The Motor Somatotopy of Speech Perception

Abstract

Listening to speech recruits a network of fronto-temporo-parietal cortical areas. Classical models consider anterior (motor) sites to be involved in speech production whereas posterior sites are considered to be involved in comprehension. This functional segregation is challenged by action-perception theories suggesting that brain circuits for speech articulation and speech perception are functionally dependent. Although recent data show that speech listening elicits motor activities analogous to production, it's still debated whether motor circuits play a causal contribution to the perception of speech. Here we administered transcranial magnetic stimulation (TMS) to motor cortex controlling lips and tongue during the discrimination of lip- and tongue-articulated phonemes. We found a neurofunctional double dissociation in speech sound discrimination, supporting the idea that motor structures provide a specific functional contribution to the perception of speech sounds. Moreover, our findings show a fine-grained motor somatotopy for speech comprehension. We discuss our results in light of a modified "motor theory of speech perception" according to which speech comprehension is grounded in motor circuits not exclusively involved in speech production.

Inside Speech: Multisensory and Modality-specific Processing of Tongue and Lip Speech Actions

“…These motor and premotor activations are in accordance with previous studies on auditory, visual, and audiovisual speech perception showing a key role of motor regions in speech processing (e.g., d'Ausilio et al, 2009d'Ausilio et al, , 2011Sato et al, 2009Sato et al, , 2010Möttönen & Watkins, 2009;Meister et al, 2007;Skipper et al, 2005Skipper et al, , 2007Pekkola et al, 2006;Pulvermuller et al, 2006;Wilson & Iacoboni, 2006;Ojanen et al, 2005;Callan et al, 2003Callan et al, , 2004Watkins & Paus, 2004;Wilson et al, 2004;Calvert & Campbell, 2003;Watkins et al, 2003;Campbell et al, 2001;Calvert et al, 2000). It is worthwhile noting that, in this study, participants were only asked to attentively listen to and/or watch speech stimuli.…”

“…Brain areas involved in the planning and execution of speech actions (i.e., the posterior part of the left inferior frontal gyrus, the premotor and primary motor cortices) have indeed shown neural responses during auditory speech perception (e.g., Pulvermuller et al, 2006;Wilson & Iacoboni, 2006;Wilson, Saygin, Sereno, & Iacoboni, 2004). In addition, repetitive and double-pulse TMS studies also suggest that speech motor regions are causally recruited during auditory speech categorization, especially in case of complex situations (e.g., the perception of acoustically ambiguous syllables or when phonological segmentation or working memory processes are strongly required; d'Ausilio, Bufalari, Salmas, & Fadiga, 2011;d'Ausilio et al, 2009;Möttönen & Watkins, 2009;Sato, Tremblay, & Gracco, 2009;Meister, Wilson, Deblieck, Wu, & Iacoboni, 2007). Taken together, these results support the idea that our motor knowledge used to produce speech sounds helps to partly constraint phonetic decoding of the sensory inputs, as proposed in motor and sensorimotor theories of speech perception and language comprehension (Pickering & Garrod, 2013;Schwartz, Ménard, Basirat, & Sato, 2012;Skipper, Van Wassenhove, Nussman, & Small, 2007;Liberman & Mattingly, 1985).…”

Interaction between auditory and motor systems in speech perception

“…For example, in a speech perception task, strong activation in the motor cortex can be induced only when participants perceive the target speech [24,31] . Some studies using TMS of the motor cortex have demonstrated that stimulation of speech-related regions affects speech perception [32][33][34] . For example, using TMS to suppress the left premotor cortex, which is activated both during speech production and speech perception (Fig.…”

Knowing beans: human mirror mechanisms revealed through motor adaptation

“…In this case, the operation of MMs is inferred when activity in a particular cortical area (as reflected in the BOLD signal) is similar during action recognition and action production, and when the cortical area is a likely homolog of an area in macaque cortex in which mirror neurons have been identified. Using this or a similar logic, it appears that the human MMs respond more to actions that the perceiver can perform than to actions the perceiver is familiar with through vision alone (Calvo-Merino et al, 2006); MMs are more sensitive to social actions than similar non-social actions (Kilner et al, 2006); MMs respond to both visually perceived actions and the linguistic description of actions (Tettamanti et al, 2005); MMs play a role in speech perception (D'Ausilio et al, 2009); activity in MMs is positively correlated with empathy (Gazzola et al, 2006) and negatively correlated with autistic behaviors (Dapretto et al, 2006). …”