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Transcranial Direct Current Stimulation of the Superior Parietal Cortex Modulates Reference Processing
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Poster C12 in Poster Session C, Wednesday, October 25, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Sarah C. Wilson1, Samantha Langley1, Kalil Warren1, Dirk B. den Ouden1, Amit Almor1; 1University of South Carolina, Columbia, SC USA
Introduction. Reference tracking is the ability to keep up with who/what is being referred to across sentences. The repeated name penalty (RNP) is the cognitive processing delay caused by the use of a repeated name in situations where a pronoun would suffice (Gordon et al., 1993). For example, sentences with repeated names (e.g., Bill) are read slower than sentences with a pronoun (e.g., he) when referring to a previously mentioned salient referent (Almor & Nair, 2007; Gordon et al., 1993). MRI studies found that the RNP is associated with bilateral activation in the superior parietal cortex (SPC), a brain region recruited for spatial tracking of visual stimuli (Almor et al., 2009; Conder et al., 2017). This suggests that the SPC is involved in consolidating multiple linguistic references. However, models of sentence processing rarely include these parietal regions, highlighting instead the left inferior frontal gyrus (IFG) as a core node in the syntactic network (e.g., Den Ouden et al., 2012). To test whether either area plays a causal role in the RNP, the present study compared the effects of cathodal high-definition transcranial direct current stimulation (HD-tDCS) of the left IFG and bilateral SPC on the RNP. Method. 85 students participated; 14 were excluded due to missing data or self-reported absence of stimulation sensation. All were right-handed native English speakers with normal/corrected-to-normal vision and no language disorders. The study had a 2x2x2x3 factorial design, with three within-participant factors: block (stimulation, post-stimulation), reference form (name, pronoun) and antecedent salience (salient, non-salient); and one between-participant factor: stimulation type (IFG, SPC, Sham). In the IFG and SPC conditions, stimulation of -2 milliamps was applied for 20 minutes; in Sham, stimulation only occurred during the first and final minute. The reading task included 96 three-sentence discourses followed by comprehension questions. Half of the critical trials were completed while receiving stimulation (stimulation block); the remaining critical trials followed stimulation (post-stimulation block). Results. Log transformed reading times of critical sentences were analyzed using linear mixed-effects models. There was a 3-way interaction for block, reference form, and salience approaching significance, β=.01, SE=.005, t=1.948, p=.052, suggesting that the RNP was modulated by stimulation. Post-hoc comparisons further revealed that stimulation affected the RNP only in the SPC condition, X2(1)=4.14, p=.042, but not in the IFG and Sham conditions, p’s>.65. Conclusion. Application of cathodal HD-tDCS to the bilateral SPC region modulated the RNP. No such effects were found for the IFG or Sham conditions. These results show, for the first time, that SPC plays a causal role in processing reference form during reference tracking in discourse. As such, these results support previous theories that were so far only supported by imaging results which do not necessarily implicate causality (Boiteau et al., 2017; Conder et al., 2017). Models of language comprehension that address discourse should include the parietal region as central to reference processing. Example stimuli: Ed moved into an apartment with Brooke. He brought most of the furniture. Ed / Brooke / He / She liked having a roommate to help out.
Topic Areas: Meaning: Discourse and Pragmatics, Reading