Action recognition has been found to rely not only on sensory brain areas but also partly on the observer's motor system. However, whether distinct auditory and visual experiences of an action modulate sensorimotor activity remains largely unknown. In the present sparse sampling fMRI study, we determined to which extent sensory and motor representations interact during the perception of tongue and lip speech actions. Tongue and lip speech actions were selected because tongue movements of our interlocutor are accessible via their impact on speech acoustics but not visible because of its position inside the vocal tract, whereas lip movements are both “audible” and visible. Participants were presented with auditory, visual, and audiovisual speech actions, with the visual inputs related to either a sagittal view of the tongue movements or a facial view of the lip movements of a speaker, previously recorded by an ultrasound imaging system and a video camera. Although the neural networks involved in visual visuolingual and visuofacial perception largely overlapped, stronger motor and somatosensory activations were observed during visuolingual perception. In contrast, stronger activity was found in auditory and visual cortices during visuofacial perception. Complementing these findings, activity in the left premotor cortex and in visual brain areas was found to correlate with visual recognition scores observed for visuolingual and visuofacial speech stimuli, respectively, whereas visual activity correlated with RTs for both stimuli. These results suggest that unimodal and multimodal processing of lip and tongue speech actions rely on common sensorimotor brain areas. They also suggest that visual processing of audible but not visible movements induces motor and visual mental simulation of the perceived actions to facilitate recognition and/or to learn the association between auditory and visual signals.

Studies of speech motor control suggest that articulatory and phonemic goals are defined in multidimensional motor, somatosensory, and auditory spaces. To test whether motor simulation might rely on sensory–motor coding common with those for motor execution, we used a repetition suppression (RS) paradigm while measuring neural activity with sparse sampling fMRI during repeated overt and covert orofacial and speech actions. RS refers to the phenomenon that repeated stimuli or motor acts lead to decreased activity in specific neural populations and are associated with enhanced adaptive learning related to the repeated stimulus attributes. Common suppressed neural responses were observed in motor and posterior parietal regions in the achievement of both repeated overt and covert orofacial and speech actions, including the left premotor cortex and inferior frontal gyrus, the superior parietal cortex and adjacent intraprietal sulcus, and the left IC and the SMA. Interestingly, reduced activity of the auditory cortex was observed during overt but not covert speech production, a finding likely reflecting a motor rather an auditory imagery strategy by the participants. By providing evidence for adaptive changes in premotor and associative somatosensory brain areas, the observed RS suggests online state coding of both orofacial and speech actions in somatosensory and motor spaces with and without motor behavior and sensory feedback.