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Dopaminergic contributions to novel word learning
Poster Session B, Friday, October 25, 10:00 - 11:30 am, Great Hall 3 and 4
Peter Su1, David Copland1,2, Nadeeka Dissanayaka1,3, Anthony Angwin1; 1University of Queensland, 2STARS Education & Research Alliance, 3UQ Centre for Clinical Research
INTRODUCTION: Word learning occurs across the adult lifespan. It is a computationally complex process, drawing on language, executive, reward, and memory networks. Dopamine is crucial to the function of these networks, as both a neurotransmitter and a neuromodulator. While several studies have found that increasing dopamine availability in healthy adults facilitates contextual word learning, there remain open questions about how these findings translate to associative novel word learning. METHODS: Building on previous work, we investigated the effects of dopamine availability on word learning. Using a placebo-controlled, between groups study design, we examined the impact of levodopa VS placebo using an associative novel word learning task, in a group of healthy young adults (placebo n=18; levodopa n=17). The task drew on a stimulus set of 100 picture-word pairs, comprising audio recordings of novel words paired with either a familiar or unfamiliar object. Participants attended an intensive 4-day learning block, where they received levodopa or placebo prior to learning the picture-word pairs. They were assessed for learning via recognition and recall tasks on each day, with further delayed testing at 1 week and 4 weeks. We predicted that levodopa would improve novel word learning performance relative to placebo. Given the tight coupling of hippocampal reward loops with learning, we also predicted that successful word learning would be correlated to reward sensitivity. RESULTS: Analysis of the results revealed that participants receiving levodopa demonstrated higher overall recall accuracy as well as earlier acquisition during the learning block relative to those on placebo. There were no significant between group differences in recall accuracy observed at delayed testing. Recognition accuracy showed a slightly different pattern: while participants receiving levodopa demonstrated higher overall recognition accuracy during the learning block VS their placebo counterparts, they also demonstrated higher recognition accuracy VS placebo during delayed testing. No effect of object familiarity on recall or recognition was observed for either group. CONCLUSION: Interestingly, we noted an increase in accuracy from Day 4 to Week 1 across both recall and recognition for both drug arms, despite the lack of any training sessions in between. One potential explanation for this observation is the use of a combined learning approach (i.e. auditory presentations of novel words accompanying pictured objects), in comparison with previous work employing solely visual presentations for both words and objects. In further contrast to previous work, individual participants’ sensitivity to reward did not meaningfully predict novel word learning performance as indexed by our task. We propose that an explicit learning paradigm may produce a strong top-down motivational drive within the task context, which could in turn wash out contributions from reward sensitivity to learning outcomes.
Topic Areas: Language Development/Acquisition, Language Production