Summary and conclusion

This volume compares two very different approaches to modeling speech planning: Articulatory Phonology, with quantitative phonological representations and a set of phonology-intrinsic timing mechanisms, and XT/3C, an alternative model with non-quantitative symbolic phonological representations and general-purpose phonology-extrinsic timing mechanisms. It argues that the motor-control literature for both speech and non-speech supports the XT/3C approach, which expands on earlier models based on Generative Phonology to include a Phonological Planning Component to set the symbolic goals for an utterance, a separate Phonetic Planning Component to provide the quantitative target specifications for the utterance, and a Motor-Sensory Implementation Component to track and adjust the movements required to reach those targets on time. It preserves the insights of a symbol-based phonology, while also providing a comprehensive account of systematic phonetic variation, including timing.

A sketch of a Phonology-Extrinsic-Timing-Based Three-Component model of speech production

This chapter presents the outline of a model of speech-production planning, based on symbolic phonology and the specification of surface-timing patterns using general-purpose timekeeping mechanisms. This phonology-extrinsic-timing-based, three-component (XT/3C) model includes a Phonological Planning Component, to set and prioritize the goals for an utterance; a Phonetic Planning Component, to quantitatively specify the acoustic targets and the movements to achieve them; and a Motor-Sensory Implementation component, to track the planned movements and adjust them to ensure that the targets are reached on time. This approach addresses some of the gaps in earlier speech-production models based on abstract symbolic phonology, by proposing a mechanism for the specification of context-appropriate surface phonetic variation, including timing. In this way it provides an alternative to the Task-Dynamics-based approach embodied in Articulatory Phonology.

Evidence for an alternative approach to speech production, with three model components

Evidence presented in previous chapters suggests consideration of an alternative to the coupled-oscillator approach to modeling human speech planning and production processes. One alternative approach is based on the symbolic phonemic representations of Generative Phonology. This approach requires a separate mechanism to translate these symbolic representations into the quantitative context-appropriate specifications that can produce the surface form of an utterance. To date models of this type have not included comprehensive versions of components that complete this symbol-to-quantification translation process. This chapter reviews the evidence that supports a three-component model of this process, with an abstract symbolic Phonological Planning Component to specify the goals of the utterance at the level of contrastive feature cues; a Phonetic Planning Component to translate these goals into acoustic targets with their articulatory realizations; and a Motor-Sensory Implementation Component to track and adjust the articulatory movements which create the vocal-tract configurations that realize these goals. Development of such a three-component model would allow direct comparison with performance of the oscillator-based AP/TD model.

Neuromotor Organization of Speech Production

The production of speech is a multistep process requiring close coordination between neurolinguistic, neurocognitive, and neuromotor processes to communicate fluently and seemingly effortlessly. This complex process, which combines speech-specific and domain-general neural mechanisms, involves a closed repertoire of motor programs to control over 100 muscles distributed over the face, neck, and abdomen. The process requires neuromotor mechanisms to implement phonological planning, response selection, sequencing, and timing, contextual adjustments of the motor programs, as well as action execution and response monitoring. Recent advances in neuroimaging and neuromodulation techniques have led to the emergence of neurobiologically realistic models of speech production, leading to more comprehensive understanding of the mechanisms involved in producing speech. This chapter reviews the most up-to-date knowledge on the neural organization of the brain systems involved in producing speech.