Perception of Segment Duration in Sentence Contexts

Abstract

A category judgment technique has been used to quantify the preferred duration for phonetic segments in words placed in different syntactic environments. Sentences containing the stressed vowel Iii of v the word "deal" and the postvocalic fricative lsi of the word "fish" were modified by deleting or duplicating portions of the waveform from the phonetic segment in question. Results indicate that listeners adjust their expectations of segment duration depending on the syntactic position of the word in the sentence. In particular, the segmental lengthening that is seen in the production of a phrase-final syllable is represented in a listener's perceptual scheme. The data were further examined in order to determine the just-noticeable difference (JND) for a change in duration to a single segment, in a randomized set of different sentences. The JND was found to be 25 msec or more. JND differences between sentence environments suggest the following constraints on the perception of durational information: (a) sensitivity to changes in duration is best for phonetic segments in non-word-final syllables, (b) sensitivity is influenced by a backward masking effect of any following words, and (c) the offset time of an utterance-final fricative is particularly difficult to perceive.