Abstract:

Newly learned words are initially encoded as episodic memories during training and later consolidated into long-term memory during post-training sleep. Prior knowledge, as a method for manipulating encoding strength, can accelerate consolidation. A recent study showed that Mandarin-speaking younger adults consolidated newly learned words contrasted by the Cantonese contour-level tonal contrast (but not the level-level contrast), due to their prior knowledge of Mandarin contour tones. However, older adults may experience different outcomes because of age-related changes in tone encoding and sleep architecture. Given these findings, this thesis aimed to explore the conditions supporting memory consolidation in aging and develop an optimized tone learning paradigm tailored to older adults’ needs.

This study involved two experiments. Experiment 1 explored whether prior knowledge facilitates memory consolidation in Cantonese tone learning by recruiting 60 eligible Mandarin-speaking older adults and replicating a paradigm previously used with younger adults. Participants were assigned to either an evening group (training and immediate posttest in the evening, followed by two 12-hour delayed posttests for the trained and untrained talker after sleep) or a morning group (training and immediate posttest in the morning, followed by the same delayed posttests after wakefulness). Results indicated that, unlike younger adults, older adults showed no memory enhancement for the trained talker despite prior knowledge and sleep, except for high-performing evening group participants who exhibited younger adult-like consolidation patterns, suggesting that stronger initial encoding may improve overnight consolidation. Notably, sleep enhanced cross-talker perception of contour-level tonal contrasts.

To further explore whether encoding strength could explain the lack of enhancement in older adults’ performance with the trained talker in Experiment 1, Experiment 2 increased the training length from six to 10 blocks in a new cohort of 60 participants, based on prior evidence suggesting that additional training can enhance encoding strength. The results demonstrated that training-enhanced encoding strength supported overnight improvement in contour-level tonal contrast for the evening group. This pattern, consistent with observations in younger adults, emerged when optimal pre-sleep encoding strength was achieved through prior knowledge and additional training.

This study highlights the crucial role of encoding strength in memory consolidation among older adults during tone learning. Theoretically, it sheds light on the mechanisms of memory consolidation in aging. Pedagogically, it tailors an optimized training paradigm to promote learning success for older adults through memory consolidation.