The effect of overnight consolidation in the perceptual learning of non-native tonal contrasts

Abstract

Sleep-mediated overnight consolidation was found to facilitate perceptual learning by promoting learners generalization across talkers in their perception of novel segmental categories. Lexical tone differs from most segmental contrasts in that it is highly variable across talkers, and displays dynamic change over time. It remains unclear whether a similar (or a larger) effect of overnight consolidation would be found for perceptual learning of novel tonal contrasts. Thus, this study aims to examine whether overnight consolidation facilitates generalization across talkers in the discrimination and 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. Listeners were trained in a tone identification (ID) task using stimuli produced by a trained talker. Their development was then tested in the ID and AX discrimination tasks using stimuli produced by trained and untrained talkers in three posttests following training: immediately after training, 12-hour delay, and 24-hour delay. While the evening group slept between the first and second posttests, the morning group did not. The results of accuracy rates in the ID task showed that while Mandarin listeners trained in the evening showed an improved trend, predicted by their individual sleep time, in identifying the level tones produced by both the trained and untrained talkers, Mandarin listeners trained in the morning showed a declining trend. In contrast, the results of d-prime scores in the AX discrimination task did not show different developmental patterns between the two groups. Consistent with previous studies on segmental learning, the finding suggests that overnight consolidation might have assisted the evening trainees formation of a more abstract (talker-independent) representation of novel tone categories in memory traces. The results are discussed regarding the features of lexical tones to shed light on the mechanism of phonetic learning.