Mechanisms of Word-Learning in Typical and Atypical Development

Abstract

The hippocampus plays a critical role in binding together information into an integrated memory, and memory for these arbitrary associations is important when learning new words. Recent studies have investigated a learning mechanism called fast mapping (FM), showing that rapid acquisition of novel arbitrary associations can be learned independent of the hippocampus. In the current study we examine word-learning across two conditions more and less likely to require information integration via the hippocampus in typically developing children and individuals with hippocampal dysfunction (e.g., Down syndrome). Individuals with Down syndrome (DS) manifest hippocampal dysfunction and display memory and learning difficulties, hence could potentially benefit from alternative learning strategies. The current study found no benefit of the FM condition in either group. Both groups performed similarly and above chance level across the two conditions and over a week's delay, but a delay by group interaction suggested that the typically developing children showed improvement across all conditions after 1 week whereas performance in DS stayed consistent. Given evidence for sleep deficits in DS we examined how sleep disturbance related to delayed word retention. Sleep efficiency did not appear to be driving maintenance in either group. Future studies investigating when an individual with DS sleeps after learning, could provide a better understanding of how sleep can influence the word learning process. Additionally, future studies in an older group of children can also provide information on when the hippocampus and sleep dependent learning may develop in childhood.