PACT Theory

We have settled in the last ten years a new theoretical framework, the “Perception-for-Action-Control Theory (PACT)”, which connects in a principled way perceptual shaping and motor procedural knowledge in speech multisensory processing in the human brain (Schwartz et al., 2007, 2012a). The Perception-for-Action-Control Theory considers that speech perception is the set of mechanisms that enable not only the listener to understand, but also the speaker to control speech in a communicative process.
In PACT, it is acknowledged that perception and action are co-structured in the course of speech development, which involves both producing and perceiving speech items. In consequence, the perceptual system is intrinsically organised in reference to speech gestures, and in relation with the structure of the action system. This is how PACT includes, in one way or another, an implicit “procedural knowledge of speech production”. Conversely, perception provides action with auditory (and possibly visual) templates, which contribute to define the gesture, specifying control principles, organisation schemes and functional values. This is how PACT incorporates “gesture perceptual shaping’’. In PACT, the communication unit, through which parity may be achieved, is neither a sound, nor a gesture, but a perceptually-shaped gesture, that is a perceptuo-motor unit. It is characterised by both its articulatory coherence – provided by its gestural nature – and its perceptual value – necessary for being functional.
PACT considers two roles for the perceptuo-motor link during speech perception (see Figure). The “offline co-structuration hypothesis” assumes co-structuring of perceptual and motor representations in the course of speech development, enabling auditory categorization mechanisms to take motor information into account (dotted line in Figure). While it seems clear that auditory categorisation processes exist and develop earlier than speech production knowledge in ontogeny, the further development of motor procedural knowledge would, in PACT, modify and possibly enhance the perceptual repertoire. It is also at this level that subtle online transient modifications of motor or auditory repertories could take place in various kinds of adaptation paradigms or motor resonance phenomena.
The “online perceptuo-motor binding hypothesis” considers online influence of motor knowledge on auditory or multisensory speech processing for the extraction and characterization of relevant cues (solid lines in Figure). The role of the motor system would be particularly important in noise, adverse or complex communication conditions, and it would possibly intervene in the speech segmentation process.
In neuroanatomical terms, the two hypotheses are associated with the perceptuo-motor connection in the dorsal route. Considering “offline co-structuration”, perceptual representations in the temporal pole would be structured in relationship with motor representations in the parieto-frontal pole in the course of speech development, and later on, all along life, through dynamic adaptations in various learning conditions. Considering “online perceptuo-motor binding”, comprehension would operate basically in the temporal pole within the ventral route, but the motor system would be involved online through the dorsal route – increasingly in various kinds of adverse conditions – to assist speech scene analysis and improve and enhance the extraction of auditory and visual cues.

Schwartz, J.L., Abry, C., Boë, L.J., & Cathiard, M. (2002). Phonology in a theory of perception-for-action-control. In J. Durand, B. Laks (eds.) Phonology : from Phonetics to Cognition (pp. 255-280). Oxford: Oxford University Press.
Schwartz, J.L., Boë, L.J., & Abry, C. (2007). Linking the Dispersion-Focalization Theory (DFT) and the Maximum Utilization of the Available Distinctive Features (MUAF) principle in a Perception-for-Action-Control Theory (PACT). In M.J. Solé, P. Beddor & M. Ohala (eds.) Experimental Approaches to Phonology (pp. 104-124). Oxford University Press.
Schwartz, J.L., Basirat, A., Ménard, L., & Sato, M. (2012). The Perception for Action Control Theory (PACT): a perceptuo-motor theory of speech perception. Journal of NeuroLinguistics, 25, 336-354.