Figure 4. An integrated state feedback control (SFC) model of speech production.

Speech models derived from the feedback control, psycholinguistic, and neurolinguistic literatures are integrated into one framework, presented here. The architecture is fundamentally that of a SFC system with a controller, or set of controllers (Haruno et al., 2001), localized to primary motor cortex, which generates motor commands to the vocal tract and sends a corollary discharge to an internal model which makes forward predictions about both the dynamic state of the vocal tract and about the sensory consequences of those states. Deviations between predicted auditory states and the intended targets or actual sensory feedback generates an error signal that is used to correct and update the internal model of the vocal tract. The internal model of the vocal tract is instantiated as a “motor phonological system”, which corresponds to the neurolinguistically elucidated phonological output lexicon, and is localized to premotor cortex. Auditory targets and forward predictions of sensory consequences are encoded in the same network, namely the “auditory phonological system”, which corresponds to the neurolinguistically elucidated phonological input lexicon, and is localized to the STG/STS. Motor and auditory phonological systems are linked via an auditory-motor translation system, localized to area Spt. The system is activated via parallel inputs from the lexical-conceptual system to the motor and auditory phonological systems.