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Identifying the neural bases of phonological learning
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Poster A42 in Poster Session A, Tuesday, October 24, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
This poster is part of the Sandbox Series.
Chiara Repetti-Ludlow1, Adam Buchwald1; 1New York University
Past research has shown that targeting the left motor cortex (M1) with transcranial direct current stimulation (tDCS) during a speech motor learning task can enhance learning of novel speech sound sequences, such as onset consonant clusters (Buchwald et al., 2019). This mirrors similar findings in non-speech motor learning, where targeting M1 can enhance learning in both unimpaired speakers and stroke survivors. However, learning in the speech domain includes both motor learning and phonological (more abstract) learning. Thus, while targeting M1 can enhance motor learning, it remains possible that additional regions are relevant for phonological learning. This sandbox series research project addresses this issue by comparing performance on a phonological learning task while using tDCS to target regions associated with motor (M1) and phonological (pars opercularis) processing. Data collection is beginning, with one group receiving anodal stimulation over M1 (C3 in the 10-20 system), a second group receiving anodal stimulation over LIFG (F5), and a third group receiving sham stimulation. In all cases, the cathode is over the right supraorbital region (Fp2). 20 participants will be recruited for each of the three groups. In order to limit motor effects in this study, we have designed a phonological learning task in an artificial grammar paradigm. Participants learn words in an “alien language” that contains “back vowel harmony,” in which two vowels in the same word assimilate to have the same backness. This process is well-attested in the world’s languages (Rose & Walker, 2011), and previous work has shown that adults who do not speak a language with vowel harmony can still acquire harmony patterns within 20 minutes (Finley, 2017). In the training phase, participants see images with three animals and a circle around one, two, or all three animals. Animal names are phonotactically-legal nonwords. In one version, two animals have a dual suffix “-a,” and three animals have a plural suffix “-u.” Thus, if one animal is called leeg, then two are leega, and three are lugu, with the first vowel moving back and rounding in accordance with the phonological process. After a 20-minute phonological training phase that coincides with the tDCS administration, participants are presented with previously untested images. They hear recordings of two words and then select which they think correctly describes the image. Critical trials will compare items that follow the phonological process with those that don’t (in this example, lugu vs. leegu). Pilot testing done without stimulation indicate that there is not a ceiling effect, thus allowing for different magnitudes of improvement. We hypothesize that the participants in the active tDCS LIFG group will perform significantly better than others at learning the back vowel harmony phonological process. These findings will be compared to our ongoing work on novel consonant cluster learning targeting the same regions. Results from this study will shed new light on our understanding of the neural architecture underlying phonetic and phonological learning processes.
Topic Areas: Phonology, Speech Motor Control