The neural development of pragmatic inference-making in natural discourse

Older interlocutors are more likely than younger ones to make pragmatic inferences, that is, inferences that go beyond the linguistically encoded meaning of a sentence. Here we ask whether pragmatic development is associated with increased activity in brain structures associated with inference-making or in those associated with Theory of Mind. We employed a reading task that presents vignettes in one of two versions, one of which is expected to prompt more pragmatic processing. Both versions present a major premise containing three possibilities (e.g., Xavier is considering Thursday, Friday or Saturday for inviting his girlfriend out). In the Fully-Deductive (control) condition, the major premise is followed by two disjunction-elimination premises through two separate lines (one indicating that Saturday is not convenient and another saying that Thursday is not convenient); this is followed by a valid conclusion (e.g., "I'll reserve Friday"). In the Implicated-Premise condition, the first disjunction-elimination premise is followed by a second similar one that eliminates the same disjunction (e.g., both lines explain why Saturday is not convenient). In this condition, readers may pragmatically enrich the conclusion (i.e., "I'll reserve Friday" pragmatically implicates that Xavier is also eliminating Thursday from consideration). Reading times in Experiment 1 showed that processing the speaker's conclusion in the Implicated-Premise condition becomes increasingly more effort-demanding as readers reach adolescence. Experiment 2 showed that this developmental pattern is related to age-related increases in fMRI activity in fronto-parietal regions typically involved in inference-making processes. We found no evidence indicating age effects related to Theory of Mind areas.