The evidence for isochrony of stress timing is weak for ordinary prose, but this does not mean that the timing of stresses is always unaffected by global constraints. We asked subjects to continually repeat the phrase "Take a pack of cards" and to temporally align the words "take" and "cards" with an auditorily presented stimulus consisting of just the words "take" and "cards" repeated several times. The phase of the "cards" stimulus relative to a reference cycle defined by the "take"-"take" interval was varied over the range 0.3-0.65 in eight equal-sized phase steps. The distribution of produced phases for the vowel onset of the syllable "cards" was trimodal: subjects showed a powerful preference for phases close to 0.5 and somewhat weaker preferences for phases near 0.36 and 0.6. These values are close to those predicted by a harmonic model for stress timing. The distribution had this form whether the subjects were speaking along with the stimulus or trying to maintain the prescribed timing after cessation of the stimulus. The observed phase was influenced by the phase produced on previous trials, suggesting dynamic control with hysteresis between competing stable patterns of timing. These results demonstrate strong rhythmic constraints on the timing of stresses within a phrase. Modeling these constraints should provide insight into the form of a general dynamic control regime for global speech timing, and may allow improved characterization of natural timing patterns in English speech.
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