Rhythmic constraints on stress timing in English

Rhythm in speech is interpreted as the hierarchical organization of temporally coordinated prosodic units. This is a departure from conventional phonetic approaches which have focused on isochrony. Speech cycling, a novel experimental vehicle for investigating rhythmic constraints, is introduced. In a speech cycling task, subjects repeat a phrase together with a periodic stimulus and the temporal distribution of onset events (beats) is examined. Two speech cycling experiments are presented which probe the degree to which the relative durations of inter-stress intervals within a series of repeated phrases are independent. The data reveal the presence of strong rhythmic constraints on stress timing which have hitherto eluded experimenters. It is argued that these constraints are evidence for a task-specific dynamical system in which prominent events (stress beats) are constrained to occur at specific, predictable, phases of an enclosing cycle. The dynamical system is characterized by entrainment between metrical levels, a principle which underlies rhythmic coordination in other activities such as locomotion. It is demonstrated that the hierarchical nesting of metrical levels arises inevitably within a repetition task, and what is more, the construction of individual prosodic units depends to some extent on the resulting rhythmic pattern. By structuring an utterance so that prominent events lie at privileged phases of a higher-level prosodic unit, rhythm is seen as an organizational principle which has its roots in the coordination of complex action and its effect in the realm of prosodic structure.