Poster D40, Wednesday, August 21, 2019, 5:15 – 7:00 pm, Restaurant Hall
Dynamic updating of native syntax
Malathi Thothathiri1, Kelly Sharer1;1The George Washington University
Background: Recent results suggest that native syntax learning is life-long and not restricted to childhood. Adults update sentence production and comprehension based on the statistical properties of new input. Prediction-and-error-based learning has been posited as a likely mechanism: specifically, that during language perception, the parser predicts how a sentence is going to unfold and updates the language system based on match or mismatch between the predicted and actual structures. Hypotheses: We hypothesized that (1) such learning might utilize frontal cortex based cognitive control mechanisms that can detect and resolve mismatch between expected and actual outcomes; and (2) the recruitment of these regions would vary according to (2a) individual differences in cognitive control and (2b) the statistical associations between verbs and sentence structures. Methods: In multiple studies using different sentence structures, we exposed participants to native language (English) input that manipulated which verbs were experienced in which structures, and investigated the neural substrates of subsequent naturalistic comprehension and production using functional MRI. Based on prior findings, we focused on two well-known control regions—the anterior cingulate cortex (ACC) and the left inferior frontal cortex (LIFC). Individual differences in cognitive control were measured using Stroop. The production study examined a common syntactic alternation in English between double-object (DO) and prepositional-object (PO) datives (Mika gave Joan the pencil vs. Mika gave the pencil to Joan). Participants heard some English verbs only in DO, some only in PO, and others equally in both. Subsequently, they described new events using structures of their own choice. The comprehension study examined a commonly studied syntactic ambiguity in English between main-verb (MV) and relative-clause (RC) interpretations (The soldiers warned about the dangers… before the raid vs. …conducted the raid). Participants read MV and RC sentences and indicated reading completion and answered periodic comprehension questions. Results: Behavioral results confirmed that adults adjust production and comprehension based on new input (not discussed). Neurally, for production, (1) ACC and LIFC were recruited; and (2) recruitment for producing the less common structure (DO) varied with (2a) individual differences in Stroop, with better performers showing greater activation and (2b) a verb’s statistical associations, with the highest ACC activation for producing verbs in the statistically un-associated structure. For comprehension, (1) LIFC was recruited when reading the less common structure (RC) and this recruitment decreased as participants received more exposure; and (2) the decrease in LIFC activation varied with (2a) individual differences in Stroop, with better performers showing a greater decrease and (2b) a verb’s statistical associations, with quicker adaptation for verbs that led to the greatest mismatch (i.e., prediction-error). Conclusions: These studies reveal new insights about how adults dynamically update their native language. Frontal cognitive control regions help integrate new language input with expectations from prior language experience, with potentially different regions used at the response (motor production, ACC) versus representational (LIFC) levels. The neural substrates of updating also vary according to an individual’s cognitive control abilities and a particular verb’s statistical associations, suggesting flexible weighting of different brain regions during sentence processing.
Themes: Syntax, Control, Selection, and Executive Processes
Method: Functional Imaging