The articulation of labialisation

capable of measuring the position of the lips is Electromagnetic Articulography (EMA). Given the fact that EMA sensors can be placed on multiple articulators, e.g., the tongue tip, the tongue body and the lips, it is possible to measure their temporal coordination (Kochetov, 2020). However, as Noiray, Cathiard, Ménard, and Abry (2011) pointed out, lip shape and constriction cannot be adequately tracked with flesh-point measures alone. As a result, Noiray et al. (2011) supplemented flesh-point tracking with a video shape tracking system, in which the lips are painted in blue to maximise the colour contrast with the skin (Lallouache, 1991). In post-processing, the blue lip shapes are tracked to calculate lip aperture, interlabial area and lip protrusion (Noiray, Ries, & Tiede, 2015).

An ideal technique would naturally be one which allows us to capture and measure the entire vocal tract with a sufficiently high temporal and spatial resolution, which is currently technologically challenging, costly, and relatively invasive (Kochetov, 2020). Advances in real-time MRI technology may make entire vocal tract measures more of a possibility in the near future. Indeed, recent MRI studies have been undertaken which consider labial articulation including Proctor et al. (2019) onAmerican English/r/. However, data collection and analysis is particularly challenging and as a result, sample sizes tend to be small.

3.3 The articulation of labialisation

The vast majority of existing phonetic descriptions of labialisation consider the lip rounding occurring in vowels. There is a known relationship between the implementation of lip rounding and both the vertical and the horizontal position of the tongue in vowels. Firstly, it is generally agreed that lip rounding in vowels is not realised uniformly across vowel heights (e.g., Catford, 1977; Lindau, 1978; Linker, 1982; Pasquereau, 2018). The higher the vowel, the smaller the degree of lip aperture. A high rounded vowel, such as[y], usually has a smaller lip opening than a lower rounded vowel, such as [ø]. This is probably due to mechanical reasons: it is hard to maintain close lip rounding when the jaw is opened. Secondly, accounts as early as Sweet (1877) indicate that lip rounding in vowels varies as a function of the frontness of the tongue. Two distinct configurations are generally described. One possibility is to form a small

lip aperture or a ‘small tunnel’ (Catford, 1988, p. 150) with the inner surfaces of the lips by bringing the lip corners in towards the centre horizontally. In this position, the lips have a

‘pouted’ configuration (Catford, 1988; Sweet, 1890). This type of rounding is associated with back vowels such as[u]and [o] and has been termedinner roundingby Sweet (1890),horizontal lip rounding by Heffner (1950) andendolabialby Catford (1988). Rounding of this sort involving a horizontal constriction of the space between the lips is predominantly associated with the contraction of the orbicularis oris muscle (Laver, 1980), as described inSection 3.1(p. 76). The alternative lip rounding configuration is presented in relation to front rounded vowels like[y]

and[ø], in which the lips are brought together vertically by closing the jaw (Ladefoged, 1971).

While the side portions of the lips are in contact, a ‘slit-like flat elliptical shape’ (Catford, 1988, p. 150) gap is left in the centre. This configuration has been namedouter roundingby Sweet (1890),exolabialby Catford (1988) andvertical lip roundingby Heffner (1950). The muscles implicated in this vertical compression of the lips include the inferior orbicularis oris and the mentalis, as well the raising of the jaw, as described inSection 3.1(p. 76).

Ladefoged (1971) argued that a better pair of terms for the two types of rounding may belip rounding, which would include lip protrusion, andlip compression. Lindau (1978) also distinguishes lip rounding, which for her is synonymous with lip protrusion, from lip com-pression. Accounts of lip protrusion vary, which could be due to the frequency of the different types of rounding across the world’s languages. Heffner (1950) noted that ‘protrusion of the lips is often a concomitant of horizontal lip rounding. It is much less frequently found with vertical lip rounding’ (p. 98). Similarly, Laver (1980) remarked that lip protrusion is almost always accompanied by a certain degree of horizontal constriction of the space between the lips. However, he stressed that while substantial lip protrusion without horizontal constriction is physiologically possible, it is rare in the world’s languages. He even went as far as to suggest that the articulatory parameter that all rounded vowels and labialised consonants have in com-mon is the horizontal constriction of the inter-labial space. As a result, any labial articulation lacking a horizontal contraction would not be considered labialised by his view. Laver (1980) provided eight possible labial settings which deviate from a neutral lip position, which are

3.3. The articulation of labialisation 81

defined as combinations of horizontal and vertical expansion or constriction. He presented schematised representations of these settings, which have been recreated inFigure 3.2. As all eight settings may be accompanied by lip protrusion, there are in fact 16 possible deviations from the neutral labial setting. Laver (1980) explained that the most common labial setting in the world’s languages is one involving horizontal constriction and vertical expansion with protrusion, which is the ‘lip-rounded type of setting’ (p. 38). The high frequency of this lip configuration may be due to the fact that back vowels are ‘naturally’ rounded and front vowels

‘naturally’ unrounded (Lindau, 1978). Furthermore, front rounded vowels are quite rare. As Mayr (2010) highlighted, out of the 562 languages studied in theWorld Atlas of Language Struc-tures, only 6.6% are reported to have front rounded vowels (Maddieson, 2008). It is therefore not surprising that the most common lip action is the one associated with back vowels.

By combining the various phonetic accounts of the two main labialisation gestures described above, we define the main labialisation strategies as follows:

Horizontal labialisation: associated with back vowels, the lips are pouted by drawing the lip corners together to form a small, rounded opening.

Vertical labialisation: associated with front vowels, the lips come together by raising the bottom lip and closing the jaw, resulting in a small, slit-like opening.

Lip protrusion: the lips are pushed forward to extend the vocal tract.

As Laver (1980) suggested, bothhorizontal labialisationandvertical labialisationmay be accompanied bylip protrusion. We choose to avoid the somewhat loaded termroundedand employ instead the more phonetically neutral term labialisation, which can be applied to both consonants and vowels. We thus definelabialisationas a secondary labial articulation in consonants and vowels resulting in a reduction of the overall lip area. By including lip area in the definition, we ensure that lip spreading, which would increase lip area, cannot be considered a possiblelabialisationstrategy. However, we note that the size of the lip area of the two mainlabialisationgestures may vary. Presumably,horizontal labialisationwith its small, rounded opening has a smaller lip opening to that of vertical labialisationwith its slit-like

Figure 3.2:Schematisation of possible lip settings according to Laver (1980, p. 37). All lip settings may be accompanied by lip protrusion. The outline of the neutral lip setting is indicated by a

dashed line.H– Horizontal;V– Vertical;E– Expansion;C– Constriction.

3.3. The articulation of labialisation 83

opening. Differences in the area of the lip opening are also suggested in the eight possible lip settings according to Laver (1980), schematised inFigure 3.2. Lip area differences may have acoustic consequences. Another component oflabialisation,lip protrusion, which extends the size of the vocal tract, would also modify the acoustic output of speech. The acoustic effect of labialisationwill be discussed inSection 3.5(p. 84).

Detailed phonetic accounts oflabialisationin consonants are surprisingly hard to come by.

Most descriptions are phonological in nature in that they state whether or not a consonant is labialised, without going into details concerning the exact configuration of the lips. With regards to English consonants, it is generally agreed that the velarapproximant/w/and the post-alveolar sibilant fricatives /S, Z/ are produced with labialisation. Descriptions of the post-alveolarapproximant/r/may also includelabialisation, which we described in more detail inChapter 2(p. 35). As/w/is the semi-vocalic counterpart of/u/, it is assumed that/w/and /u/share the same labial properties. Some researchers have suggested that the post-alveolar sibilant fricatives have a different lip posture to that of/w/. Toda, Maeda, Carlen, and Meftahi (2003) studied lip patterns in both English and French using 3D facial motion-capture data from three subjects (one American, two French) producing nonsense words. They measured the front-back position of the lips and the approximate lip area in order to evaluatelip protrusion and ‘rounding’. They suggested that ‘labialisation’ can be specified by two lip components.

Both the post-alveolar fricatives/S, Z/and the velarapproximant/w/are produced withlip protrusionby all subjects, but the two consonant groups are opposed concerning lip area,/w/

being closed by rounding, unlike the post-alveolars which are described as ‘open’. We can thus make a connection between Toda et al. (2003)’s two lip components in labialised consonants and the two possible lip shapes in rounded vowels previously described. Toda et al. (2003)’s description of/w/ is suggestive ofhorizontal labialisation, while /S, Z/without ‘rounding’

may bevertical labialisation. Brown (1981) also noted the similarity between labialisation in consonants and rounding in vowels. Inspired by Sweet (1877)’s description of ‘inner’ and ‘outer’

rounding, Brown also suggested that there are two lip gestures used for English labialised consonants: while/w/is ‘rounded’,/S, tS, Z, dZ/and/r/are ‘protruded’.