Consonant duration and stress effects on the P-centers of English disyllables

Abstract

Perceptual Centers (P-centers) refer to that phenomenon in a word that must be regularly spaced in time with respect to other P-centers in a sequence of words in order for the sequence to sound isochronous (Morton, Marcus, and Frankish, 1976). The P-centers of monosyllables have been found to be affected by the phonetic makeup of the syllable itself (Marcus, 1981; Fowler and Tassinary, 1981; Cooper, Whalen, and Fowler, 1986). In general, the longer a particular segment within a syllable (initial consonant, vowel, or final consonant), the later the syllable's P-center. This P-center is equidistant from the surrounding P-centers of other words. For example, if words are set in time to a metronome, their P-centers would align with the metronome beat since the beats are equidistant from each other. This thesis examines what determines the P-center locations within disyllabic English words (American dialect). Consonant lengths and stress patterns (foot type) are evaluated for their effects on the words' P-centers in a series of six production experiments. The results indicate that, like monosyllables, consonant length has a major effect on the location of disyllabic words' P-centers. And, initial consonants have a greater effect on their words' P-centers than either medial or final consonants. This finding supports Morishima's (1994) Onset-Tail model that was developed for Japanese disyllables. In addition to demonstrating the consonant length P-center effect in English disyllables, this thesis will also show that the disyllable's foot type affects its P-center. The interword intervals preceding trochees will be shown to be longer than those preceding iambs (a P-center effect). Therefore, the overall results of this thesis suggest that the P-centers of disyllables are affected by both their prosodic structure and their individual consonant lengths. The implications of this joint effect on words' P-centers will then be considered in light of the isochrony, timing, and slot literatures.