Two complementary mechanisms for decoding intentions in speech intonation
There is much more to human communication than the (de)coding of the explicit, propositional meaning of a vocal speech signal. Between the lines, the vocal output reveals a lot about the speakers’ beliefs, attitudes and communicative intentions. Much of such implicit, illocutionary meaning is conveyed by the “manner of saying”, i.e. the speech prosody, and the interpretation of those subtleties involves a lot of pragmatic inference. There is growing evidence that this latter faculty is distinct from our language abilities such as phonology, syntax and semantics (Levinson, 2000), making it reasonable to assume the involvement of brain areas beyond the well-known left-dominant fronto-temporal language network in human vocal communication. In the first half of the talk, I will present a neuroimaging study that investigates the neural bases of decoding communicative intentions conveyed by prosodic contour (i.e. by manipulating HOW something is said; henceforth termed pragmatic meaning) in contrast to the decoding of lexical meaning (i.e. by manipulating WHAT is said). The brain data suggest two complementary mechanisms to decode intentions in speech intonation: First, we found evidence for inferential mechanisms involving the “mentalizing area” in medial prefrontal cortex, known to support the inference of others’ mental states and the decoding of their intentions in social scenarios (Amodio et al., 2006). Second, we found evidence for motor-simulation mechanisms involving the “larynx area” in the right hemisphere (Brown et al., 2008) that possibly mirrors motor programs for the production of different pitch contours and thus aids speech comprehension (D’Ausilio et al., 2011). In the second half of the talk, I will present novel results on the connectivity within the “prosody network” in the human brain. Converging evidence from two experiments points to a dorsal fiber tract in the right hemisphere as the most likely substrate for the transfer of prosodic information between brain areas. In conclusion, the present talk aims to complement traditional language models by demonstrating that the “more” in human communication embraces two well known neural mechanisms of human social interaction and involves pathways that are hemispheric homologues to those reported in the conventional language literature.