Changes in shape, space and time: the impact of position on the spatiotemporal and configurational articulatory properties of liquid consonants.

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The speech sounds 'L' and 'R' are often grouped together as a class (called 'liquid consonants'), because they are similar in a number of ways. For example, although they function as consonants in speech, they have a vowel-like phonetic quality. The are also among the most complex speech sounds to produce (and may be late acquired by children or hard for adult learners to master). They vary widely in different accents of the same language. Finally, their production can involve the tongue forming multiple constrictions in the vocal tract and they sometimes involve specific movements of the lips as well.Although speakers are not always aware of it, the 'L' sounds at the beginning and end of a word like 'level' do not sound exactly the same. Likewise the R' sounds at the beginning and end of a word like 'roar' (for those so-called 'rhotic' speakers who pronounce an 'R' at the end of 'roar' at all!) do not sound exactly the same. Behind the difference in sound quality is complex variation in (i) the way the articulatory organs synchronise their movements (ii) the strength of the production of the speech sound and (iii) the shape of the tongue when the speech sound is produced. When an 'L' or 'R' at the beginning of a word is pronounced, the speech organ movements involved tend to be more tightly synchronised than for an 'L' or 'R' at the end of a word. Also, 'L' and 'r' at the beginning of words are produced with more effort than they are at the ends of words. Finally, the tongue shapes involved in the production of 'L' and 'R' at the beginning and ends of words can be radically different from one another. These remarkable differences are very hard to measure, but research over many decades has addressed and raised a number of theoretical questions.Variation in these three parameters can cause very noticeable changes in the way 'L' and 'R' sound, explaining why, at the end of words, they seem less like consonants and more like vowels, e.g. making 'foal' and 'foe' sound very similar. The consonant might even disappear altogether, as occurred 200 years ago to 'R' at the end of the words in the RP accent of English. Thus, subtle variation in speech production can result in big changes in the long term. However, not all accents of English show the same patterns, or change at the same rate. While American and Irish English mostly have strong 'R' sounds at the end of words, word-final 'R' is starting to sound very weak and even be lost in some Scottish accents. This project will use a vocal-tract imaging technique, ultrasound tongue imaging (UTI), to directly study the way the tongue moves inside the mouth when it is producing 'L' and 'R', informing theories of speech articulation. The movement of the lips will also be recorded, as they play an important part in the production of English 'L' and 'R' too. We will record differences in the timing of movements of different parts of the tongue and the lips, how extreme the movements are and how different the shape the tongue is when it is producing 'L' and 'R' in different positions within the word. We will also look at what happens to 'L' and 'R' across longer domains too, as it has been shown that the greatest changes in the way these sounds are produced are found when 'L' and 'R' occur at the beginning and end of speech utterances longer than single words. We will study how changes in the movements of the vocal organs correlate with changes in the acoustic speech signal and we will identify which kinds of variation in vocal organ movement are most likely to make 'L' and 'R' sound weak, vowel-like or missing. Our research will focus on three key varieties of a single language in which 'R' is pronounced at the beginnings and ends of words, i.e. Scottish, Irish and American English. We will thus be able to address regional and historical variation within an otherwise well-understood language using novel methods to address theoretical questions relevant to all languages.