As stated in the preceding chapters, the prosodic organization of an utterance involves voice quality changes. The main goal of the experiment described further below is to validate the use of electroglottography in distinguishing voice qualities on the linguistic layer of communication. It will be shown that the important features of laryngeal behavior change along with linguistic prosodic gestures and that this correlation may be registered by means of electroglottography. The examination presented here is limited to German, although a comparison with other languages is also included.
The study of linguistic prosody involves the suprasegmental features of speech. One such feature is stress which is perceived as the stronger prominence of some unit compared to other units.
Linguistic stress is considered to be a specific implementation of a constituent structure. The structure is built on prosodic domains, such that each smaller domain is included within the next larger one, constituting a prosodic hierarchy. Thus, for a specific element (vowel, syllable, mora, phonological word, clitic group, phonological phrase and prosodic utterance) to be stressed it is required that this element is a "designated" member of a constituent structure (Dogil, 1995). Word stress is defined as a prominence relation between the syllables (and metrical feet) of a phonological word. For a syllable of a phonological word to be stressed it needs to occupy a relatively stronger position in the metrical constituent structure than other syllables of the same word. The strength of the relations within a single phonological word may be directly coded into the metrical tree or may be derivable from other parameters of the metrical grid (Hogg & McCully, 1987). Even in such systems where the stress assignment of a given constituent is partially predetermined by the morphology of the element designated to carry the word stress (e.g. Russian, Lithuanian), the element receives stress due to the principles of the independent metrical constituent structure. Of the numerous prosodic constituents only two can be validated in experimental studies on German prosody (Möhler & Dogil, 1995):
- the stress foot (the basic linguistic category at the level of word prosody (word stress)),
- the intonational phrase (the basic linguistic category at the level of phrasal prosody).
The cues to stress are identified in the areas of perceptual, articulatory and acoustic phonetics. In the auditory dimension, stress is characterized by the higher prominence of the designated element. Prominence means that the element is perceived as standing out of the linguistic context. According to the standard definition, prominence is a product of the length, loudness, pitch (and its movement) and quality of the designated element. These auditory quantities have correlates in acoustic signal properties such as duration, intensity, fundamental frequency and spectral structure.