1.1. Articulation of geminates

Phonological quantity contrast used in many languages is phonetically realized mostly by differences in acoustic duration of vowels or consonants.

Investigators comparing articulatory patterns associated with the production of phonologically short and long segments report several regularities in kinematic characteristics reflecting this primary phonetic cue. Yet, it should be noted that previous studies use different measurement procedures and linguistic material which can be the cause of variability in the findings. This might suggest that the phonological contrast is not clearly manifested in articulatory patterns across various contexts. Therefore, our study has partly been inspired by these differences.

Studies focused on consonantal gemination show significantly longer durations of articulatory closure for geminates compared to singletons (e.g., Löfqvist, 2006, 2007 for Japanese stops, sonorants, and fricatives; Bouarourou et al., 2008 for Tarifit Berber stops and fricatives; Ridouane, 2007 for Tashlhiyt Berber stops; Zeroual et al., 2008 for Moroccan Arabic stops). The movements of relevant articulators to and from the constriction targets for geminates have longer durations than for singletons (Fivela et al., 2007 for Italian stops and sonorants; Zeroual et al., 2008 for Moroccan Arabic stops; Šimko et al., 2014 for Finnish stops). Also, quantity influences spatial extent of articulatory movements in the expected direction. Larger lip closing and opening movements were found for geminate bilabials compared to their singleton counterparts for example for Italian and Japanese stops and sonorants and for Finnish stops (Fivela & Zmarich, 2005; Löfqvist, 2005; O’Dell et al., 2011). Velocity profiles of relevant articulators exhibit more varied patterns regarding the quantity contrast. Several researchers have reported lower articulatory velocity for long segments than for short ones (e.g., Smith, 1995 and Löfqvist, 2005 for Japanese stops, sonorants, and fricatives; Šimko et al., 2014 for Finnish stop consonants), but others have found significantly higher velocity for geminates than singletons (Löfqvist, 2005 for Swedish and Bouarourou et al., 2008 for Tarifit Berber stops and fricatives). In addition, no significant effect of quantity on movement velocity was reported in several other studies (e.g., Fivela et al., 2007 for Italian stops and sonorants and Zeroual et al., 2008 for Moroccan Arabic stops).

Phonological quantity of a consonantal segment also affects kinematic properties of neighboring gestures. In particular, the duration of articulatory transition between vowels flanking a consonant tends to be longer when the consonant is geminate compared to singleton (Löfqvist, 2006 and Smith, 1995 for Japanese stops and sonorants; Šimko et al., 2014 for Finnish stops [see also an acoustic study by Lehtonen, 1970]; Fivela et al., 2007 for Italian stops and sonorants, but see also Smith, 1995 with different results). Studies offer mixed results regarding the influence of consonantal quantity on spatial extent of the inter-vocalic gesture: No effect for Japanese sonorants (Löfqvist, 2006; but generally greater extent in geminate context for stops and fricatives reported in Löfqvist, 2007) and expansion for geminates in Finnish stops (Šimko et al., 2014). These three studies also suggest slower transition gestures in geminate context.

Vowel quantity also influences kinematic characteristics of gestures participating in the vowel production. Quantity has a significant effect on the durations of the gestures from a constriction preceding and to a constriction following the vowels with shorter durations for the short vowels (Beňuš, 2011 for Slovak; Hertrich & Ackermann, 1997 and Kroos et al., 1997 for German lax/tense contrast). The peak velocity of both preceding and following gestures decreased with quantity; while for German lax/tense contrast the effect of quantity on following gestures is minimal (Hertrich & Ackermann, 1997) for Slovak short/long distinction—generally not accompanied by quality differences—the effect is reported to be greater for the following than the preceding gesture (Beňuš, 2011). The spatial extent of the flanking gestures and of the lingual gestures associated with vowel production is greater for long compared to short vowels (Beňuš, 2011). Interestingly, Hoole and Mooshammer (2002) report a greater spatial extent of the lingual gestures for tense German vowels compared to their lax cognates but only for central and back vowels; quantity does not influence the extent for more articulatorily constrained front vowels.

A consonant, singleton or geminate, is generally coproduced with a following vowel. In the literature, two accounts for coproduction have been suggested. Öhman (1966) claims that vowels are produced continuously, i.e., movements from the first vowel to the following one are produced as diphthongal and consonantal gesture is superimposed on that trajectory. Recent coproduction theory by Fowler and Saltzman (1993) proposes a view according to which vowels are produced as separate gestures and the gestures for vowels and consonants overlap temporally (see also Fowler, 1980). Using the notion of gestural activation waves, Fowler and Saltzman (1993) show how gestures are coproduced in speech—each gesture influences vocal tract shape smoothly as there are gradual implementation (anticipatory field of coarticulation) and relaxation (carryover field of coarticulation) phases during the activation of a gesture. These phases overlap with adjacent gestures, i.e., they are coproduced. The amount of overlap depends on the extent to which articulators are shared (the degree of spatial overlap). In cases where all articulators are shared, the gestures are competing for the control of articulators during periods of coproduction, which leads to a process of intergestural blending. Thus, context-sensitivity is seen as a consequence of the time courses of the activation waves of gestures and the manner of blending.

Somewhat consistently with the aforementioned theories, Smith (1995) presents two models for the temporal coordination between vowels and consonants. According to the “combined vowel-and-consonant timing” model, vowels and consonants are mutually coordinated, and thus, vowels are affected by the temporal properties of consonants. Smith (1995) showed that this is the case in Japanese (mora-timed language), where the differences in consonant duration influence the timing between the vowel gestures. The “vowel-to-vowel timing” model supports Öhman’s (1966) theory of continuous vowel production, and according to this, vowels are not affected by the properties or the number of consonants. The results of Smith’s (1995) study showed that in Italian (a syllable-timed language) the timing of tongue movements for vowels remains the same regardless of the length of an intervocalic consonant.

More precisely, the gesture associated with the consonant, e.g., lip closing gesture for a bilabial, starts around the same time as the intervocalic transition, i.e., the tongue movement towards the constellation appropriate for the vowel acoustically succeeding the consonant (see e.g., Öhman, 1966). The details of relative timing of the onsets of these two parallel gestures, however, depend on articulatory characteristics of the vowels involved in the intervocalic transition. For example, the transition movement tends to start relatively earlier with respect to the lip closing one when the transition is /ɑ-i/ as opposed to/i-ɑ/ (Löfqvist & Gracco, 1999; Šimko & Cummins, 2009, 2010). The relative timing is also influenced by the preceding consonant: The lip closure onset for a bilabial is delayed relative to the onset of intervocalic transition if the preceding consonant is a homorganic bilabial compared to a non-homorganic one, e.g., /t/ (Šimko et al., 2014; see also a discussion of gestural crowding in Beňuš & Šimko, 2014).

Directly relevant for the present study is a finding reported by Šimko et al., (2014) about an influence of gemination on the intergestural coordination. In the material investigated—Finnish stimuli /pɑCi/, /piCɑ/, /tɑCi/, and /tiCɑ/ where C is either a singleton or geminate /p/—the duration of the interval between the onsets of lip closing for C and coproduced intervocalic transition was in addition to the aformentioned contextual factors also influenced by the quantity of C. Namely, the lip closing movement started earlier relative to the lingual one when C was a geminate than when it was a singleton. Additionally, the authors report an interaction between context-sensitivity of intergestural timing and gemination in Finnish: The effect of gemination was weaker in the /i-ɑ/ than in the /ɑ-i/-context. Furthermore, in the /i-ɑ/-stimuli, the effect of gemination was still further diminished by the preceding /p/ to the extent that for several speakers the lip closing gesture actually started earlier (relative to the lingual gesture) for singletons than for geminates.

In the current paper, we will study these effects in more detail. In addition to the inter-gestural coordination, we will investigate the interaction between the context and quantity for other kinematic measures such as duration, spatial extent, and peak velocity of individual gestures. Further, in addition to consonant quantity, we include a variation in vowel quantity. Most importantly, we will study these phenomena on a three-way quantity contrast in one of the very few languages that include such a system, Estonian.

1.2. The Estonian three-way quantity

The three-way quantity is the most studied feature of Estonian word prosody, and has been investigated in numerous acoustic and perception studies (e.g., Lippus et al., 2009, 2011; Lippus et al., 2013; Lehiste, 2003; Eek & Meister, 1997, 2003). In comparison, articulatory studies of Estonian quantity are relatively rare.

In a number of studies (e.g., Lippus et al., 2013; Lehiste, 2003; Eek & Meister, 1997) it has been shown that the domain of quantity in Estonian is a left-headed (i.e., stress on the first syllable) disyllabic foot, where stressed syllables can have three degrees of quantity based on syllable length (short and long) and weight (light and heavy): A Q1 syllable is short and light, a Q2 syllable long and light, and a Q3 syllable long and heavy (Viitso, 2003, pp. 11–13). Incorporating all segmental durations within the foot, the quantity opposition between short (Q1), long (Q2), and overlong (Q3) feet is realized by the stressed-to-unstressed syllable rhyme duration ratio and some additional features (namely the pitch movement and vocalic quality). As the unstressed syllables cannot have distinctive length oppositions independent of the stressed syllables, their duration lengthens or shortens compensatorily in the opposite direction of the stressed syllable.

While on the foot level there is a three-way opposition of stressed-to-unstressed syllable length, the stressed syllable rhyme duration is achieved by combining vowel and consonant length. The three-way contrast can be accomplished by lengthening the stressed vowel, the intervocalic consonant, or both, enabling minimal septets of C1V1C2V2-sequences based on segmental duration: Q1—short V1 short C2 [sɑte] ‘fall-out, sg. nom.’ —Q2—long V1 short C2 [sɑːte] ‘broadcast, sg. nom.,’ short V1 long C2 [sɑtte] ‘fall, sg. nom,’ long V1 long C2 [sɑːtte] ‘get, pl. 2^nd pers.’—Q3—overlong V1 short C2 [sɑːːte] ‘haystack, pl. part.,’ short V1 overlong C2 [sɑtːte] ‘fall, sg. gen.,’ long V1 overlong C2 [sɑːtːte] ‘broadcast, sg. gen.’ Regardless of the segmental structure of the stressed syllable, the quantity distinction is best described by the duration ratio of the first and the second syllable rhymes within the foot. The ratio is robustly 2/3 in Q1, 3/2 in Q2, and 2/1 in Q3 (Lehiste, 2003; Lippus et al., 2013).

Additionally, quantity is marked by pitch movement: In Q1 and Q2 words, the peak of the pitch contour is at the end of the first syllable, while in Q3 it is located at the beginning of the first syllable (Lehiste, 2003; Lippus et al., 2011; Lippus et al., 2013). Vocalic quality has also been shown to vary along with the quantity (Eek & Meister, 1998), and it is significant for distinguishing Q1 from Q2 and Q3 (Lippus et al., 2013).

From the phonological point of view, the Estonian quantity distinction has also been a subject of discussion regarding moraic interpretation. Fitting the Estonian three-way quantity contrast within the frames of moraic theory appears to be a challenging task. Provided that a maximum number of moras a syllable can consist of is two, the ternary contrast should be fitted into a bimoraic space, i.e., trimoraic syllables are not allowed. Thus, the main issue regarding Estonian quantity lies in the representation of long and overlong syllables. Hint (1973) and Prince (1980) have treated Q1 and Q2 syllables as monomoraic and Q3 as bimoraic, but Prillop (2013) points out the contradiction of short and long vowels which would both be monomoraic in that case.

The easiest way of describing Estonian quantities would be to use trimoraic syllables, as has been done by Hayes (1995), who links stressed Q1, Q2, and Q3 syllables with one, two, and three moras respectively. Alternatively, Bye (1997) has also used mono-, bi-, and trimoraic syllables, but for keeping the maximum number of two moras in a syllable, he suggests using extrasyllabic moras according to which the third mora of Q3 is either a free mora (does not belong to the syllable) or part of a degenerate syllable. Similarly, Eek and Meister (2004, pp. 351–352) propose that Q3 could constitute a syllable followed by a degenerate syllable which together form a separate foot. However, these theoretical approaches use trimoraic vowels and are not fully supported by phonetic measurements as the difference between trimoraic vowels in Q3 and monomoraic vowels in Q1 is too big, as is the difference between Q2 and Q3 syllables (Prillop, 2015).

Another possibility suggested by Eek and Meister (2004) is that the Q1 syllable is monomoraic and the Q2 and Q3 syllables are bimoraic with the difference between the latter two being in the mora sharing of Q3 syllable nucleus and the coda, whereas this does not happen in Q2 syllable. While Eek and Meister considered the second component of a diphthong as the coda, this approach does not fit well in the case of long vowels that would still be trimoraic (Prillop, 2013).

According to Prillop (2015) the representation of three-way distinction of consonants would be better explained by the possibility that coda consonants can either be linked to a mora or not. In Q2 syllable, coda consonant could not be considered moraic, while the coda consonant could be linked to a mora in Q3. This representation is not suitable for diphthongs (the second part of a diphthong would have to be reduced) nor for long vowels (it would assume monomoraic long vowels).

Considering previously discussed issues concerning the representation of Estonian three-way quantity distinction from the perspective of moraic theory, the question arises whether using a unit of mora is adequate in Estonian. Lehiste (1990) has compared Estonian and Japanese in terms of the temporal structures of poetry and concluded that in Estonian mora is not an isochronous unit of timing as it is in Japanese. She points out that timing in Estonian is connected to syllables, and that the basic rhythmic unit is a disyllabic sequence. This hypothesis is also supported by numerous phonetic findings about Estonian quantity.

The latest phonological descriptions of Estonian three-way quantity system (Prillop, 2013, 2015) have also taken phonetic facts into account and have been based on the approach of the ternary system being manifested in a disyllabic foot as a whole. Feet are disyllabic for Q1 and Q2, but the stressed syllable of Q3 constitutes a foot alone, so the following unstressed syllable is reduced because it does not belong to the foot. The final-lengthening at the end of the Q3 syllable and at the end of the Q1 foot is caused by the strong mora. Incorporating the Iambic-Trochaic Law (Hayes, 1995) Prillop (2013) expands on Kager’s (1993) idea of weak and strong moras and suggests the opposition of weak and strong moras for Estonian. Strong moras are phonetically described with longer or more intense sounds. Therefore, Q1 and Q2 feet have a strong mora in the second syllable (where the vowel is lengthened) and Q3 feet have a strong mora in the first syllable. Stressed Q1 syllable is monomoraic and stressed Q2 and Q3 syllables are both bimoraic, wheras the difference is in the location of the strong mora.

1.3. Previous articulatory studies of Estonian

Research done on articulatory aspects of Estonian quantity is relatively scarce and most of it dates from the 1960s and 1970s. In his pioneering articulatory study of quantity on Estonian vowels, Liiv (1961) found a substantial difference in the spatial extent of gestures between short and long vowels on the one hand and overlong ones on the other (although some methodological shortcomings have later been identified; Eek, 2008, pp. 67).

Eek (1970a, 1970b, 1970c, 1971a, 1971b, 1971c) studied the articulation of Estonian sonorant consonants (/n, nʲ, l, lʲ, m, r/) in three quantity degrees using different methods (X-ray, palatography, cinefluorography, and filming of lip articulation). The sonorants occurred in sentence-initial and in isolated words in the /ɑ-ɑ/-context, and also in a word-final position. His studies show that contact area and stiffness (estimated from cinefluorographic film) of articulatory movement increases with longer duration of the consonant, while the lip aperture is narrowing. However, there is no clear three-way distinction in the articulatory characteristics. In the case of /n/ and /l/ in Q2 and Q3, the contact area between the tongue and the palate is larger than in Q1. Linguopalatal contact is also wider for /r/ in higher quantity degrees. There is more variation in lip aperture; for /n/, with an increasing duration of the consonant it is either decreasing (3 subjects out of 5) or increasing (2 out of 5); for /l/ the lip aperture estimates in Q1 and Q2 are of similar length, but for Q3 there is more variation between subjects. With increasing quantity of /r/ Eek reports a regular narrowing of the lips. When making comparisons between consonants, differences between sonorant groups can be found. In the same quantity degree there is always a longer alveolar contact for /l/ than for /n/. The biggest area of lateral contact is found for /r/. The lip aperture is wider for /l/ and /r/ than for /n/.

The speed of the articulatory movements from a vowel to a following consonant is the slowest in Q1 and the fastest in Q3 (for both /n/ and /l/). Faster speed for Q3 sonorant shows greater muscular effort. This is also the case for the bilabial nasal /m/, which is pronounced more tensely in Q3 than in Q1 and Q2.

In general, Eek concludes that while the difference between Q1 and Q2 is primarily in the durational characteristics, Q3 is realized by significantly faster articulatory movements. In overlong consonants the first, syllable final component is produced with greater muscular effort, so the beginning of the consonant is tense. In the case of a long consonant, the syllable final component is lax. This is in accordance with the idea of virtual target (Löfqvist & Gracco, 1997; Löfqvist, 2005) suggesting that the position of the virtual target for the lips is varied in order to control the duration of closure/constriction, meaning higher target and bigger amplitude for long consonants. Since displacement is claimed to strongly correlate with velocity, long consonants should also have higher peak velocity. While Eek’s findings seem to support the hypothesis for both the displacement and velocity, Löfqvist (2005) found no differences in velocity when examining the production of Japanese and Swedish labial stop and fricative consonants varying the duration of the oral closure/constriction (long and short). Thus, Löfqvist concluded that for keeping the contact between lips longer, speakers vary both the position of the virtual target and its timing by modifying the deceleration of the lower lip movement.

Lehiste et al., (1973) used electromyography (EMG) for examining the activity of the orbicularis oris muscle during the production of bilabial single and geminate Estonian consonants in intervocalic position and at word boundaries. The results showed a difference in progressive closure duration of bilabials in all three quantity degrees. The authors also bring out the two-phase theory of geminate production according to which the first phase includes a syllable final occurrence of the consonant; the second phase is rearticulated and it starts the next syllable (forming a syllable-initial consonant). The analysis of EMG data suggests that there is a difference between long and overlong consonants, which exhibited a ‘rearticulation’ in their production, i.e., EMG signal revealed two successive peaks for a long consonant.

In a recent palatographic study on Estonian sonorant consonants, Meister and Werner (2015) compare the results obtained using a contemporary EPG system with Eek’s findings from the 1970s. They conclude that the articulatory characteristics of sonorants have stayed the same during the years. Similar to Eek, the authors confirm that higher quantity degrees are accompanied with larger contact area of the articulators involved. Nevertheless, there are some differences between the studies. The new results show a different size of the contact areas for /n/ in Q2 opposed to Q1 and Q3, as compared to Eek who claims that Q1 differs from the other quantities. Meister and Werner’s (2015) data also show a three-way distinction for the palatalized /l/.

1.4. Context-dependency and research questions

The syllable rhyme duration ratio—a traditional and robust way of describing the quantity distinction in Estonian—has been typically ascertained within similar segmental context (e.g., Eek & Meister, 2003; Lippus et al., 2009) or by ignoring the segmental context by randomly pooling different phoneme combinations together (e.g., Lippus et al., 2013). At the same time, the intrinsic properties of sound segments, claimed to have rather a psychophysiological than language-specific nature (Lehiste, 1970), have been shown to have non-linear effect on the quantity-related duration variability in Estonian. Eek (1974) has demonstrated that while /t/ is shorter than /p/, the ratio between the segments in Q1, Q2, and Q3 is also different: For /p/ it is 1 : 1.3 : 2.1, and for /t/ 1 : 2.0 : 2.9. As for perception, consonant context does not have a significant effect on the following vowel, but vowel quality can shift the perceived short-long category boundary earlier for /i/ than for /ɑ/ (Meister et al., 2011).

Lippus and Šimko (2015) investigated context-sensitivity using the acoustic data of the material described in Section 2 of the current paper (see below). They show a strong influence of the intrinsic characteristics of segments on the temporal patterns of quantity combinations. In all quantity degrees /p/ is longer than /t/. Regarding vowel context, /ɑ/ is longer than /i/, but there is a non-linear pattern associated with vowel quantity of the first syllable. The interaction between vocalic and consonant context somewhat neutralizes the word-initial consonant context, but vocalic context effect gets stronger in the interaction with the consonant. Importantly, the durational differences marking the quantity contrast are in some cases not robust enough to make these contextual effects negligible; the contextual effects need to be taken into account by the listeners and ‘compensated away’ in order to correctly assess the quantity pattern of a given stimulus. These results raise a question about the extent that individual influences on the rendition and parsing of various speech items varying in segmental context and quantity can be interpreted in terms of a system of discrete ‘phonological’ contrasts.

In this work we extend these investigations of context-dependency of quantity marking in Estonian to its articulatory aspects. We ask how relationships among kinematic characteristics reflect different quantity patterns in Estonian in different segmental contexts:

1. Is the Estonian three-way quantity contrast manifested by a corresponding three-way distinction in articulatory characteristics?

2. What are the articulatory correlates of quantity in terms of adjustments of gestural kinematic characteristics and an intergestural coordination measure to different quantity patterns?

3. How does segmental context influence articulatory characteristics and coordination and, mainly, to what extent does its influence interact with quantity correlates?

Guided by these questions, our primary aim is to evaluate the robustness of articulatory characteristics of the phonological quantity contrast with respect to the variation of speech material. To address these issues, we present an analysis of articulatory material consisting of renditions of CVpV stimuli in all 7 contrastive patterns of the Estonian quantity system. The initial C is a bilabial /p/ or an alveolar /t/ and the vowels are /ɑ/ or /i/ (only the two conditions with different vowels within a stimulus were recorded). These variables—stimulus initial consonant and vowels flanking the stimulus internal consonant /p/—present the segmental context relevant for question (2).

Three articulatory gestures are included in the analysis: The lip opening and lip closing gestures for stimulus internal /p/ and the intervocalic transition gesture between the flanking vowels. These gestures were chosen as they are deemed to appropriately represent the articulatory events related to quantity contrast and, unlike the other remaining lingual gestures, do not a priori involve immediate interaction with multiple contextual elements. That is, while, for example, intervocalic transition is primarily coproduced with /p/, it can be fully characterized by a movement from /ɑ/ to /i/ or from /i/ to /ɑ/. On the other hand, the tongue movement towards the first vowel is coproduced with either /p/ or /t/ as well represents one of the two possible transitions between vocalic segments.

For each of these gestures, we only report data pertaining to three ‘raw’ kinematic characteristics: Duration and spatial extent of each gesture, and peak velocity. We refrain here from including ‘derived’ measures such as stiffness estimates, c-parameter (Ostry & Munhall, 1985) or peak-to-peak ratio (Harrington et al., 1995), etc. Apart from parsimony’s sake, the main reason for this decision is that we do not at this stage commit to necessary theoretical underpinning of gestural dynamics associated with these measures, as this work is one of the first large-scale investigation of articulation in the Estonian three-way quantity system. We plan to address the questions of intergestural stability and other dynamic characteristics of articulation in subsequent work.

3.1. Acoustic duration of intervocalic stop

The acoustic duration of closure for the intervocalic bilabial stop /p/ is influenced by the consonant quantity (CL Effect) with consistent increase in closure duration with higher quantity degree showing a three-way distinction (p < 0.001 for all of the comparisons; see Appendices A11 and B11 for full results of statistical modeling and the x-axis of Figure 5 for the duration of oral closure). While vowel lengthening (VL Effect) has no significant influence on the acoustic duration of the intervocalic stop, the stimuli with both vowel and consonant lengthening (VCL Effect) reflect the ternary effect of consonant quantity (p < 0.001 for all comparisons, except p < 0.01 for Q1 and Q2 stimuli pipɑ—piːpːɑ, tɑpi—tɑːpːi tipɑ—tiːpːɑ). Regarding vocalic (/ɑ-i/ vs. /i-ɑ/) and consonantal (/p/ vs. /t/) context effects, basically none of the differences are significant; the duration of the intervocalic stop is longer for tɑːːpi compared to pɑːːpi (p < 0.05).

3.2. Lip closing

The results for the lip closing gesture are shown in Figure 2 with the duration (x-axis) and displacement (y-axis) depicted in the upper three panels and the measures for the peak velocity at the bottom.

Figure 2

Lip closing gesture. The kinematic characteristics are estimated for the duration, displacement (upper panels), and the peak velocity (bottom) of the articulatory movements. The panels show the stimuli with the CL Effect (left), VL Effect (mid), and VCL Effect (right).

3.3. Lip opening

The results for the lip opening gesture are shown in Figure 3.

Figure 3

Lip opening gesture. The kinematic characteristics are estimated for the duration, displacement (upper panels), and the peak velocity (bottom) of the articulatory movements. The panels show the stimuli with the CL Effect (left), VL Effect (mid), and VCL Effect (right).

3.4. Tongue transition

Figure 4 shows the results for the kinematic characteristics of the lingual gesture of transition between the vowels surrounding the bilabial consonant.

Figure 4

Tongue transition gesture. The kinematic characteristics are estimated for the duration, displacement (upper panels), and the peak velocity (bottom) of the articulatory movements. The panels show the stimuli with the CL Effect (left), VL Effect (mid), and VCL Effect (right).

3.5. Lip-tongue coordination

Figure 5 depicts the results for the coordination between lips and tongue, i.e., the temporal interval from the onset of the lip closing gesture for the bilabial consonant to the onset of the lingual gesture for the following vowel.

Figure 5

Closing gesture displacement vs. the duration of C2-onset-to-V2-onset interval. The panels show the stimuli with the CL Effect (left), VL Effect (mid), and VCL Effect (right).

The interval between the onsets of the gestures is influenced by both consonantal and vocalic quantity in the /ɑ-i/ vocalic context. As can be seen from Figure 5, the duration of the interval (y-axis) is increasing with growing consonantal length and decreasing with vowel length. The differences induced by CL Effect are significant for the Q1—Q3 pair pɑpi—pɑpːːi (p < 0.001) and for /t/-stimuli tɑpi—tɑpːi—tɑpːːi forming a three-way distinction (p < 0.01 for Q1—Q2, p < 0.001 for Q2—Q3 and Q1—Q3 comparisons). A shortening effect of VL on the interval duration shows a two-way opposition of Q1 and Q2 vs. Q3 for both triplets with /ɑ-i/ vocalic context (p < 0.01 for pɑːpi—pɑːːpi, pɑpi—pɑːːpi, tɑːpi—tɑːːpi, p < 0.001 for tɑpi—tɑːːpi). In the case of the stimuli contrasting in both CL and VL (the rightmost panel in Figure 5), the temporal interval between lip-tongue gestures does not differ among the triplets.

As for the Vocalic Context Effect, the interval is generally longer in /ɑ-i/ than in /i-ɑ/-stimuli in words with consonant lengthening (p < 0.001 for pɑpːːi—pipːːɑ, p < 0.05 for tɑpi—tipɑ, p < 0.001 for tɑpːi—tipːɑ and tɑpːːi—tipːːɑ), and the reverse pattern emerges in stimuli with Q3 vowel (p < 0.001 for pɑːːpi—piːːpɑ and tɑːːpi—tiːːpɑ). Consonant Context Effect shows a linear trend: With the /t/-context, the temporal interval between the gestures is consistently longer than with the /p/-context. Nevertheless, the differences are significant for the /ɑ-i/ vocalic context for stimuli differing in consonant length, tɑpi—pɑpi, tɑpːi—pɑpːi, and tɑpːːi—pɑpːːi (p < 0.001).

There is no overall effect of the repetition of a stimulus on the interval duration between the lip-tongue gestures. The only significant, but minute differences emerge for pɑpːːi (p < 0.05) where the gesture gets faster with the repetition and for piːːpɑ (p < 0.05) with a slowing effect.