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Is the rTPJ necessary for processing indirectness and/or change of communicative function? A TMS study
Poster A5 in Poster Session A, Thursday, October 6, 10:15 am - 12:00 pm EDT, Millennium Hall
Isabella Boux1,2,3, Friedemann Pulvermüller1,2,3,4; 1Brain Language Laboratory, Freie Universitaet Berlin, 2Einstein Center for Neurosciences, Charite Universitaetsmedizin, Berlin, 3Berlin School of Mind and Brain, Humboldt Universitaet zu Berlin, 4Cluster of Excellence Matters of Activity, Humboldt Universitaet zu Berlin
In communication, information can be conveyed indirectly. For instance, when asked by A “Are you bringing your cat to the vet?” a person B could reply “It got hurt jumping down the table”. The reply would then implicate that, the cat is being brought to the vet (indirect speech acts, ISAs). In order to understand implicated messages, the listener needs to infer mental states or beliefs of the speaker, as well as assumptions shared between A and B (Common Ground or Theory of Mind, ToM). In particular, when B replies “It got hurt jumping down the table“, both A and B would typically assume that getting hurt jumping down a table can motivate a vet visit, and they would even assume that the respective other makes this assumption too. Several neuroimaging studies indicate that those cortical areas active during non-language ToM processing – most notably the right temporo-parietal junction, rTPJ (Schurz et al., 2022) – also become active when indirect speech acts are being understood (Basnakova et al., 2014; 2015; Feng et al., 2017; 2021), which is open to the interpretation that high ToM processing load is a critical feature of indirectness. However, previous studies compared conditions in which indirectness was not the only feature distinguishing between the critical indirect speech act condition and the direct control. Instead, indirectness was accompanied by a change in speech act function. Therefore, it is not clear whether the rTPJ is relevant for indirectness processing per se or rather for the processing of changes in communicative function, or possibly both. In the present study, we disrupt activity in the rTPJ during ISAs understanding and asses the effects on the comprehension of ISAs with and without co-occurring communicative function change. We either altered activation in the ToM-relevant rTPJ by applying repetitive transcranial magnetic stimulation (TMS condition) or applied sham (placebo) stimulation. We find that, in absence of TMS stimulation, both types of indirect replies are understood more slowly compared to matched controls. Crucially, TMS to the rTPJ differently affected the two types of ISAs. Under the effect of TMS, RTs delays between ISAs and their matched direct controls remained unaltered when both speech acts conveyed the communicative function (assertion). However, the response time difference between direct and indirect speech acts was reduced by TMS when these speech acts also differed in their communicative function (assertion vs acceptance/refusal of an offer). As no TMS effect was found in the speech-act matched condition, our results are inconsistent with a causal role of rTPJ in the processing of indirectness per se. However, they support the role of this region in processing the communicative function change that co-occured with indirectness in most previous experimental studies. The rTPJ might possibly be necessary for assessing common ground or for processing the speakers’ mental states to determine the correct or re-process the communicative function of an the utterance. Our findings suggest that TMS to rTPJ affected processing communicative function and related common ground, rather than indirectness.
Topic Areas: Meaning: Lexical Semantics, Control, Selection, and Executive Processes