The role of prior knowledge in second-language learners’ overnight consolidation of Cantonese tones

• Prior knowledge facilitated Cantonese tone learning through overnight consolidation. • Contour-tone contrasts consistent with prior knowledge were preferentially consolidated. • The preferential effect was positively predicted by Mandarin listeners’ deep-sleep length. • Different consolidation patterns were found between Mandarin and English listeners. This study examines the role of prior (tonal) knowledge in memory consolidation of non-native tones after an overnight sleep. While memory consolidation is beneficial in learning new sounds in a second language, only new linguistic information consistent with the existing knowledge is often prioritized for consolidation. What remains unclear from the research is whether prior tonal knowledge from a native language (i.e., pitch contour signaling the Mandarin contour-tone system) influences an overnight consolidation of tone learning. The study adopts an overnight design, using Cantonese contour and level tones contrasting in pitch contour and height, for two perceptual learning experiments conducted separately on Mandarin and English-speaking novice learners of Cantonese. The first experiment found that Mandarin-speaking participants showed a stronger effect of consolidation in novel words contrasting in contour tones than in level tones, thanks to their prior knowledge of contour tones. The consolidation effect was predicted by rough estimates of deep-sleep length. Without prior knowledge of tones, English-speaking L2 learners in the second experiment showed an (unexpected) offline improvement for both contour and level tones. Overall, the findings suggest a preferential effect on overnight consolidation of contour tones when the cues contrasting L2-Cantonese tones are consistent with L1-Mandarin prior knowledge.