5 1. Physiological Foundations of Speech (Material to Dysarthria) airstream to the subglottal location in the larynx in order to produce an air column necessary for the correct functioning of the larynx and vocal folds (Shprintzen & Siegel-Sadewitz 1982; Minczakiewicz 1990). This is followed by phonation, in which the larynx plays the main role. Variations in phonation occur depending on the length and thickness of the vocal folds, as well as their position and vibrations during vocalization. The frequency of vocal fold vibration is unique for each person, corresponding to the pitch of the voice produced by the larynx (Ichikawa & Kageyama 1991). Another essential parameter of speech is the nasal/oral quality of a speech sound. The function of resonator is fulfilled by the vocal channel consisting of the oral cavity and pharynx (oropharynx), together with the resonating space of the lateral nasal cavities (nasopharynx) connected to the respiratory channel. The supraglottal space forms a cavity in which fundamental frequencies resonate as harmonic variants. The phoneme, in general, is a class of phonetically related speech sounds which do not co-occur in the same environment (see Wróbel, Dukiewicz & Sawicka 1995); to make the definition less abstract, cf. the explanation from Lyons: In English, p, t and k in certain positions of the word are slightly aspirated (that is, pronounced with an accompanying slight puff of breath); in other positions, after s for example, they are unaspired (cf. top : stop, pot : spot, etc.). In a broad transcription, therefore, the phonetician might well use the same letter (or other symbol) to represent both the English speech-sound (as indeed the alphabet used for English generally does), although they are quite easy distinguishable, phonetically. […] The reason why we can present both the aspired and the unaspired consonants with the same symbol in broad transcription is that the distinction between the aspired and the unaspired variety never has the function of keeping apart different words in English (this is a very crude, and partly inaccurate, statement of a principle that will be treated more fully later); it is not a functional difference: it is a phonetic difference, but not a phonological, or phonemic, difference in English […]. In cases of this kind we say that the phonetically distinguishable […] speechsounds are positional variants, or allophones, of the same phoneme. They are called positional variants because the occurrence of one rather than another of phonetic variants of a particular phoneme is determined by the position of the phoneme in the word. (Lyons 1968: 100–101) Phonemes fall into distinctive types, depending on the parts of the speech organs engaged (tongue, lips, cheeks, and soft palate): e.g. the nasopharynx
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