Palatal morphology influences the production of phonemic contrasts (like s-sh)

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Palatal morphology can influence speaker-specific

realizations of phonemic contrasts

Journal: Journal of Speech, Language, and Hearing Research

Manuscript ID: JSLHR-S-12-0217.R1

Manuscript Type: Supplement

Date Submitted by the Author: n/a

Complete List of Authors: Weirich, Melanie; Friedrich-Schiller-Universität Jena, Institute for German Linguistics Fuchs, Susanne; Center for General Linguistics, Phonetics

Keywords: inter-speaker variability, phonemic contrast, sibilant, palate shape

Journal of Speech, Language, and Hearing Research

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Palatal morphology can influence speaker-specific 1

realizations of phonemic contrasts 2

3

Melanie Weirich* 4

*Institute for German Linguistics, Friedrich Schiller Universität Jena 5

Susanne Fuchs o 6

°ZAS – Centre for General Linguistics, Berlin 7

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Corresponding author: 12

Melanie Weirich 13

Institut für Germanistische Sprachwissenschaft 14

Friedrich Schiller Universität Jena 15

Fürstengraben 30 16

07743 Jena 17

Germany 18

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Email: [email protected] 20

Fax: +49-3641-944332 21

Phone: +49-3641-944333 22

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ABSTRACT 1

2

3

Purpose: The purpose of this study is to further explore the understanding of speaker-specific 4

realizations of the /s/-/ʃ/ contrast in German in relation to individual differences in palate 5

shape. 6

Method: Two articulatory experiments were carried out with German native speakers. In the 7

first experiment four monozygotic and two dizygotic twin pairs were recorded by means of 8

electromagnetic articulography. In the second experiment 12 unrelated speakers were 9

recorded by means of electropalatography. Inter-speaker variability in the articulatory 10

distance between the sibilants was measured and correlated with several parameters of the 11

palate shape. 12

Results: Our results are twofold: a) similar palatal morphologies as found in monozygotic 13

twins yield similar articulatory realizations of the /s/-/ʃ/ contrast regarding vertical and 14

horizontal distance of the target tongue tip positions; b) the realization of the contrast is 15

influenced by the palatal steepness, especially the inclination angle of the alveolo-palatal 16

region. Speakers with flat inclination angles mainly retract their tongue to realize the contrast 17

whereas speakers with steep inclination angles additionally elevate the tongue. 18

Conclusions: The articulatory realization of the sibilant contrast is not only influenced by 19

speaker-specific auditory acuity as previously observed but also by palatal shape morphology, 20

which affects the somatosensory feedback speakers receive. 21

22

KEYWORDS: phonemic contrast, sibilant, inter-speaker variability, palate shape 23

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I. INTRODUCTION 1

2

This work investigates inter-speaker variability in speech production. Factors involved in 3

inter-speaker variability are manifold. Ladefoged & Broadbent (1957, p. 98) group them into 4

“idiosyncratic features of a person’s speech” that may “be a part of an individual’s learned 5

speech behaviour” and “anatomical and physiological considerations”. These two influencing 6

parameters can also be specified as non-biological determinants and biological determinants. 7

Non-biological determinants affecting inter-speaker variability incorporate speakers’ 8

language, dialectal background and speech acquisition process but also their social 9

environment and social identity. Regarding the acquisition of language, Chambers (2003) 10

stated that “when children acquire their mother tongues, they evidently acquire the local 11

variants and the norms of their usage too” (p. 174). Children learn to produce the acoustic and 12

articulatory goals by mainly watching, listening and imitating. Language and dialect specific 13

behavioral sources of speaker variation shape the phonemic inventory, the prosody and the 14

phonetic implementation. For example, Linker (1982) compared the lip positions in vowels 15

produced by native speakers of Cantonese and French. They found that the speakers of the 16

two languages realize different amounts of lip protrusion to make the same acoustic 17

distinction between vowels. Ladefoged (1984) points out that such language-specific behavior 18

(such as the different articulatory strategies that can be used to achieve the acoustic output of 19

/u/) is associated with group identity and a sense of belonging. Here, no physical explanation 20

based on anatomical differences between the two speaker groups is apparent. In addition to 21

language transmitting information, Ladefoged emphasizes that speech also conveys 22

sociolinguistic information and idiosyncratic characteristics of speakers. The acoustic signal 23

contains not only a lexical value, the actual meaning of the string, but also an indexical value 24

(Foulkes & Docherty 2006). These phonetic details cannot be ascribed to universal principles, 25

instead they mirror “local history and personal desire” (p. 85). Thus, the impact of non-26

biological influences such as individual language experiences and social-environmental 27

influences are both relevant to explaining inter-speaker variability. 28


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However, biological determinants must not be overlooked. While biological 1

determinants comprise brain-based (Golestani et al. 2011) and anatomical factors (e.g., 2

Vorperian & Kent 2007) we will be focusing on the latter in this study. Physiological and 3

biomechanical parameters such as larynx morphology, vocal tract geometry, palatal shape, 4

and tongue muscles directly affect the speech production process and the speaker-specific 5

strategy used in sound production. A number of studies have focused on the impact of 6

individual vocal tract properties on inter-speaker variability (Brunner et al. 2009, Fuchs et al. 7

2008, Winkler et al. 2006). Brunner et al. (2009) showed that the shape of the palate in the 8

coronal plane (palatal doming), is crucial for the degree of articulatory token-to-token 9

variability found in vowel production. Articulatory and acoustic variability was investigated 10

in 32 German speakers by means of EPG and acoustic recordings. The results showed less 11

articulatory variability in speakers with flat palates in comparison to speakers with domed 12

palates. The authors proposed that speakers with a flat palate are more constrained in their 13

articulatory variability than speakers with a dome-shaped palate, since small variations in 14

tongue position have a larger impact on the area function and hence on the acoustics. 15

Speakers with a dome-shaped palate did not show a congruent pattern in articulatory 16

variability, leaving the authors to conclude that they “have a greater range of possible levels 17

of variation since the articulatory variability they can allow for without changing the acoustic 18

output considerably is higher” (p. 3941). Other studies of inter-speaker variability in vowels 19

have dealt with the possible relationship between speaker-specific vocal tract geometries and 20

their articulatory vowel space (Winkler et al. 2006, Fuchs et al. 2008). The authors 21

investigated the articulatory distances between the corner vowels in 9 French speakers by 22

means of magnetic resonance imaging (MRI) relative to the length of the speakers’ pharynx. 23

Results indicate that speakers with a longer pharynx have larger degrees of freedom in the 24

vertical direction and produce larger displacements between low back and high front vowels 25

than speakers with a shorter pharynx. Vocal tract properties therefore constrain speech motor 26

control; they shape the degrees of freedom of articulatory behavior depending on the speaker-27

specific morphology and the relevant sound production. 28


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A recently conducted study by Rudy & Yunusova (in press) on 21 speakers of 1

Canadian English investigated the potential relationship between articulatory variability in the 2

tongue position of several consonants (including stops, fricatives and affricates) and 3

parameters associated with palatal morphology. Results revealed a correlation between 4

articulatory variability of the front consonants and palatal curvature and length. 5

The properties of the vocal tract do not only limit articulatory behavior, they also 6

make certain sounds possible. Stone (1991) proposed that the position of the tongue for 7

alveolar fricatives could not be realized by a free-standing position without the palate as a 8

reference. She suggested that the palate can be used to provide tactile feedback information in 9

order to learn and/or control specific tongue shapes. The role of tactile feedback information 10

for the production of sibilants has later been confirmed by several perturbation studies (e.g., 11

Honda et al. 2002, Brunner 2009). 12

Exploring how articulatory inter-speaker variability is influenced by the palatal shape 13

is the central issue of this study. Recently, the focus of studies on inter-speaker variability has 14

moved from the investigation of phonemic targets to the investigation of phonemic contrasts. 15

Speaker-specific behavior is often considered in the theoretical framework that focuses on the 16

link between speech production and perception. Some of the most important work that has 17

been carried out in recent years is by Perkell and colleagues (Perkell et al. 2004; Perkell 18

2010). These authors found that speakers with a lower auditory acuity of a phonemic contrast 19

also tend to produce this contrast less distinctively in comparison to speakers with a higher 20

perceptual acuity. Ghosh et al. (2010) extended this work and measured speakers’ 21

somatosensory acuity in addition to perceptual acuity and acoustic distance for the /s/-/ʃ/ 22

contrast. Somatosensory feedback involves the sensation of touch, proprioception, pain and 23

temperature. For speech production, the sensation of touch (tactile feedback) is crucial, in 24

particular for sound production with tongue-palatal contacts. Tactile feedback information is 25

transmitted via mechanoreceptors located in the tongue and the palate. In the study of Ghosh 26

et al. (2010) somatosensory acuity was obtained by pressing plastic domes with grooves of 27

different spacing against the subjects’ tongue. Subjects were asked to identify the features of 28

the grooves. Auditory acuity of the subjects was obtained by analyzing their results of an 29


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auditory discrimination task. They reported a positive correlation between speakers’ acoustic 1

realization of the /s/-/ʃ/ contrast and their auditory and somatosensory acuities. 2

Speaker-specific behavior in the production of a phonemic contrast could also be due 3

to the fact that the vocal tract morphology shapes the realization of the contrast. Our study 4

concentrates on the possible relationship between individual palate shape and the speaker-5

specific realization of the /s/-/ʃ/ contrast. Toda (2006) reported two different strategies for the 6

production of this contrast: the tongue placement strategy and the tongue adjustment strategy. 7

In the tongue placement strategy, subjects purely retract the tongue horizontally without an 8

elevation. In the tongue adjustment strategy, the tongue is elevated and follows the palate 9

contour. We propose that these speaker-specific strategies are related to individual palate 10

shape. 11

Perkell et al. (2004) examined the role of palatal morphology in sibilant production. 12

They looked at the factors palatal height, length and width, but did not find any significant 13

correlations for these parameters. However, they did not consider a parameter that is crucial 14

for the production of the sibilants, i.e. the palatal steepness. To produce a /s/, the front part of 15

the tongue is situated at the dento-alveolar ridge and a high jaw position is needed. The 16

airstream is forced through a short mid-sagittal groove along the anterior tongue blade and the 17

friction noise evolves from the airstream hitting the incisors (Shadle 1991). To produce a /ʃ/, a 18

(longer) groove is formed but here too, the tongue is situated at the anterior palatal region, 19

whereby more retracted than for /s/. We propose that this tactile information 1) is affected by 20

the shape of the alveolo-palatal ridge, and 2) has an influence on the production and 21

especially the distinction of sibilants in terms of their articulatory position. For speakers with 22

a small palatal inclination angle from the alveolar ridge to the highest point, a simple 23

horizontal retraction of the tongue tip from /s/ to /ʃ/ would already result in an appropriate 24

production, since the tongue touches the palate at the lateral margins. In contrast, speakers 25

with a relatively high and domed palate and a steep inclination angle also need to elevate their 26

tongue vertically in order to produce tongue grooving for the relevant constriction for /ʃ/. 27

Thus, these speaker-specific realizations should result in different amounts of horizontal and 28

vertical displacement between the two sibilant productions. In other words, a speaker with a 29


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flat palate should show only horizontal variation, whereas the relation between horizontal and 1

vertical displacement for speakers with higher and steeper palates should be uniformly 2

distributed (around 50% each) or even reveal a higher percentage in the vertical dimension. 3

The purpose of the present study is to test this proposition and explore speaker-4

specific strategies in the production of the phoneme contrast between /s/ and /ʃ/ in German. 5

Thus, the study aims to investigate the influence of biological determinants (parameters of the 6

palate shape, and especially the alveolo-palatal ridge) on articulatory inter-speaker variation in 7

speech production (i.e., articulatory kinematics). In Experiment 1 we will focus on articulatory 8

data of monozygotic twins (hereafter MZ) and dizygotic twins (hereafter DZ), where the latter 9

differ from the former only in the degree of genetic similarity and hence, in vocal tract 10

morphology. In Experiment 2 a more heterogeneous sample of unrelated speakers will be 11

considered. 12

We hypothesize that if high inter-speaker variability within the MZ twin pairs is found, 13

the influence of biological determinants should be negligible. If on the other hand, MZ twins 14

are more similar than DZ twins and unrelated speakers, biological determinants count. To 15

parameterize the similarity in palatal shape, several measurements are conducted. Since we 16

hypothesize the palatal steepness to be the most important factor with respect to articulatory 17

kinematics in sibilants two parameters were included: a) the inclination angle of the overall 18

palatal rise and b) the inclination angle of the alveolo-palatal ridge. The relationship between 19

these physiological parameters and the articulatory realization of the phoneme contrast in terms 20

of horizontal and vertical tongue tip displacement is then studied and discussed. 21

22

II. EXPERIMENT 1: Twin design 23

A. INTRODUCTION 24

The first experiment deals with a subject group which is rather special but particularly 25

interesting in giving remarkable insights into reasons accounting for individual variability: 26

twins. Since not every reader might be familiar with twin studies, this section focuses on the 27

background of the twin design. Especially with respect to the question of genetically or 28

environmentally caused variation between individuals, this subject group comes to the fore. In 29


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psychology, the use of twins as subjects – what is now called Twin Design (Spinath 2005) – 1

has a long tradition and goes back to the late 19th

century (Galton 1876). Within these Twin 2

Design studies the systematic comparison of the within-pair similarity between monozygotic 3

and dizygotic twin pairs is crucial. Monozygotic twins are always same-sex siblings and share 4

100 % of their genes; therefore, they are also called identical twins. Dizygotic twins only 5

share on average 50 % of their genes - like normal siblings - and can be of different sexes. 6

Genetic similarity implies anatomical and physiological similarity, if no essential surgical 7

interventions have taken place and other external factors that might influence the anatomy and 8

physiology of a person are kept constant. These external factors can be accidents but also 9

habits like drug abuse and, of particular relevance to speech production, the extensive use of a 10

pacifier that affects the palatal shape during maturation. However, if these external factors can 11

be excluded, several medical and dental studies have shown that MZ twins are more similar in 12

anatomical and physiological parameters than DZ twins, and here also regarding the organs 13

relevant to the speech production process, i.e. the larynx, the jaw, the teeth, and the palate 14

(e.g. Lundström 1948, Langer et al. 1999, Kabban et al. 2001, Eguchi et al. 2004). For the 15

production of sibilants especially the upper and lower jaw and the teeth have been shown to 16

be crucial factors (Shadle 1991, Brunner et al. 2011). The early medical investigation by 17

Lundström (1948) revealed that MZ twin pairs show less variation in size and position of jaw 18

and teeth than DZ twins. A high genetic component in dental traits was also found by Kabban 19

et al. (2001). They investigated tooth size dimensions in 34 MZ and DZ twin pairs and 20

analyzed the variation within the twin groups and between unrelated controls. In general, 21

greater similarity was apparent in twins than in the unrelated control group. In addition, the 22

remarkable similarity of MZ twin pairs (in contrast to DZ pairs) lead the authors to suggest a 23

strong inheritability of tooth size and shape that could even serve as an additional zygosity 24

determination tool. Eguchi et al. (2004) showed in their comprehensive study of 78 MZ and 25

DZ twin pairs that not only dental arch width and length but also palatal height are strongly 26

genetically determined. Thus, MZ twins, a subject group which reveals the least possible 27

variation in physiological parameters, are perfectly suited to investigate the influence of 28

morphological parameters on inter-speaker variability in speech. 29


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Of course, environmental factors also influence individual differences. Both twin types 1

are comparable in terms of shared environment during the speech acquisition process and 2

social factors influencing the speech of an individual. The Equal Environment Assumption 3

(EEA) has been investigated intensively and studies of DZ twins that grew up as MZ twins, 4

and MZ twins that grew up as DZ twins have supported the validity of this assumption (Scarr 5

& Carter-Saltzman 1979). Therefore, by investigating MZ and DZ twins, individual 6

variability can be highlighted in terms of genetically and environmentally caused factors. By 7

comparing the within-pair similarity between MZ and DZ twins (that have grown up together 8

and shared their speech acquisition process, and with a history that is not significant for 9

differences in external factors), the role of biological determinants (genes) – more specifically 10

inherent/inherited morphological parameters – can be analyzed. 11

While twin studies in the field of speech acquisition and speech pathology are quite 12

common (Locke & Mather 1989, Simberg et al. 2009, Ooki 2005), they have not been 13

conducted that often to examine inter-speaker variability in normal speech. Nevertheless, 14

some perceptual and acoustic studies have been done and they revealed that MZ twins are 15

more similar than DZ twins in mean fundamental frequency, voice quality parameters and 16

coarticulatory patterns (Przybyla et al. 1992, Debruyne et al. 2002, van Lierde et al. 2005, 17

Nolan & Oh 1996, Whiteside & Rixon 2003, Weirich 2012). Perception tests have shown that 18

it is very difficult for unfamiliar listeners to distinguish MZ and DZ twins by listening to just 19

one bi-syllabic word, while they succeed in distinguishing same-sex and age-matched 20

unrelated speakers (Weirich & Lancia 2011). Familiar listeners, however, have been shown to 21

differentiate between MZ twins (Whiteside & Rixon 2000), and also acoustic analysis of 22

formant patterns has revealed their potential to distinguish between MZ twins (Loakes 2006). 23

However, articulatory analysis of twins’ speech has not been in the focus of studies on inter-24

speaker variability, except for one study by Weirich (2012) on acoustic and articulatory 25

recording in MZ and DZ twins. This might be due to the fact that the subject group in 26

articulatory recordings is normally fairly small and by investigating twins, i.e. pairs of 27

subjects, the goal of reaching a suitable number of participants is even more difficult. 28

However, twin design studies can still be useful in giving insights into reasons for speaker-29


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specific variability. It is acknowledged that small subject samples cannot offer a complete 1

and generalizable account of the effect of physiology on speech. Still, the results can provide 2

a stepping stone for future investigations. Weirich (2012) found in her analysis of seven MZ 3

and DZ pairs no difference in the amount of within-pair similarity between the twin types in 4

the acoustics and articulation of the stressed corner vowels /a/, /i/, and /u/, while inter-speaker 5

variability in stops and sibilants tend to vary between MZ and DZ twins. Therefore, the focus 6

of the first experiment on the articulatory realization of the phoneme contrast /s/ and /ʃ/ in MZ 7

and DZ twins is to investigate the potential influence of morphological parameters such as 8

palate shape on inter-speaker variability. 9

10

B. METHOD 11

The data presented here is part of a larger project on the influence of physiological versus 12

environmental factors on articulatory and acoustic inter-speaker variability in speech (Weirich 13

2012). Here, we will focus on the production of the sibilant contrast in terms of target tongue tip 14

positions - recorded by means of an electromagnetic articulograph (EMA) - in speaker pairs 15

with an identical physiology (MZ) in comparison to the ones who also have a shared 16

environment, but different physiology (DZ). Articulatory positions will be analyzed with 17

respect to morphological parameters of the palatal shape to investigate a possible relationship 18

between the two. 19

1. Subjects and speech material 20

Altogether, six twin pairs (4 female and 2 male pairs = 12 subjects) aged between 20 and 34 21

years were investigated (participant height and weight is provided in Table 1). The genetic 22

similarity (zygosity) of the twin pairs was determined by a genetic laboratory. Four pairs (two 23

male pairs and two female pairs) were genetically identical (or monozygotic = MZ), and two 24

pairs (both female) were genetically non-identical (or dizygotic = DZ). Participants were 25

given a questionnaire to verify the extent to which they shared the same social environment 26

during speech acquisition. The questionnaire gathered information on hobbies and friends 27

they share, the time they spent together when they were young and the time they are still 28

spending together today, and confirmed that all of the twin pairs grew up together within the 29


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same social environment and lived together with their families at least until they were 18 1

years old. No considerable differences with respect to shared environmental parameters were 2

apparent between our twin pairs. The attitude they have towards being a twin was also 3

gathered and all twins revealed a very positive feeling about being a twin (for details see 4

Weirich 2012). 5

The investigated speech material contains the sibilants /s/ and /ʃ/ that occurred in the 6

target words /kʏsə/ (1. p. sg. of ‘to kiss’) and /vaʃə/ (1. p. sg. of ‘to wash’) and were part of the 7

carrier sentence “Ich wasche/küsse Hagi/a/u im Garten”. The number of repetitions of /s/ and /ʃ/ 8

differs slightly between speakers; on average 32 repetitions (SD = 4.9) for each phoneme were 9

examined. 10

11

2. Morphological measurements 12

2.1. Palatal measurements from silicone casts 13

For MZ twin pairs it is assumed that the physiological and biomechanical properties of the 14

vocal apparatus are rather similar. Since dentition and especially the incisors influence the 15

production of sibilants we made sure that the subjects still had their full set of teeth and checked 16

for braces or dental prostheses. In addition, silicone dental and palate casts (that were negative 17

imprints of the palates) were taken to examine the steepness of the alveolar ridge and the palate 18

shape more closely (cf. Figure 1). 19

20

------------ Insert Figure 1 around here --------------------- 21

22

Several measurements were conducted with the help of the cast. The maximal palatal height 23

was measured as the distance between the base and the highest point of the palate, the width of 24

the palate was measured as the distance between the 2nd molars, and the length of the palate 25

was measured mid-sagitally from the position of the 2nd molars to the highest point of the hard 26

palate before it begins declining again (see Figure 1). 27

28


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2.2. Palatal measurements from EMA recording 1

Since the quality of the palatal casts turned out to be only moderate in some cases, we also 2

measured the palatal height by means of the palatal contour recorded at the end of each EMA-3

session. The palatal contour was traced with a sensor on the experimenter’s finger. This 4

parameter is also used for further statistical analyses. For the EMA recording and in order to get 5

comparable articulatory data for the speakers of the same pair, special emphasis was laid on the 6

attempt to glue the three tongue coils at the same positions within the pairs. It turned out to be 7

more difficult to obtain the same coil positions for DZ than for MZ twin pairs, since the DZ 8

pairs differed more in tongue size. To objectify this, the distances between the three tongue 9

coils were measured, too. 10

The steepness of the palate was parameterized by calculating the angles between a 11

horizontal line through the minimal vertical position of the palate and the palatal ridge (see 12

Figure 2, plot A on the lefthand side). Two angles were measured: first, the angle defined by the 13

line between the minimal vertical point of the palate directly after the upper incisors and the 14

maximal vertical point of the palate (see Figure 2A). This angle will be called δ and 15

characterizes the general steepness of the palate. Second, the angle that characterizes the 16

steepness of the alveolar ridge was calculated (see Figure 2B). To do this, a point on the palatal 17

contour that defines the position of an alveolar step in the palatal shape was visually determined 18

(c.f. the arrow in Figure 2B). This angle will be called γ. 19

------------- Insert Figure 2 around here ---------------------- 20

21

The formula to calculate the two angles δ and γ is expressed in (1): 22

tan (δ, γ) = y(P)/x(P) (1) 23

where P is the point on the palate that determines the height y and the length x necessary to 24

calculate the particular angle. 25

26

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3. Articulatory measurement using EMA 1

EMA-recordings were conducted at the phonetic laboratory at ZAS in Berlin. Altogether, six 2

coils were attached to the tongue, the lips and the lower jaw. Two coils, one above the upper 3

incisors and one at the bridge of the nose, served as reference coils. These sensors were used to 4

compensate for head movements. The horizontal direction of each speaker’s bite plane was 5

measured by means of a custom made t-bar with two sensors attached in the anterior – 6

posterior direction. The articulatory target positions of /s/ and /ʃ/ were determined using the 7

tangential velocity of the tongue tip sensor. Furthermore, the inter-speaker variability in 8

realizing this phonemic contrast in terms of the horizontal and vertical position of the tongue tip 9

was analyzed. In doing so, we follow the idea of Toda (2006), who proposed two different 10

strategies (i.e. tongue placement and tongue adjustment strategy, which differ in the amount of 11

vertical tongue elevation - see above). Figure 3 shows the mean tongue position of /s/ (dashed 12

line) and /ʃ/ (solid line) for one speaker of MZf1 (A) and one speaker of MZf2 (B). The tongue 13

contour is interpolated over the measured positions for the tongue tip, the tongue dorsum and 14

the tongue back coil. While the speaker in plot A varies only in the horizontal position of the 15

tongue tip, the speaker in plot B differs in the horizontal and vertical position between the two 16

sound realizations. The amount of horizontal and vertical variation of the mean tongue tip 17

position between the two sounds was measured for each speaker and expressed in relation to 18

each other. This was done by summing the amount of horizontal and vertical distance and 19

setting this total amount to 100%. Then, the horizontal and vertical distance was expressed in 20

percent, too, in relation to the total amount. In addition to the mean tongue tip position, the 21

distance of the tongue tip (horizontal and vertical, in %) between all /s/- and /ʃ/- productions 22

was calculated for each speaker and used as input for t-tests conducted for each twin pair 23

(Welch two sample t-tests). We hypothesize that if the /s/-/ʃ/ contrast is influenced by 24

morphological and biomechanical factors, then MZ twins should realize it in a similar way, 25

whereas DZ twin pairs should vary to a larger extent. 26

--------------------- Insert Figure 3 around here --------------------- 27

28


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C. RESULTS 1


Table 1 summarizes the morphological parameters by showing the differences within all pairs 3

regarding body, palate and tongue measurements. It is apparent that the DZ pairs reveal the 4

greatest differences in all parameters except for one (the distance between coil 1 and 2). These 5

results support the assumption that DZ twins differ more than MZ pairs not only in general 6

properties like height and weight but also in characteristics related to the vocal apparatus, i.e. 7

tongue size and palatal shape. 8

9

------------- Insert Table 1 around here ------------------ 10

11

2. Articulatory measurements 12

To quantify the difference in how the speakers realize the /s/-/ʃ/ contrast, the horizontal and 13

vertical distance between the realizations of the two sibilants was calculated as described 14

above (c.f. Figure 3). Then the distances were expressed in percent to emphasize the relation 15

between the horizontal and the vertical variation, and to normalize for potential differences in 16

overall vocal tract size between subjects. Figure 4 displays the horizontal variation of the 17

tongue tip between the two sibilants (in percent) for all repetitions and each speaker 18

separately. Speakers of the same pair are plotted next to each other. The highest differences 19

reveal the two DZ pairs. The speakers differ in their mean value of horizontal variation for 20

about 14% (DZf1) and 20% (DZf2). Within the MZ pairs, MZm1 differs most (for about 21

10%). Welch two sample t-tests were conducted for each twin pair and as apparent in the 22

figure both DZ pairs show significant differences (p < 0.01) while none of the MZ pairs does. 23

24

--------------------------------- Insert Figure 4 around here ---------------- 25

26

3. Relation between morphology and articulation 27

In a next step, the relation between several morphological parameters and the articulatory 28

realization of the phoneme contrast was analyzed. Note that the parameter used to express the 29


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articulatory realization was the horizontal tongue tip displacement. Since this displacement 1

was expressed in percent, both the horizontal and vertical distance between the sibilant 2

productions are captured by this parameter. 3

First, the relation between palatal height and horizontal tongue movement was 4

investigated. Nonparametric Spearman’s rho ranked correlations were negative but failed to 5

show significance (rho = -0.32, p-value = 0.15). 6

The most interesting parameter seems to be the steepness of the palate, since it better 7

describes the specific characteristic of the relevant morphological boundaries influencing the 8

articulatory strategy. Figure 5 shows the relationship between the palatal steepness (x-axis), 9

which is expressed in the angle δ as described above, (c.f. Figure 2, Part A) and the mean 10

horizontal distance of the tongue tip between the two sibilants (in percent, y-axis). The MZ 11

twin pairs are marked with filled shapes, the two DZ twin pairs using a cross and an unfilled 12

square. Speakers coming from the same twin pair have the same markers. It is apparent that 13

the markers of all MZ twin pairs lie next to each other both in terms of articulatory distance 14

and the morphological parameter palatal steepness. In contrast, the markers of the DZ pairs 15

differ between the twins in both factors. The two parameters are significantly correlated, and 16

the relationship is much stronger than it was for the palatal height (Spearman rank-order 17

correlations: rho = - 0.53, p < 0.05). The smaller the angle (the flatter the inclination of the 18

palate), the greater is the percentage of horizontal distance between the realizations of the two 19

sibilants. 20

21

---------------------------- Insert Figure 5 around here ------------------------- 22

23

In Figure 5 one outlier is apparent. One speaker of DZf1 reveals a high angle δ (39.1°) and 24

thus a steep rise of the hard palate but also substantial horizontal difference between the two 25

sibilants (85.7 %). As described above, a second angle γ that characterizes the steepness of 26

the alveolo-palatal region (c.f. Figure 2, Part B) was calculated. Figure 6 displays the 27

relationship between γ and the percentage of horizontal distance of the tongue tip between the 28

sibilants for all speakers. The relation between the articulatory strategy and this angle is even 29


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stronger than the one reported above. The angle γ of the speaker of DZf1 is smaller than the 1

angle δ and thus the alveolo-palatal region is much less steep than the general palatal rise. In 2

addition to the calculated alveolo-palatal angles of the other speakers this results in a stronger 3

correlation than reported for the general palatal angle δ (rho = -0.78, p < 0.01). Thus, 4

compared to palatal height and the overall palatal steepness, the alveolo-palatal region is the 5

most important investigated morphological parameter that influences the strategy used to 6

produce the sibilant contrast in terms of the relation between horizontal and vertical distance. 7

8

------ Insert Figure 6 around here ----------- 9

10

In summary, results from our twin study show: 1) a consistent articulatory behavior regarding 11

the vertical and horizontal relative distances in the realization of the /s/-/ʃ/ contrast for 12

genetically identical twins, whereas such consistent behavior was not found for non-identical 13

twins; and 2) an impact of morphological parameters on these distances: the steeper the 14

palate, the less horizontal (and the more vertical) distance in the realization of the contrast is 15

apparent. Overall, the morphology of the alveolo-palatal region, where the contrast is 16

produced, turned out to be the strongest influencing factor. 17

These results support the idea that palatal morphology is a crucial constraint in shaping 18

the production of the /s/-/ʃ/ contrast. However, the subject group under investigation is 19

homogeneous and special with regard to physiological similarities. In addition, 2D EMA 20

recordings can give us information about the mid-sagittal area of the tongue, while the sides 21

of the tongue touching the palate to build an air channel crucial for sibilants cannot be 22

analyzed. Therefore, a second experiment conducted by means of electropalatography is 23

described below. Here, the relation between morphology and the production strategies of the 24

two sibilants was examined in unrelated speakers. The palatal casts used during EPG are 25

individually designed for each speaker and give us additional information on the palatal 26

morphology. 27

28

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III. EXPERIMENT 2: Unrelated speakers 1

2

A. INTRODUCTION 3

The aim of the second experiment was to investigate the individual /s/-/ʃ/ contrast in a more 4

heterogeneous group of speakers in order to allow for general conclusions and relate their 5

production of the contrast to various morphological parameters of the palate (e. g. palatal width, 6

length, height, doming and steepness). 7

8

B. METHOD 9

1. Subjects and speech material 10

12 German speakers (five male and seven female speakers, aged 24-56) were recorded by 11

means of electropalatography (Reading system, EPG3). Subjects reported no speech, language 12

or hearing deficits and had a normal Body Mass Index between 19 and 25. All of them were 13

academics. The choice of the subjects was based on the availability of a custom-made EPG 14

palate. Subjects produced /s/ and /ʃ/ in the nonsense target words /zasa/ and /ʃaʃa/ approximately 15

30 times each. The target words were embedded in a carrier sentence and presented randomly; 16

they are part of a much larger database reported in Brunner et al. (2005). We focused only on /s/ 17

and /ʃ/ in word medial position, since in contrast to the word initial position it is not confounded 18

by voicing contrast (in word initial position the alveolar fricative is phonologically voiced and 19

has no voiceless counterpart in native German vocabulary). 20

21


Morphological parameters of the custom made EPG palates were measured on the basis of the 23

x, y and z coordinates of the 62 electrodes embedded in the artificial palate. 24

25

------------------ Insert Figure 7 around here ------------ 26

27

Since in the Reading EPG system the electrodes in the artificial palate are placed with respect 28

to anatomical landmarks based on a dental cast (Hardcastle, Gibbon & Jones 1991), it allows 29


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us to observe aspects of speaker-specific palatal morphology. In order to do so, each palate 1

was fitted to its dental cast and a high quality 1:1 photo-copy was made for each speaker. This 2

copy served as a reference to measure the horizontal (x) and vertical (y) coordinates of each 3

of the 62 electrodes by means of a Vernier caliper (see Figure 7). To measure the height of 4

each electrode in the artificial palate, the EPG palate was attached to the individuals’ dental 5

cast. In the following step a plastic plate of 7 mm thickness and a small hole in the middle 6

was put on top of the dental cast. By means of the Vernier caliper a depth probe was obtained 7

via the hole in the plastic plate for each electrode. 8

The horizontal distance between the two most peripheral electrodes in the first 9

(anterior) row in the palate was defined as anterior palatal width (width_ant). Similarly, the 10

horizontal distance between the two most peripheral electrodes in the last row was defined as 11

the posterior palatal width (width_post). Since palates can be slightly asymmetric, the length 12

of the palate (length) was calculated as an average of the two distances from the most anterior 13

and to the most posterior electrodes on the left and right side of the palate (see Figure 7). 14

To estimate the palatal doming for each electrode row (alpha2, … , alpha8) we used 15

the method proposed by Brunner et al. (2009). A parabolic approximation was calculated on 16

the x- (palatal width) and z-data (palatal height) of each electrode row (alpha2 corresponds to 17

the doming in the second row, alpha3 to the third row and so on). Alpha 1 was not included in 18

the analysis, since it is based only on the values of six electrodes and in most cases it is 19

completely flat. Note that, lower alpha values reflect more domed palate shapes in 20

comparison to higher alpha values. 21

Additionally, we calculated the two angles, δ and γ, as in Experiment 1. In the EPG 22

palate the mid-sagittal plane lies between the electrodes of the 4th

and 5th

column. To define 23

the mid-sagittal plane we therefore averaged the y- (palatal length) and z-data (palatal height) 24

of the 4th

and 5th

column for each row. An example is given in Figure 8. 25

26

------------ Insert Figure 8 around here -------- 27

28

29


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3. Articulatory measurements using EPG 1

Electropalatographic recordings were carried out in Experiment 2. In contrast to the articulatory 2

recordings in the mid-sagittal plane (Experiment 1), they allow us to obtain insights into the 3

articulatory behaviour at the sides of the tongue. Lateral contacts of the tongue at the palate are 4

crucial in the production of sibilants, since they are required for building a channel which 5

directs the air stream towards the incisors (Shadle 1991). 6

Based on electropalatographic data it is impossible to define the vertical and horizontal 7

movement of the tongue as it was carried out in Experiment 1. An alternative is to define 8

place of articulation reflecting the placement of the tongue in the horizontal direction and the 9

respective differences between phonemes. Therefore, places of articulation for /s/ and /ʃ/ were 10

defined using the articulatory Centre of Gravity (COG) measure (Hardcastle, Gibbon & 11

Nicolaidis 1991). It is a weighted index, adding successively more weight to rows which are 12

more front than back, i.e., a high COG index reflects a more anterior place of articulation than 13

a low COG. As a distance measure we calculated the difference in COG between /s/ and /ʃ/ 14

(Cog_diff). COG values for all repetitions of each speaker’s phoneme production were 15

averaged for further statistical analyses. 16

17

C. RESULTS 18

Spearman rho ranked correlations were calculated with COG_diff and one of the palatal 19

parameters. Since our sample size is limited (n=12), the likelihood of getting significant 20

correlations is rather small and the influence of extreme points increases. Table 2 provides an 21

overview of the relation between parameters of the palate shape and the contrast realization in 22

place of articulation. 23

24

---------------- Insert Table 2 around here ---------------- 25

26

Table 2 shows a significant negative correlation between differences in place of articulation 27

between the sibilants and the angle of the alveolo-palatal ridge (γ), the less steep the palate in 28

the anterior region, the greater the horizontal distance in place of articulation between /s/ and 29


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/ʃ/ (rho = -0.615, p = 0.0373). The relation between the two parameters is shown in Figure 9. 1

It is similar to the results of Experiment 1. In Figure 9 results are displayed according to 2

gender to account for a potential bias that males have a larger difference in place of 3

articulation than females (see Fuchs & Toda 2010). However, here, no systematic difference 4

is visible between males and females, which may be attributed to the relatively small sample. 5

6

------------ Insert Figure 9 around here ---------------- 7

8

One data point in Cog_diff is extremely high. This male speaker realizes the postalveolar 9

fricative very far back. If the extreme point is removed from the analysis, the correlation 10

between the angle of the alveolo-palatal ridge (γ) and Cog_diff becomes even stronger (rho = 11

-0.664, p < 0.03). Moreover, the correlation of Cog_diff with alpha2 almost reaches 12

significance (rho = 0.583, p-value = 0.059). Alpha2 corresponds to the part of the alveolar 13

ridge where /s/ is commonly realized in German. It is usually characterized by a small step 14

which can be very different among speakers be more or less prominent. 15

In contrast to Experiment 1, the correlation between the horizontal distance in place of 16

articulation between the sibilants and the angle of palatal steepness (δ) did not reach 17

significance. A possible reason might be that our sample did not differ considerably in palatal 18

steepness (range: 26.5°-39°). 19

20

IV. DISCUSSION AND CONCLUSION 21

22

Our work investigated inter-speaker variability in the realization of the sibilant contrast in 23

German and how it is affected by biological determinants, e.g., the shape of the palate. In 24

Experiment 1, a twin design study was used to ensure control for non-biological determinants, 25

such as social and environmental factors that have been shown to have a strong impact on 26

speech production (Labov 1994, Faulkes & Docherty 2006). By examining inter-speaker 27

variability in MZ and DZ twins, variability can be analyzed in terms of biological and non-28

biological determinants (Spinath 2005, Scarr & Carter-Saltzman 1979). The subjects for 29


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Experiment 1 were chosen in a way that the twin types did not differ substantially with 1

respect to social environmental factors. By controlling this factor as much as possible the 2

differences in within-pair similarity between MZ and DZ pairs can be ascribed to differences 3

in biological determinants. The results revealed that MZ twins show a greater amount of 4

articulatory similarity in the production of the sibilant contrast than DZ twins. We 5

hypothesized that this similarity is caused by the greater similarity in palatal morphology in 6

MZ than in DZ twins. Results provided evidence that speaker-specific strategies depend on 7

the steepness of the alveolo-palatal ridge and the general steepness of the palate. 8

This is mainly due to the fact that the tongue needs to follow the palate shape in order 9

to stabilize its position (Stone 1991) and to build a channel for the required air stream. Both 10

lateral margins of the tongue are in contact with the palate, and are crucial for producing the 11

articulatory constriction in the /s/-/ʃ/ contrast. Speakers with a flat inclination angle of the 12

palate (and in particular of the alveolo-palatal region) produce the contrast by retracting the 13

tongue horizontally whereas speakers with a steep palatal inclination angle not only retract, 14

but also need to elevate the tongue (i.e., show vertical tongue displacement) to maintain 15

contact with the palate and build an air channel that directs the air flow towards the incisors. 16

The speech material that was recorded by means of electropalatography served as an 17

additional source of examining inter-speaker variability in unrelated speakers in the 18

articulatory realization of the sibilant contrast in German. The analysis of a set of genetically 19

unrelated speakers confirmed the role of the alveolo-palatal steepness in the production of the 20

contrast. Other palatal parameters did not show a correlation with articulatory strategies but 21

they were generally also less variable among the subjects. An exception was the palatal 22

doming in the second row of the palate, which is located in the area where the sibilants are 23

produced and where speakers can vary in terms of a flat or steep alveolar ridge: the 24

correlation with the contrast just failed to reach significance. Our experiment was limited to 25

twelve subjects. With such a sample size, extreme points have a large effect on the 26

significance of the correlation. Nevertheless, moderate but significant correlations were found 27

and most studies reporting inter-speaker variability show in general only weak correlations 28


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(e.g. Perkell et al. 2004, Perkell 2010, Gosh et al. 2010). This might be explained by the 1

various factors influencing inter-speaker variability in general. 2

Studies dealing with inter-speaker variability in the realization of the sibilant contrast 3

have shown that somatosensory and auditory acuity plays a role (Perkell et al. 2004, Gosh et 4

al. 2010). From our results of the articulatory analysis of both the EMA and the EPG data we 5

conclude that next to speaker-specific auditory and somatosensory acuity, individual 6

morphological differences in palatal shapes influence the articulatory realization of the /s/-/ʃ/ 7

contrast in German. 8

In particular, the steepness of the alveolo-palatal ridge is crucial in determining the 9

articulatory distance (in terms of horizontal and vertical tongue tip displacement) between the 10

two sibilants. The ridge is the place where the contrast is realized, and somatosensory 11

feedback information may be available to learn the phonemic contrast or adjust tongue 12

position when external perturbations are applied (e.g. Honda et al. 2002, Brunner 2009). 13

Perkell et al. (2004) also considered the role of palatal morphology in sibilant production, and 14

focused on palatal height, length, width and mandibular width and length. In agreement with 15

our findings, they did not find any significant correlations for palate height, length and width. 16

Hence, our results are in general agreement with their work, but allow different conclusions, 17

since we additionally investigated the steepness of the alveolo-palatal ridge and found a 18

correlation for realization of the sibilant contrast. This parameter provides a less general 19

description of the palate shape, and is more specific to the place where the two sibilants are 20

realized. 21

A future investigation, combining a number of phonemic contrasts, may reveal 22

whether individual somatosensory acuity might actually be linked to individual palate shape, 23

i.e., the location where the tongue touches the palate quite frequently during speech 24

production. We would predict that speakers with a large amount of tongue-palatal contact 25

(speakers with a flat palate) show a higher somatosensory acuity in comparison to speakers 26

with a domed palate. This may in turn go hand in hand with the speakers’ perceptual 27

discriminability of the phonemic contrast, since speakers with a certain palatal shape need to 28


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learn a certain articulatory precision for the realization of a contrast, and in parallel also tune 1

their perception system to differentiate between the phonemes. 2

From this perspective, individual morphological parameters and the maneuvers of the 3

tongue at the vocal tract boundaries may determine to some extent the development of 4

somatosensory acuity. What speaks in favor of a potential relationship between the 5

distribution of somatosensory feedback and vocal tract morphology is the fact that most 6

mechanoreceptors that can sense the information of touch are situated in the tongue tip and 7

blade but less in the tongue back (see e.g. Hardcastle 1971). The former areas of the tongue 8

may be more frequently used in consonant production than the latter, since various languages 9

have a high density of coronal sounds in their phoneme inventory. First experimental 10

evidence for such a view was provided by Ruty & Yunusova (in press) who were able to 11

show that tongue position variability was constrained by palate shape (palatal curvature and 12

length) for front consonant groups, but not for back consonants. 13

We suggest that it is important to consider morphological constraints in conjunction 14

with articulatory behavior when studying speaker-specific variability. By investigating not 15

only phonemic targets but also the articulatory strategies in realizing phonemic contrasts, the 16

importance of analyzing inter-speaker variation becomes even more apparent. In phonology 17

the place of articulation is specified rather precisely although speaker-specific variations have 18

been reported for a long time, especially considering coronals. Dart (1998) has shown that a 19

high amount of individual variation exists in the place of articulation and in the point of 20

constriction on the tongue regarding the production of coronal consonants in English and 21

French. Therefore, the place of articulation as the distinguishing parameter for coronal 22

consonants within and between languages should be considered with caution. For example, if 23

a subject realizes a /s/ rather back, e.g., at a post-alveolar place of articulation, it is very likely 24

that this subject realizes a /ʃ/ even further back. In contrast, a subject who produces a /s/ rather 25

front at a dental place of articulation may also show fronting for the production of a /ʃ/. 26

Hence, the realization of a given target should be seen relative to the production of other 27

sounds. We assume that in most cases not the exact place of articulation of a sound might be 28

the most meaningful parameter but the relation between the produced sounds within a 29


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particular phoneme inventory and thus the realization of the phoneme contrasts. The 1

individual implementation of these phonemic contrasts can help understanding speech from a 2

different perspective. This result stands in contrast to most phonological theories which 3

consider speaker-specific behavior as a source of random noise with no impact on abstract 4

phonemic categories. 5

6

Acknowledgements: 7

This work was funded by a grant from the Federal Ministry of Education and Research 8

(01UG0711). We thank Jörg Dreyer for technical expertise, Jana Brunner for providing EPG 9

data, Adrian Simpson and Blake Rodgers for proof reading, Amelie Rochet-Capellan for 10

helpful comments on an earlier version of this paper and our participants. 11

12

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Figure captions 1

Figure 1: Inferior view of silicone palatal casts taken from all female twin participants. Top 2

panel: 2 DZ pairs. Bottom panel: 2 MZ pairs. Lines indicate palatal width (posterior, 3

horizontal) and palatal length (vertical) measurements as defined in text. 4

Figure 2: Parameterization of the steepness of the palate by measuring the angle of the 5

general palatal rise (δ) (see plot A), and the angle of the alveolo-palatal ridge (γ) (see plot B, 6

close up view). The thick black line shows the palatal contour, the thinner dashed horizontal 7

lines represent the minimal and maximal vertical position of the palate. P defines the highest 8

point of the palate (in A) and the visually determined position of an alveolar step in the palatal 9

shape (in B) (c.f. the arrow in Figure 2B). x and y show the vertical and horizontal interval 10

determined by P. 11

Figure 3: Visualization of the distance measurement (in horizontal and vertical dimensions) 12

between the mean tongue tip positions of the two sibilants for two different speakers. Plot A) 13

twin 1 from MZf1, plot B) twin 1 from MZf2. Top curves show the palate contours, bottom 14

lines show the tongue outlines for /s/ (dashed line) and /ʃ/ (solid line). 15

Figure 4: Percentage of horizontal variation of the tongue tip between /s/ and /ʃ/ productions 16

for all repetitions and each speaker separately; speakers of the same pair are plotted next to 17

each other (p-values are given for significant differences); the black lines separate twin pairs 18

(DZ left, MZ right). The median of the distribution for each speaker is visualized by a black 19

dot in the boxes; the boxes comprise 50% of the data; the whiskers extend to the most 20

extreme data point which is no more than 1.5 times the interquartile range from the box; 21

outliers are marked with open dots. 22

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Figure 5: Relationship between the angle of the palatal steepness (in degree, x-axis, 1

increased angle implies increased steepness), and the horizontal distance of the tongue tip 2

between the two sibilants (in percent, y-axis). MZ speakers are marked by filled symbols, DZ 3

speakers marked by open symbols. Participant height and weight information listed in Table 4

1. 5

Figure 6: Relationship between the angle of the alveolo-palatal steepness (in degree, x-axis, 6

increased angle implies increased steepness), and the horizontal distance of the tongue tip 7

between the two sibilants (in percent, y-axis). MZ speakers are marked by filled symbols, DZ 8

speakers marked by open symbols. Participant height and weight information listed in Table 9

1. 10

Figure 7: Example of palatal parameters measured. Top image (inferior view) with x-axis 11

corresponding to palatal width and y-axis to palatal length (parameters displayed: anterior 12

width, posterior width, and palatal length). Bottom image (coronal view) with x-axis 13

corresponding to palatal width and y-axis to palatal height (parameters displayed: palatal 14

height and coronal doming). 15

Figure 8: Palatal contour in the mid-sagittal plane obtained from measures of the electrodes 16

in an EPG palate. Plot A: calculation of angle of the general palatal rise (δ), plot B: the angle 17

of the alveolo-palatal ridge (γ) (see also Figure 2 for comparison). X-axis corresponds to 18

horizontal dimension and y-axis to vertical dimension. 19

Figure 9: Relation between the angle of the alveolo-palatal ridge (in degree, x-axis, increased 20

angle implies increased steepness) and the difference in place of articulation between the 21

sibilants (expressed as COG, y-axis). 22

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Table 1: Body, palate and tongue measurements for each speaker, differences within twin 1

pairs in parentheses. Palate width measured between the 2nd molars, difference in length of 2

the hard palate measured from the midpoint of the vertical line between the 2nd molars to the 3

point at which the palate starts to descend (this point was visually determined). 4

5

Twin

pair

Body measures Palate cast measures

(in cm)

Tongue measures from

EMA (in cm)

height

(m)

weight

(kg) Heigth width length

ttip –

coil 1

coil 1 –

coil 2

coil 2 –

coil 3

MZf1

1.74

1.73

(0.01)

57

62

(5)

2.1

2.1

(0.0)

4.0

4.1

(0.1)

2.7

2.6

(0.1)

0.4

0.4

(0.0)

2.0

1.9

(0.1)

2.4

2.5

(0.1)

MZf2

1.64

1.64

(0.00)

49

46

(3)

1.8

1.8

(0.0)

3.9

4.0

(0.1)

2.8

2.6

(0.2)

0.55

0.5

(0.05)

1.6

1.7

(0.1)

1.7

2.0

(0.3)

MZm1

1.79

1.78

(0.01)

65

70

(5)

2.5

2.4

(0.1)

4.2

4.1

(0.1)

2.3

2.4

(0.1)

0.6

0.5

(0.1)

1.8

2.0

(0.2)

2.0

1.9

(0.1)

MZm2

1.72

1.72

(0.00)

63

62

(1)

2.6

2.4

(0.2)

4.4

4.3

(0.1)

2.3

2.0

(0.3)

0.6

0.65

(0.05)

2.4

2.3

(0.1)

2.0

1.9

(0.1)

DZf1

1.68

1.70

(0.02)

54

55

(1)

2.1

2.0

(0.1)

3.8

3.6

(0.2)

2.8

2.6

(0.6)

0.6

0.5

(0.1)

2.0

1.9

(0.1)

2.1

2.0

(0.1)

DZf2

1.65

1.68

(0.03)

51

63

(12)

2.2

2.5

(0.3)

3.8

3.4

(0.4)

2.5

3.0

(0.5)

0.6

0.5

(0.1)

2.0

2.0

(0.0)

1.8

2.4

(0.6)


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Table 2: Overview of spearman rho correlations with Cog_diff between /s/ and /ʃ/ and one of

the palate parameters.

COG_diff with rho p-value

width_ant -0.224 0.485

width_post -0.151 0.639

Length 0.042 0.895

Height 0 1

alpha2 0.511 0.089

alpha3 0.007 0.982

alpha4 0.1611 0.617

alpha5 -0.287 0.365

alpha6 -0.385 0.216

alpha7 -0.441 0.1509

alpha8 -0.371 0.2347

angle δ -0.161 0.6194

angle γ* -0.615 0.0373

1

2


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Figure 1 1

2

3

4

5

6

7

8

DZf1 DZf2

MZf2 MZf1

DZf1 DZf2

MZf2 MZf1

width

len

gth


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Figure 2 1

2

3

4

5

6

7

8

9


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Figure 3 1

2

3

4

5

6

7

8


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Figure 4 1

2

3

4

5

6

7

twin participants

horizontal ttip variation (in %

)

20

40

60

80

100

DZf1a DZf1b DZf2a DZf2b MZf1a MZf1b MZf2a MZf2b MZm1a MZm1b MZm2a MZm2b

p < .01 p < .01


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Figure 5 1

2

3

4

5

6

7

8

9

10

20

30

40

50

60

70

80

90

100

20 30 40 50

MZf1

MZf2

MZm1

MZm2

DZf2

DZf1

Horizontal distance of ttip

between sibilants (%)

Angle of palatal steepness (°)


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Figure 6 1

2

3

4

5

6

7

8

9

10

20

30

40

50

60

70

80

90

100

10 20 30 40 50

MZf1

MZf2

MZm1

MZm2

DZf2

DZf1

Horizontal distance of ttip

between sibilants (%)

Angle of alveo-palatal ridge (°)


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Figure 7: 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

Width_ant

Width_post

Length

y-coordinate

x-coordinate

z-coordinate

Doming

Height


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Figure 8 1

2

3

4

5

6

7

8

9

10

11


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Figure 9 1

0.00

0.50

1.00

1.50

2.00

2.50

3.00

0 10 20 30 40 50

Difference in articulatory COG

Angle of alveolo-palatal ridge (°)

Female

Male


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Palatal morphology influences the production of phonemic contrasts (like s-sh)

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Transcript of Palatal morphology influences the production of phonemic contrasts (like s-sh)