Poster E32, Thursday, August 22, 2019, 3:45 – 5:30 pm, Restaurant Hall
Discourse belief-updating in the right hemisphere
Maxime Tulling1, Ryan Law2, Ailís Cournane1, Liina Pylkkänen1,2;1New York University, 2NYU Abu Dhabi Research Institute
Introduction: With language, we can describe either the actual world or possible worlds. Little is known about the neurobiological basis of this contrast. Here we studied it by comparing the processing of factual assertions, which are claims about the world under discussion that allow you to update your beliefs about this world accordingly (e.g. ‘John loves Mary’), and expressions involving the modal verbs ‘may’ and ‘must’, which refer to possible states of affairs that are not actual or known (e.g., ‘John must love Mary’). Methods: A magnetoencephalography (MEG) study (N=25) compared visually presented sentences (Rapid Serial Visual Presentation) containing the modals ‘may’ and ‘must’ against sentences containing the factual verb ‘do’. In order to have do naturally appear in the same position as may and must, our sentences contained VP ellipsis (…and the king knows that the squires do/may/must too), controlled for elided-VP length and complexity. The interpretation of the modals was further dependent on prior (pre-normed) contexts biasing towards either an inferential or permission/obligation reading, which served as another independent factor. Target sentences (N=240) were followed by a task sentence, where participants indicated whether these were natural continuations or not. Results: A spatiotemporal cluster based permutation test on the full-brain in the time window 100-900ms after target word onset revealed a significant cluster reflecting a robust increase for the factual conditions over the modal ones, at 210-350ms starting around the right Temporoparietal Junction (rTPJ) and spreading up to the right Inferior Parietal Sulcus (rIPS) and right medial surfaces (cuneus - posterior cingulate cortex). We did not observe any significant differences between the different types of modal verbs nor any reliable activity increases for modal verbs over factual verbs. Discussion: We hypothesize that this increased activation for the factual condition may reflect computations involved with evaluation and integration of claims made about the world of evaluation, a process absent from the modal condition as those sentences only contribute possible compatibilities with the evaluated world. This belief-updating function is in line with suggestions that the rTPJ plays a role in theory revision and conceptual change (Martin & McDonald, 2003; Corbetta et al., 2008; Mahy et al., 2014) and supports that the right hemisphere is involved in pragmatic processing and contextual coherence (Kuperberg et al., 2006; Virtue et al., 2006). Follow-up experiment: In a follow up experiment, we are contrasting the belief-updating hypothesis with several others. We presented stimuli without a third person character (… so the squires do/may/might too). Our results (n=15) show no effect of our manipulation in right temporal and parietal areas ~100-500ms. For comparison, a random sample of 15 participants from the original study with the same test criteria showed a strong trending spatio-temporal cluster. This suggests the activity observed in the rTPJ might reflect updating the representation of someone else’s beliefs. This is consistent with studies relating rTPJ activity to theory of mind and reasoning about other minds (Saxe & Wexler, 2005).
Themes: Meaning: Discourse and Pragmatics, Meaning: Lexical Semantics
Method: Electrophysiology (MEG/EEG/ECOG)