The model also incorporates both external and internal feedback loops as in the SFC framework and in Levelt’s psycholinguistic model (Levelt, 1983). In the context of a SFC framework, two kinds of internal forward models are maintained, one that makes forward predictions regarding

the state of the motor effectors and one that makes forward predictions regarding the sensory consequences of these motor effector states (Wolpert et al., 1995). Deviations between Fulvestrant cell line the predicted sensory consequences and the sensory targets generate an error signal that can be used to update the internal motor model and provide corrective feedback to the controller. We suggest that neuronal ensembles coding learned motor sequences, such as those stored in the hypothesized “motor phonological system,” form an internal forward model of the vocal tract in the sense that activation of a code for a speech sequence, say that for articulating the word cat, instantiates a prediction of future states of the vocal tract, namely those corresponding to the articulation of that particular sequence of sounds. Thus, activation of the high-level motor ensemble coding for the word cat drives the execution

of that sequence in the controller. Corollary discharge from the motor controller back to the higher-level motor phonological system can provide Ipatasertib purchase information (predictions) about where in the sequence of movements the vocal tract is at a given time point. Alternatively, or perhaps in conjunction, lower levels of the motor system, such as a frontocerebellar circuit, may fill in the details of where the vocal tract is in the predicted sequence given the particulars of the articulation, taking into account velocities, fatigue, etc. A hierarchically organized feedback

control system, with internal models and feedback loops operating at different grains of analysis, is in line with recent hypotheses ( Grafton et al., 2009, Grafton and Hamilton, 2007 and Krigolson and Holroyd, 2007) and makes sense in the context of speech where the motor system must hit sensory targets corresponding to features (formant frequency), before sound categories (phonemes), sequences of sound categories (syllables/words), and even phrasal structures (syntax) ( Levelt, 1983). Given that the concepts of sensory hierarchies and motor hierarchies are both firmly established, the idea of sensorimotor hierarchies would seem to follow ( Fuster, 1995). Thus while we discuss this system at a fairly course grain of analysis, the phonological level, we are open to the possibility that both finer-grained and more coarse-grained SFC systems exist.