Mandarin-speaking Older Adults’ Memory Consolidation of Non-native Tonal Contrasts: The Role of Encoding Strength

Abstract

Newly learned words are initially encoded as episodic memories during training and later consolidated into long-term memory during post-training sleep, stabilizing these episodic memories or forming an abstract representation. 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 study aims 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 first investigated whether prior knowledge supports memory consolidation in Cantonese tone learning by recruiting 60 Mandarin-speaking older adults (≥ 55 years old), building upon the paradigm examined in prior research with younger adults. The participants were divided into two groups to examine the effects of overnight sleep versus wakefulness: the evening group, who were trained and took an immediate posttest in the evening, followed by two 12-hour delayed posttests (one with a trained talker and one with an untrained talker) after overnight sleep; the morning group, who were trained and took an immediate posttest in the morning, followed by the same delayed posttests after 12 hours of wakefulness. The results showed that, compared to younger adults, older adults did not exhibit the same memory enhancement with the trained talker, even with prior knowledge and overnight sleep. Only older adult high performers in the evening group displayed young adult-like consolidation patterns, which suggested that strengthening initial encoding might contribute to better overnight consolidation for the trained talker. However, overnight sleep promoted cross-talker perception of the contour-level tonal contrast.

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 adequate 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 tone learning for older adults through memory consolidation.

Date of Award	2025
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Zhen QIN (Supervisor)