How sleep-mediated memory consolidation modulates the generalization across talkers: evidence from tone identification

Recent studies showed that sleep-mediated memory consolidation facilitated learners’ generalization across talkers in their perception of novel stop contrasts. Lexical tone is characterized by high variability across talkers. Thus a similar effect of overnight consolidation could be found for perceptual learning of novel tonal contrasts. This study aims to examine whether overnight consolidation facilitates talker generalization in the identification of novel Cantonese level tones by Mandarin listeners. Two groups of Mandarin listeners were perceptually trained either in the morning or in the evening using stimuli from one talker. Their post-training changes and generalization to a novel talker were then tested in three posttests over 24 hours using stimuli from the trained and untrained talkers. The results showed that the evening group showed an improved trend in identifying the level tones produced by both the trained and untrained talkers; in contrast, the morning group showed a declining trend. The finding of identification changes over time suggests that overnight consolidation might have assisted learning of tone stimuli produced by the novel talker, and eventually facilitated the formation of a more talker-independent representation of novel tone categories in long-term memory. The findings have implications for understanding the mechanism of speech learning and plasticity.