Lexical stress

Some syllables sound stronger or heavier than others. For instance, taking a word such as TABLE, we can say the first syllable of this sounds stronger than the second. This contrasts with a word like machine, where we find the second syllable sounds stronger than the first. Because of these types of distinctions, we view stress as being a property of syllables rather than of phonemes 

It is important to note that the term stress is used in a number of different ways in the linguistics literature. The most fundamental distinction is between lexical stress and sentential stress. Lexical stress is a core property of a word, and as such doesn t change. In our previous example, TABLE is stressed on the first syllable while machine is stressed on the second and these are properties of the words themselves. Sentential stress on the other hand describes the effect whereby one syllable in the sentence receives more stress than the others and this is normally due to some pragmatic or communication reason, and is not a fundamental property of the word itself (e g. 1 SAID 1 WANTED THAT ONE. We shall ignore this second type of stress for now as this is dealt with in detail in Chapter 8. 

We can identify a third category called reduced. This is mainly used to indicate the stress level of syllables containing the schwa vowel. Reduced vowels occur in at least three subtly different cases. First, some words naturally, or always, have a schwa in a certain position, for example in the first syllable of machine / m ax sh iy n/. But consider the second syllable of information. We have given this a schwa in our annotation and most speakers would agree with this pronunciation. Now consider the word inform, /ih n f ao r m/, here the second syllable is a normal full vowel. We can say that information is created from inform by the application of morphological rules, and in the process, the second syllable has been reduced from a full vowel to a schwa. A third form of reduction occurs in function words, when for instance a word such as (from, / f r ah m/ is produced as /f r ax m/ in many instances. Finally, when people speak quickly, they often under-articulate vowels, which leads to a loss of distinction in their identity leaving them sounding like a schwa. This effect is also termed reduction. The number 0 is used to represent a reduced vowel, so the full transcription for information is /ih2 f axO r m ey2 sh axO n/ 

In English, stress is a fundamental part of the pronunciation of a word, and as such weakens our the notion we have been adopting until now that a word s pronunciation can be repre- 

Stress can be graphically represented in the sort of tree used to describe syllable constituent structure. In our previous example the nodes at the syllable level were unlabelled we can now show the same tree but with stress labels at the nodes  

An alternative to the use of absolute levels of stress, such as primary and secondary, is the theory of metrical stress [284], [286] in which stress is pinely relative. In this, a binary tree is used to represent each word and within this each syllable is defined as either strong or weak. So information would be defined as 

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Emphasis, prominence, accent and stress are all terms used to indicate the relative strength of a unit in speech. These terms are used with a variety of definitions in the literature, so to avoid confusion we will use these these terms as follows. Stress indicates lexical stress, which is an inherent property of words, and indicates for instance that the first syllable in table is stronger than the second, while the second syllable in machine is stronger than the first. We discuss this type of stress more fully in the section on phonology in Chapter 7. Prominence is used to indicate the strength of a word, syllable or phrase when it is used in a sentence. We will use the term accent solely to indicate intonational phenomena associated with pitch, and emphasis to indicate a specific use of prominence in discourse. 

Prominence is really a properly of words, such that one word is given extra strength compared to its neighbours. This however is manifested in the lexically stressed syllable of that word receiving the extra strength, rather than all the syllables of the word. It is widely accepted that some, but not all, of the prominence pattern in a sentence is governed by the syntax within that sentence. 

If lexical stress is a relative phenomenon, what of single syllable words As there are no other syllables to contrast with, the stress status of such words is technically undefinable. However,... 

Lexical stress is manifested at the syllable level. Exactly one syllable in a word is designated as the primary stressed syllable, all other syllables have either secondary stress or are reduced. 

Black and Hunt in fact used a linear regression technique, with features such as lexical stress, numbers of syllables between the current syllable and the end of the phrase, identity of the previous labels and so on. Once learned, the system is capable of generating a basic set of target points for any input, which we then interpolated and smoothed to produce the final FO contour. Other data driven techniques such as CART have proven suitable for S3mthesizing from AM representations [292], [340],... 

If lexical stress is a relative phenomenon, what of single-syllable words Since there are no other syllables to contrast with, the stress status of such words is technically undefinable. However, by convention, most of these words are given a primary stress or strong stress in their syllable. The exception is content words, which are given a primary stress if in their full form (/f r ah m/) or no stress in their reduced form (/f r ax m/). 

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