Mapping of functions to brain regions : A neuro-phonetic model of speech production, perception, and acquisition

A model has been computer-implemented which is capable of producing and/or perceiving speech items (sounds, syllables, words, or short utterances). The organization of the model is given in Fig. 1 (see also Kröger et al. 2009a). Its cognitive linguistic module is not modelled in detail in this neurophonetic approach but it can be assumed that this module is subdivided into a procedural and a declarative part (Ullman 2001). Here it is assumed that phonemic word forms are selected from a mental lexicon (Levelt 1992, Levelt et al. 1999, Indefrey & Levelt 2004) forming the main part of the declarative memory. These forms pass linguistic processing modules including the syllabification module (procedural memory and appropriate processing modules) and subsequently they build up a chain of phonemically specified speech items on the level of the phonemic map (Fig. 1). The subsequent part of the model is the phonetic or sensorimotor module. Within all parts of the model, a neural map is defined as an ensemble of neurons located in a specific brain region which can be associated with a distinct cognitive or sensorimotor representation or state of a speech item. Different neural activation patterns occurring within a neural map represent different neural states and different speech items. Coming back to the phonemic map, thus the phonemic description of each speech item generated by the cognitive linguistic module is coded by a distinct neural activation pattern or neural state within the phonemic map. Subsequently within the phonetic or sensorimotor module, speech production can be separated in sensorimotor feedforward and feedback control (cf. Guenther 2006 and Guenther et al. 2006). Feedforward control is the direct generation of articulatory movements from a specific phonemic state. Sensorimotor feedback control is activated during production in order to control, whether the phonetic realization of a speech item is correct and, if it is not, to correct its production.