The effects of differential vowel prolongations on perceptions of speech naturalness

Prolongation of speech sounds is currently used to modify stuttering and en hance fluency. Prolonged speech (PS) (e.g., prolonged vowels, prolongation throughout utterances) is, however, often perceived as unnatural by listene rs. This study examined at which durations and in which contexts 52 college students (primary language was American English) perceived PS to be unnatu ral. Stimuli were limited to controlled variation in prolongation of the vo wel in the middle single-syllable word of a carrier phrase (i.e., say word again). The prolongation was effected by digital waveform manipulation with in the Kay Elemetrics Computerized Speech Laboratory (CSL). The listeners j udged if they strongly agreed, agreed, or disagreed that the phrases sounde d natural. Results indicated that the extent of vowel duration (and possibl y context) does influence listener's perception of speech naturalness, find ings which can be applied to facilitate fluency therapy. Educational objectives: (1) The reader will learn about and be able to summ arize the digital waveform manipulation procedure in the study. (2) The rea der will learn about and be able to describe the effects of differential vo wel prolongation on listener's perception of speech naturalness. (3) The re ader will learn about and evaluate how differential vowel prolongation can be used to enhance fluency. (C) 2001 Elsevier Science Inc. All rights reser ved.