Poster B37, Tuesday, August 20, 2019, 3:15 – 5:00 pm, Restaurant Hall
Decoding linguistic communications in human premotor cortex
Wenshuo Chang1, Lihui Wang2, Xiaolin Zhou1;1Peking University, 2Otto-von-Guericke University, Magdeburg, Germany
Language using has been proposed as a type of communicative action (i.e., speech acts, Austin, 1955; Searle, 1969) which serves the function of achieving the speaker’s goal, rather than merely making a statement that can be proved true or false. In daily conversations, for example, we ask and answer questions, and make requests and promises. Here we test whether linguistic communications are represented as actions by decoding speech acts in human premotor cortex, a brain area known for action preparation and simulation. In an fMRI experiment, participants were presented with scripts describing a daily-life scenario, each of which consisted of an event concerning two interlocutors (a speaker and an addressee) and a critical sentence said by the speaker. This critical sentence was either a promise, a request, or an answer to a confirmative question that was included as the control for the promise (Answer 1) or the request (Answer 2). After fMRI scanning, participants were asked to rate the degree to which the event would be favored by the speaker (i.e., speaker-favor) and the addressee (addressee-favor). The multivariate pattern analysis (MVPA) revealed that the speech acts (Promise vs. Answer 1, Request vs. Answer 1, Promise vs. Request) can be discriminated not only by the voxel patterns in left inferior frontal gyrus (LIFG) and left middle temporal gyrus (LMTG), the brain areas known for semantic processing, but also by voxel patterns in dorsal and ventral premotor cortex. The discrimination, in terms of classification accuracies of the MVPA classifier, was specific to speech acts (only in pair-wise classifications involved Promise or Request), but was not observed for confirmative answers (Answer 1 vs. Answer 2). Moreover, the discriminative performance was better in premotor cortex than in LIFG and LMTG. Further representational similarity analysis (RSA) showed that, for voxels in LIFG and LMTG, the pattern similarity between Promise and Answer 1 can be accounted for only by ratings on addressee-favor but not by ratings on speaker-favor, whereas the pattern similarity between Request and Answer 2 can be accounted for only by ratings on speaker-favor but not by ratings on addressee-favor. The same pattern of results was observed for voxels in premotor cortex, except that the pattern similarity between Request and Answer 2 can be accounted for by both ratings on speaker-favor and ratings on addressee-favor. The RSA results suggested that the voxel patterns in these areas can be predicted by the degree to which the action is in favor of the interlocutors, and premotor cortex tended to represent more action-related information than LIFG and LMTG. Taken together, the current study demonstrates the role of premotor cortex in representing and understanding speech acts.
Themes: Meaning: Discourse and Pragmatics, Meaning: Combinatorial Semantics
Method: Functional Imaging