This state estimate is transformed into a forward prediction of the acoustic consequences of the motor command. We also assume that a forward prediction of the somatosensory consequences of the motor command is generated, although we will not discuss the role of this system here. The forward auditory prediction, in turn, supports two functions as noted above. One is a rapid internal monitoring function, which calculates whether the current motor commands are likely to hit their intended sensory targets (this implies that the targets are known independently of the forward predictions, see below) and provides corrective feedback

if necessary. Needless to say, the usefulness of this internal feedback depends on how accurate the internal model/forward prediction is. Therefore it is important selleckchem to use actual sensory feedback to update and tune the internal model to ensure it is making accurate predictions. This is the second (slower, external monitoring) function of the forward predictions: to compare predicted with actual sensory consequences and use prediction error to generate a corrective

signal to update the internal model, which in turn provides input to the motor controller. Of course, if internal feedback monitoring fails to catch an error in time, external feedback can be used to correct movements as well. BI6727 As noted above, an internal feedback loop that generates a forward prediction of the sensory consequence of an action is useless if the intended most sensory target is not known. This raises an interesting issue because unlike in typical visuomanual paradigms where actions are often directed at external sensory targets, in most speech acts there is no immediate externally provided sensory target (unless one is repeating heard speech). Instead the sensory goal of a speech act is an internal representation (e.g., a sequence of speech sounds) called up from memory on the basis of a higher-level goal, namely, to express a concept via a word or phrase that corresponds

to that concept. This, in turn, implies that speech production involves the activation of not only motor speech representations but also internal representations of sensory speech targets that can be used to compare against both predicted and actual consequences of motor speech acts. Psycholinguistic models of speech production typically assume an architecture that is consistent with the idea that speech production involves the activation of a sensory target. For example, major stages of such models include the activation of a lexical-conceptual representation and access to the corresponding phonological representation followed by articulatory coding (Dell et al., 1997 and Levelt et al.