Rhythmical Factors in Stress Shift

In phrases such as THIRteen MEN, stress in the first word is shifted forward from its canonical word-final position. Our general hypothesis is that this stress shift is controlled in part by the global rhythmical pattern of the utterance, informally defined as a Rhythmic Constraint on onset times of stressed vowels, in real time. This hypothesis yields two specific predictions about the occurrence of stress shift. First, stress shift should depend on preceding contexts as well as following contexts. Second, stress shift should be more frequent at faster speaking rates. These predictions were tested using ‘shiftable’ number words, preceded by words that are metrically wS, Sw or Sww. These two-word phrases were read in a list, at various speaking rates controlled by a metronome. The resulting proportions of stress shift verify both predictions. First, stress-shifted realizations are most frequent after Sww words, and less frequent after Sw or wS words. Second, for SS number words, the proportion of stress-shifted realizations increases with faster speaking rate. In addition, for Sww number words, speakers restructure the whole phrase, yielding low incidence of stress shift. These results support the existence of a Rhythmic Constraint that explains why and when stress is shifted.