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This study investigated whether transcutaneous auricular vagus nerve stimulation (taVNS) enhances reversal learning and augments noradrenergic biomarkers (i.e., pupil size, cortisol, and salivary alpha-amylase [sAA]). We also explored the effect of taVNS on respiratory rate and cardiac vagal activity (CVA). Seventy-one participants received stimulation of either the cymba concha (taVNS) or the earlobe (sham) of the left ear. After learning a series of cue-outcome associations, the stimulation was applied before and throughout a reversal phase in which cue-outcome associations were changed for some (reversal), but not for other (distractor) cues. Tonic pupil size, salivary cortisol, sAA, respiratory rate, and CVA were assessed at different time points. Contrary to our hypothesis, taVNS was not associated with an overall improvement in performance on the reversal task. Compared to sham, the taVNS group performed worse for distractor than reversal cues. taVNS did not increase tonic pupil size and sAA. Only post hoc analyses indicated that the cortisol decline was steeper in the sham compared to the taVNS group. Exploratory analyses showed that taVNS decreased respiratory rate but did not affect CVA. The weak and unexpected effects found in this study might relate to the lack of parameters optimization for taVNS and invite to further investigate the effect of taVNS on cortisol and respiratory rate.
According to the Shallow Structure Hypothesis (SSH), second language (L2) speakers, unlike native speakers, build shallow syntactic representations during sentence processing. In order to test the SSH, this study investigated the processing of a syntactic movement in both native speakers of English and proficient late L2 speakers of English using pupillometry to measure processing cost. Of particular interest were constructions where movement resulted in an intermediate gap between clauses. Pupil diameter was recorded during auditory presentation of complex syntactic constructions. Two factors were manipulated: syntactic movement (such that some conditions contained movement while others did not), as well as syntactic movement type (either causing an intermediate gap or not). Grammaticality judgments revealed no differences between the two groups, suggesting both were capable of comprehending these constructions. Pupil change slope measurements revealed a potential sensitivity to intermediate gaps for only native speakers, however, both native and late L2 speakers showed similar facilitation during processing of the second gap site. Acoustic analysis revealed potential acoustic cues that may have facilitated the processing of these constructions. This suggests that, contrary to the predictions of the SSH, late L2 speakers are capable of constructing rich syntactic representations during the processing of intermediate gap constructions in spoken language.
In a preferential looking paradigm, we studied how children's looking behavior and pupillary response were modulated by the degree of phonological mismatch between the correct label of a target referent and its manipulated form. We manipulated degree of mismatch by introducing one or more featural changes to the target label. Both looking behavior and pupillary response were sensitive to degree of mismatch, corroborating previous studies that found differential responses in one or the other measure. Using time-course analyses, we present for the first time results demonstrating full separability among conditions (detecting difference not only between one vs. more, but also between two and three featural changes). Furthermore, the correct labels and small featural changes were associated with stable target preference, while large featural changes were associated with oscillating looking behavior, suggesting significant shifts in looking preference over time. These findings further support and extend the notion that early words are represented in great detail, containing subphonemic information.