Neural Processing of Tone Sandhi in Production and Perception: The Case of Mandarin Tone 3 Sandhi

Language-specific and context-dependent phonological rules of lexical tone are prevalent in tone languages. Such rules are commonly referred to as tone sandhi. One of the most studied sandhi rules is Mandarin Tone 3 sandhi. In Mandarin, Tone 3 followed by another Tone 3 is pronounced as Tone 2 (33 → 23). In this chapter, we reviewed our current understanding of the processing of Tone 3 sandhi. Two important and relatively well-investigated questions are whether Tone 3 sandhi involves on-line tone substitution in speech production and whether the auditory representations of Tone 2 and Tone 3 are less distinct from each other due to the acquisition of Tone 3 sandhi. Recent behavioral studies demonstrated that in the lexical decision task, only Tone 3 had a facilitation effect on targets carrying tone sequence 33, while in the picture-naming task, a facilitation effect was found with both Tone 2 and Tone 3. These results supported that Tone 3 sandhi involves on-line tone substitution, in line with fMRI studies showing that Tone 3 sandhi resulted in higher activation in the right pIFG, which is known to engage in articulatory representations and their sequencing. Regarding tone perception, previous behavioral studies showed that the acquisition of Tone 3 sandhi led to worse performance at discriminating Tone 2 and Tone 3. Further, the contrast between Tone 2 and Tone 3 is consistently reported to elicit reduced MMN compared to other tone pairs only in native speakers. One explanation of these findings is that the auditory representations of Tone 2 and Tone 3 activated each other due to Tone 3 sandhi. Namely, high-level phonological rule could modulate pre-attentive auditory processing. In the future, the role of linguistic context in the processing of tone sandhi needs more investigation, especially regarding how listeners retrieve the correct word/morpheme based on the contextual information.