Models and Theories of Speech Production

Spoken language is conveyed via well-coordinated speech movements, which act as coherent units of control referred to as gestures. These gestures and their underlying movements show several distinctive features. However, currently, no existing theory successfully accounts for all properties of these movements. Even though models in speech motor control in the last forty years have consistently taken inspiration from general movement science, some of the comparisons remain ill-informed. For example, our present knowledge on whether widely known principles that apply to limb movements (e.g., the speed-accuracy trade off known as Fitts’ law) also hold true for speech movements is still very limited. An understanding of the principles that apply to speech movements is key to defining the somewhat elusive concept of speech motor skill and to assessing and interpreting different levels of that skill in populations with and without diagnosed speech disorders. The latter issue taps into fundamental debates about whether speech pathology assessment paradigms need to be restricted to control regimes that are specific to those underlying regular speech production. Resolution of such debates crucially relies on our understanding of the nature of speech processes and the underlying control units.

Unlike movements in locomotion or oculomotor function, speech movements when combined into gestures are not mere physical instantiations of organs moving in space and time but, also, have intrinsic symbolic function. Language-particular systems, or phonological grammars, are involved in the patterning of these gestures. These regulate the permissible symbolic combinations as evidenced via eliciting judgments on whether any given sequence is well-formed in any particular language (the same sequence can be acceptable in one, but not the other language). In what ways these contraints shape speech gestures and how these fit with existing general principles of motor control is, also, not clearly understood.

However, speech gestures are parts of words and thus one window into understanding the nature of the speech production system is to observe speech movements as parts of words or larger chunks of speech such as phrases or sentences. The intention to produce a lexical item involves activating sequences of gestures that are part of the lexical item. The regulation in time of the units in such sequences raises major questions for speech motor control theories (but also for theories of cognition and sequential action in general). Major challenges are met in the inter-dependence among different time scales related to gestural planning, movement execution and coordination within and across domains of individual lexical items. How these different time scales interact and how their interaction affects the observed movement properties are not well understood.

We welcome theoretical and empirical contributions which explore the nature of the dynamics of speech motor control at different time scales, separately or in combination. The theoretical papers can be part of existing models but need to add new insights and/or data. Empirical papers that relate to disordered speech and /or language processes are welcome, provided they also address important theoretical notions which sharpen an existing or develop a new theoretical perspective on speech production.