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Poster B1, Wednesday, November 8, 3:00 – 4:15 pm, Harborview and Loch Raven Ballrooms

The role of individual differences in inhibition on sentence choice during speech

Malathi Thothathiri1, Daniel Evans1;1The George Washington University

Language contains multiple structural options for expressing meaning (e.g., double-object dative (DO): Mark gave Laura the pen, prepositional-object dative (PO): Mark gave the pen to Laura). How do speakers choose between such competing options during sentence production? We hypothesized a role for exposure to different structures and individual differences in inhibition. We report behavioral and neuroimaging studies that tested these hypotheses and elucidated the neurocognitive mechanisms supporting choice during speech. The studies used a training and subsequent production paradigm that allowed us to manipulate language exposure within the lab. During training, participants watched puppet-enacted transfer actions, heard DO and PO datives, and repeated the sentences (e.g., Kate gave the tiger the cup). Ten dative verbs appeared twelve times each. Four verbs appeared only in DO (DO-only), four only in PO (PO-only), and two equally in the two structures (Equal-DO-PO). Assignment of verbs to exposure conditions was counterbalanced across lists. Subsequent to training, participants described new videos using dative sentences of their choice. The test videos contained different animals and objects than training. Eighty-eight participants completed the behavioral study. During test, they produced fewer DO than PO sentences overall, consistent with a dispreferrence for the DO dative found in previous studies. We sought to identify factors that enabled the production of the dispreferred structure. The results revealed: (a) A significant linear effect of exposure condition on proportion DO produced (DO-only>Equal-DO-PO>PO-only). Thus, exposure to verbs in the DO structure increased DO production with those verbs. (b) A significant correlation between inhibition (as measured by Stroop) and DO production in the Equal-DO-PO but not the other conditions. Thus, individuals with better inhibition were more likely to produce the dispreferred structure, but especially so for verbs that appeared equally often in two competing structures during training, replicating a previous study [1]. Twenty-five participants completed the neuroimaging study. The scan occurred within 1-3 days after training. DO productions following a DO versus a PO were analyzed separately due to known syntactic priming effects from a previous trial. Producing DO after a PO (i.e., changing from a primed structure) showed widespread activation that was positively correlated with Stroop performance. Individuals with better inhibition showed greater activation than those with poorer inhibition in medial and lateral frontal regions associated with executive function. Activation during DO production overlapped with activation during Stroop in the anterior cingulate cortex (ACC) only. Splitting by exposure condition, ACC activation showed a significant linear trend (DO-only<Equal-DO-PO<PO-only). Thus, the strongest activation was associated with producing DO structures with verbs that had only appeared in PO (and thereby involved overriding previous exposure). This overriding appeared to be costly, however. Individuals showing strong ACC activation for DO production with PO-only verbs produced significantly fewer DO structures with those verbs. To summarize, individual differences in inhibition interacted with statistical properties of language exposure to determine how often speakers produced dispreferred versus preferred structures. Our novel behavioral and neuroimaging paradigm yielded mechanistic insights into how structural choices are made during speech. [1] Thothathiri & Rattinger (2015), PNAS.

Topic Area: Control, Selection, and Executive Processes

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