the [i], [a] and [u] vowel contrasts, Lieberman

(1972) and Lieberman and Crelin (1971, pp. 86–88) started from reconstructions of the SVT. They thenmeasured cross-sectional areas. These measurements gave a ‘‘neutral area function’’ that they ‘‘perturbedtowards area functions that would be reasonable if a Newborn or a Neanderthal vocal tract attempted toproduce the full range of human vowels,’’ (Lieberman, 1972; Lieberman and Crelin, 1971, pp. 87–88), namelythe [i], [a] and [u]. In doing so, they worked with the area functions proposed by Fant (1960) for [i], [a] and [u],but they did not quantitatively state the constraint or rules of the perturbation of the uniform area functionthat they applied. Fig. 5 presents Fant’s area functions and those proposed by Lieberman and Crelin.

The small vowel triangle obtained by Lieberman and Crelin is due to the fact that they modified the threearea functions without apparently taking into account essential facts about the acoustic theory of speechproduction. It turns out that the vowel [a] is the only realistic vowel, since it is naturally characterized by apharyngeal constriction. As a matter of fact, the area function of this vowel roughly matches that proposed byFant. But their strategy of emphasizing the match to constriction location rather than to constriction degreewas the opposite of what they needed to do to capture the properties of the quantal vowels [i] and [u].Lieberman and Crelin do not appear to have drawn on knowledge about the resonator, which allows one tohandle the length of the constriction and the area and volume of the back cavity at the same time. The backcavities of these two vowels are much too small in volume for the production of a low F1. In retaining for [i] apalatal constriction with sufficient length (at least 5 cm) and an area sufficiently small (adjusted according tothe volume of the back cavity), Lieberman and colleagues would have obtained a much more differentiatedvowel triangle.

Furthermore, Lieberman and Crelin adopted for Neanderthal a very strong constraint by limiting the areafunction in the pharynx region (between 2 and 5 cm above the glottis) to 3.5 cm2 (see Fig. 5). This is notcompatible with the capacity for tongue protrusion observed for newborns a few hours after birth (Meltzoff,2000; Meltzoff & Moore, 1977, 1983, 1989), and for 3-day-old macaques (Ferrari et al., 2006), which canbe assumed for Neanderthal as well. In fact, the area functions proposed by Lieberman and Crelin couldonly produce mid vowels (those between [i] and [a] and between [u] and [a]) rather than the extreme vowels[i] and [u].

6.3. Vowel space and SVT modeling

The maximal vowel space (MVS) of a given speaker (Bonder, 1982; Liljencrants & Lindblom, 1972) can bedefined as the n-dimensional space of the first n formants of all possible vocalic sounds that can be producedby that speaker. The use of an articulatory model allows an exhaustive determination of the borders of thatspace. It is possible to produce the maximal F1–F2–F3 acoustic space of a model by scanning the entire inputspace of each articulatory control parameter, while satisfying the conditions necessary for vocalic production.The fact that all vowels are necessarily located within the F1–F2–F3 triangle is due to the basic acousticproperties of a single tract (Boe, Perrier, Guerin, & Schwartz, 1989). If one considers, following Liljencrantsand Lindblom (1972), that the vowels [i a u] are located within the MVS in such a way as to maximize thedistances between vowels, it is possible to characterize in the F1–F2–F3 acoustic space the three point vowels(Schwartz, Boe, Vallee, & Abry, 1997). Due to the geometric shape of the MVS, the vowel [i] is characterized



by a maximal F3, resulting in a minimal F1 and a maximal F2; the vowel [a] corresponds to a maximal F1; thevowel [u] is produced with a minimal F2, resulting in a minimal F1 value (Fig. 6).

Using the MVS in such a way is more reliable than simply using three unique examples of the point vowels[i], [a] and [u] which are not guaranteed to be located at the real limits of the potential triangle of a given vocaltract. As further evidence of this, we have positioned the three vowels proposed for [i a u] by Lieberman andCrelin with respect to the Peterson and Barney (1952) data. As predicted by Lieberman and Crelin, it appearsthat the estimated Neanderthal vowel triangle is reduced, but it is difficult to place this triangle with respect tothe vowel spaces of men, women or children (Table 6, Fig. 7).

We have generated the MVS (using Badin & Fant, 1984) (Fig. 8) of the classical four-tube model of Fant(1960). At the extremities of the F1–F2 and F2–F3 spaces, the area functions correspond well to the simpleprototypes for adult men shown in Fig. 4. This shows that even a model as simplified as this four-tube model iscapable of generating the three vowels [i a u] with the same contrasts as a more anthropomorphically correctmodel. The chimpanzee and the baby could very well produce these vowels whatever the size of their pharynx.If they do not, it is first and foremost a problem of control of the tongue, the jaw and the lips for assuring agood distribution between the constriction and the front and back cavities.

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Fig. 5. Area functions presented by Lieberman and Crelin as the ‘‘best match’’ for Neanderthal trying to produce the human [i], [a] and [u]

contrasts with a small pharyngeal cavity (solid lines). Superimposed, the corresponding Fant’s (1960, p. 115) area functions (staircase).



Speech development entails both maturation of motor control abilities and major anatomic modifications,and their role is difficult to disentangle one from the other. This is also the case in the course of phylogeny. Inthis context, an anthropological SVT model is a basic tool in attempting to partition what can be attributed tocontrol and what arises from morphology.

In pursuit of this we have used a modified version (Boe et al., 2007) of the VLAM, an articulatory model (Boe,1999; Boe & Maeda, 1998) for simulation of vocal tract growth: this model can be adjusted and positioned withregards to the skull architecture, according to data provided by Fenart (2003). Fig. 9 shows for a newborn andan adult male that this vocal tract model can fit well the hard palate and the cervical vertebrae. We thencalculated the shift and size of the vowel space as a function of age for the point vowels [i a u] (Boe et al., 1999;Menard, 2002; Menard et al., 2004, 2002). The resulting values were found to be consistent with the dataavailable in the literature for vocal tract length (Fitch & Giedd, 1999; Goldstein, 1980; Kasuya, Suzuhi, & Kido,1968; Story, Titze, & Hoffman, 1996; Vorperian, 2000; White, 1998; Yang & Kasuya, 1994) and for formants(Eguchi & Hirsh, 1969; Fant, 1973; Hillenbrand, Getty, Clark, & Wheeler, 1995; Huber, Stathopoulos, Curione,Ash, & Johnson, 1999; Lee, Potamianos, & Narayanan, 1999; Peterson & Barney, 1952).

Our results confirm the thesis of Goldstein (1980) who had used the geometric articulatory model ofMermelstein (1973) to propose articulatory and acoustic prototypes of the point vowels /i a u/ for male andfemale newborns and to show that:

The new estimate indicates that the newborn is capable of producing /i/, />/, and /u/, whereas the estimatesof Lieberman would indicate that it is not. (Goldstein, 1980, p. 202)

And she concluded:

Since the vowels /i/, /æ/, and /u/ can be synthesized by a model which is anatomically correct for infants,one can postulate that newborns are not prevented from speaking because of the anatomy of their vocal

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(Schwartz, Boe, & Abry, 2007).

Table 6

Formant values F1, F2, F3 for the vowels [i a u] corresponding to the reconstruction of the vocal tract of La Chapelle-aux-Saints skull

proposed by Lieberman and Crelin calculated using the area function (using Badin & Fant, 1984)

F1 (Hz) F2 (Hz) F3 (Hz)

[i] 524 2038 3016

[a] 846 1655 2880

[u] 462 807 2974



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Fig. 8. Maximal vowel space generated by the four-tube model of Fant (1960) in the F1–F2 and F2–F3 spaces for 20,000 vowel-like

articulations. At the extremities of the spaces, the vowel [i], [a] and [u] and the corresponding two-tube and four-tube configurations which

correspond to the four-tube prototypes of Fig. 4.

500100015002000250030003500

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Lieberman and Crelin (1971) using a frequency domain simulation (Badin & Fant, 1984). The [i], [æ], [>] and [u] quadrilaterals (in gray) for

adult men (upper right), adult women (middle) and children from Peterson and Barney (1952).



tracts. Rather, their development of speech is probably linked to the development of proprioception,neuromuscular control, and intellectual capacity. (Goldstein, 1980, p. 214)

The results obtained with VLAM, the growth model, show that the MVS of newborn infants is potentially(at least) the same as that for adult males and it allows us to propose [i a u] midsagittal prototypes. If wecompare the formant values of these vowels with the Kuhl and Meltzoff (1996) data on the vocalizations of12–20 week-old infants, we observe that they are fully compatible. We can thus infer that 20 week-old infantsdo not yet possess control of their tongue and lips, even though they manage to produce differentiated [i]-like,[a]-like, [u]-like vowels; see also Rvachew, Mattock, Polka, and Menard (2006). Recently the VLAM growthmodel was used to induce motor control of tongue, jaw and lips of a robot that models human infants,including those at 20 months, via the analysis of natural vocalizations (Serkhane, Schwartz, & Bessiere, 2005;Serkhane, Schwartz, Boe, Davis & Matyear, 2007).

7. Conclusion: Neanderthal speech–dropping the charges against the vocal tract

With the anthropometric data that we currently have available for the skull and the vertebrae of LaChapelle-aux-Saints, La Ferrassie 1 and Kebara, as well as for the Kebara hyoid bone, it is possible toestimate the limits of a plausible Neanderthal vocal tract. For the pharyngeal part, we must take into accountthe base of the skull, the plane of the base of the mandible, under which the hyoid bone is suspended, and thedimensions of the cervical vertebrae. Compared to modern humans, Neanderthals possessed a vocal tract witha longer palatal section and likely a similar pharyngeal section.

Although reconstructions of the vocal tract are important for physical anthropology and evolution, they donot have crucial consequences for the estimation of the acoustic capacities assumed for a given vocal tract. Infact, what we know of the acoustics of speech and speech modeling show that whatever the relationshipbetween the pharyngeal and oral parts, it is control of the tongue, the jaw and the lips that allows one to

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Fig. 9. Vocal tracts generated by the model (Boe et al., 2007) positioned relative to anthropometric coordinates proposed by Fenart

(2003): (1) vertex, (2) bregma, (3) glabella, (4) nasion, (5) orbitale, (6) center of sella turcica, (7) porion, (8) lambda, (9) opisthocranion,

(10) anterior nasal spine, (11) posterior nasal spine, (12) basion, (13) mastoid process, (14) opisthion, (15) inion, (16) prosthion,

(17) infradentale, (18) pogonion, (19) menton, (20) gonion, (21) upper part of the condyle, (5)–(7). Frankfort plane and we have added

(22) the anterior part of the hyoid bone. Left: newborn, right: adult male. The straight line from the basion (point 12) roughly represents

the position of the anterior part of the cervical vertebrae and its tilt relative to the skull. Note that the distance between pharyngeal wall

and the vertebrae is larger for newborn than for adults, as attested in manuals of anatomy (Negus, 1949, p. 175; Rohen et al., 1999, p. 151).



configure the vocal tract to produce the three vowels [i a u] found in all the world’s spoken languages. Thiscapacity for control adapted throughout the course of ontogenesis to the dimensions of the speech productionorgans permits children, adolescents and adults of either sex and any age to produce a sound system thatmaximizes the perceptual distances between their vowels.

We would suggest that Lieberman’s claims are marred by a series of anatomic (hyoid position), articulatoryand acoustic flaws (mainly confusion between anatomic parts of the vocal tract with front and back cavities ofthe vowel production). If newborn infants had the same sensorimotor (control) capacities as adults, their vocaltracts would allow them to produce an F1–F2–F3 vowel space as extensive as that of their parents. Theysimply need time to acquire and master the relevant control strategies. Endowed with a small pharyngealcavity, newborn chimpanzees exhibit the same vocal tract configuration as newborn infants, although they donot produce vowels. If Neanderthals could not speak, it is unlikely to have been for the articulatory andacoustic reasons advocated by Lieberman; they were physically able to do so. A low larynx (and largepharynx) cannot be considered to be the ‘‘anatomical prerequisites for producing the full range of humanspeech’’ (Lieberman, 1991, p. 67, 1998, p. 94; Lieberman, 1972; Lieberman & Crelin, 1971, p. 97) and there isno reason to believe that the lowering of the larynx and tongue, and the increase in size of the pharynx whichresulted, was a necessary evolutionary pre-adaptation for speech.

With the emergence of speech, we are confronted with problems, with constraints and with limitations thatare not fundamentally related to the geometry and the acoustics of the vocal tract, but which refer to thecapacities of control and learning that are at the heart of the question of the emergence and structuring oflanguage (a point which indeed is reflected in Lieberman’s own work on the neural bases of speech andlanguage; e.g. Lieberman 2006, 2007b).

Acknowledgments

To Jean-Luc Schwartz and Lucie Menard for their comments and helpful criticisms. To Denis Autesserreand Jacques Vauclair for precious information. To Jean Granat and Evelyne Peyre for having shared thefigures from their reconstructions with us. To Philippe Mennecier, director of collections at the Musee del’Homme, Paris, for the head photography and radiography of La Ferrassie 1. To Jerice Barrios (rights andreproductions coordinator, The Field Museum Library, Photo Archives) and to Sophie Jacopin for permissionto reprint illustrations. This research has been partly funded by the French Centre National de la RechercheScientifique (CNRS): Controle oro-facial dans la communication chez les primates humains et non humains:Neandertal, le singe et l’Homme project (managed by Jean-Luc Schwartz, ICP, 2001–2006), within the Originede l’Homme du Langage et des Langues (OHLL) project (managed by Jean-Marie Hombert), and by theEuropean Community EUROCORES program (Orofacial control in communication in human and non-human primates (principal investigator, Didier Demolin, Phonology Laboratory, Brussels, 2002–2006), withinThe Origin of Man, Language and Languages (OMLL) project.

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Author's personal copy ARTICLE IN PRESS - UQAM · Author's personal copy 3. The historical background Lieberman s (2007a)Letter to the Editor (hereafterLetter) and a previous paper