Working paper Open Access
Speech utterances are comprised of hierarchically organized units, such as features/gestures, segments, moras, and syllables. Why these units are organized hierarchically is not well understood; phonological theories vary widely in their treatment of them, and models of speech production ascribe them diverse roles. This paper presents a selection-coordination theory of phonological structure, which attempts to unify our understanding of phonological units and explain why they are organized hierarchically. The theory holds that hierarchical organization emerges from a recurring trend in speech development whereby children acquire coordinative regimes of control over motor plans that were previously competitively selected, with transitions from competitive to coordinative control being made possible by the internalization of sensorimotor feedback. In this framework, segments, moras, and syllables are understood as differently-sized instantiations of the same type of motor planning that have differing roles in the course of development; diverse phonological patterns are given a cognitively grounded account that derives from distinguishing competitive and coordinative regimes of articulatory control. Evidence for the theory is drawn from research in motor control, phonological development, and phonological and phonetic patterns in adult speech.
To begin with an analogy, consider how notes on a piano can be played: piano keys can be pressed one after another, such that the notes are produced in a sequence. Alternatively, several keys can be pressed together as a chord, potentially with leading or trailing grace notes. The sequence of notes corresponds to a mode of competitive control in which actions are planned in parallel but produced sequentially; the chord corresponds to a mode of coordinative control, where actions are selected together and produced with precisely controlled relative timing. These two control regimes are fundamental to motor control generally, and distinguishing between them provides insights into the structure of speech utterances and phonological patterns. The selectioncoordination theory presented here holds that there are two distinct cognitive mechanisms involved in control of speech articulation—selection and coordination—and that the interaction between these mechanisms results in two prototypical regimes of control: competitive selection and co-selection/coordination.
Young children are not equally competent in utilizing competitive and coordinative control. Pursuing the piano analogy, children initially learning to play tend to press keys one at a time, relying on competitive control. Subsequently they develop coordinative control: they learn to play sets of notes and patterns in which relative timing is more exactly governed. Competitive control developmentally precedes coordinative control. In the domain of speech, the consequences of this are of profound importance to our understanding of phonological structure: over the course of development children acquire coordinative control over speech gestures that were previously competitively controlled, thereby learning more complex and highly coordinated control structures. The hierarchical structure we observe emerges from this developmental progression. An important consequence of the theory is that phonological units, such as features/gestures, segments, moras, and syllables, are ultimately not so different from each other: all of these are sets of gestures, and what distinguishes them is when in the course of development coordinative control over those gestures is acquired.
In this paper we elaborate the selection-coordination theory, drawing evidence from research in motor control, phonological development, and phonological and phonetic patterns in adult speech. Section 1 presents the distinction between selection and coordination of movement plans and examines how these concepts have been incorporated into models of speech planning and production. Section 2 reviews literature on speech development and identifies a recurring pattern in which coordinative control is acquired over articulatory gestures that were previously competitively selected. Sections 3 and 4 examine phonetic and phonological variation associated with segments and moras from a motoric and developmental perspective. Section 5 further expands upon the relation between development changes in control, hierarchical structure, and phonological patterns.