Understanding particularized and generalized conversational implicatures: Is theory-of-mind necessary?

A speaker's intended meaning can be inferred from an utterance with or without reference to its context for particularized implicature (PI) and/or generalized implicature (GI). Although previous studies have separately revealed the neural correlates of PI and GI comprehension, it remains controversial whether they share theory-of-mind (ToM) related inferential processes. Here we address this issue using functional MRI (fMRI) and transcranial direct current stimulation (tDCS). Participants listened to single-turn dialogues where the reply was indirect with either PI or GI or was direct for control conditions (i.e., PIC and GIC). Results showed that PI and GI comprehension shared the multivariate fMRI patterns of language processing; in contrast, the ToM-related pattern was only elicited by PI comprehension, either at the whole-brain level or within dorsal medial prefrontal cortex (dmPFC). Moreover, stimulating right TPJ exclusively affected PI comprehension. These findings suggest that understanding PI, but not GI, requires ToM-related inferential processes.