Kuzmenko T. Stressed Vowels' Reduction in Modern German Speech: an Experimental Phonetic Study.

This dissertation focuses on the systemic study of the German stressed vowels' variability. The thesis establishes linguistic and extralinguistic factors which cause the stressed vowels' modifications and alternations in prepared and spontaneous speech; it also determines the degree of the vowels differential markers' instability. Auditory, acoustic and statistical analyses enabled to ascertain quantitative and qualitative properties of the main variants of the vowels under research. The analysis of temporal and timbre characteristics of vowel in prepared and spontaneous speech has proved that stressed vowels undergo quantitative and qualitative reduction resulting in the instability of vowel phonemes' differential markers and the occurrence of their combinatory and positional allophones. Differentiation of vowels according to the horizontal position of the tongue remains stable. Changes in the vertical position of the tongue, the degrees of vowels' intensity and labialization vary considerably. The opposition of long and short vowels is most unstable. Essential influence on the stressed vowel phoneme's realization is rendered by their position in a rhythmical group and an utterance. Greater changes in the stressed vowels' actualization are registered in open and potentially closed syllables rather than in closed ones.