It is commonly believed that second language (L2) acquisition of lexical tones presents a major challenge for learners from nontonal language backgrounds. This belief is somewhat at odds with research that consistently shows beginning learners making quick gains through focused tone training, as well as research showing advanced learners achieving near-native performance in tone identification tasks. However, other long-term difficulties related to L2 tone perception may persist, given the additional demands of word recognition and the effects of context. In the current study, we used behavioral and event-related potential (ERP) experiments to test whether perception of Mandarin tones is difficult for advanced L2 learners in isolated syllables, disyllabic words in isolation, and disyllabic words in sentences. Stimuli were more naturalistic and challenging than in previous research. While L2 learners excelled at tone identification in isolated syllables, they performed with very low accuracy in rejecting disyllabic tonal nonwords in isolation and in sentences. We also report ERP data from critical mismatching words in sentences; while L2 listeners showed no significant differences in responses in any condition, trends were not inconsistent with the overall pattern in behavioral results of less sensitivity to tone mismatches than to semantic or segmental mismatches. We interpret these results as evidence that Mandarin tones are in fact difficult for advanced L2 learners. However, the difficulty is not due primarily to an inability to perceive tones phonetically, but instead is driven by the need to process tones lexically, especially in multisyllable words.

Lexical tones are widely believed to be a formidable learning challenge for adult speakers of nontonal languages. While difficulties—as well as rapid improvements—are well documented for beginning second language (L2) learners, research with more advanced learners is needed to understand how tone perception difficulties impact word recognition once learners have a substantial vocabulary. The present study narrows in on difficulties suggested in previous work, which found a dissociation in advanced L2 learners between highly accurate tone identification and largely inaccurate lexical decision for tone words. We investigate a “best-case scenario” for advanced L2 tone word processing by testing performance in nearly ideal listening conditions—with words spoken clearly and in isolation. Under such conditions, do learners still have difficulty in lexical decision for tone words? If so, is it driven by the quality of lexical representations or by L2 processing routines? Advanced L2 and native Chinese listeners made lexical decisions while an electroencephalogram was recorded. Nonwords had a first syllable with either a vowel or tone that differed from that of a common disyllabic word. As a group, L2 learners performed less accurately when tones were manipulated than when vowels were manipulated. Subsequent analyses showed that this was the case even in the subset of items for which learners showed correct and confident tone identification in an offline written vocabulary test. Event-related potential results indicated N400 effects for both nonword conditions in L1, but only vowel N400 effects in L2, with tone responses intermediate between those of real words and vowel nonwords. These results are evidence of the persistent difficulty most L2 learners have in using tones for online word recognition, and indicate it is driven by a confluence of factors related to both L2 lexical representations and processing routines. We suggest that this tone nonword difficulty has real-world implications for learners: It may result in many toneless word representations in their mental lexicons, and is likely to affect the efficiency with which they can learn new tone words.

Mandarin Chinese tones are known to be difficult for second language learners. A large body of research has examined non-native perception of tones, and may provide useful and interesting insights about the sources of tone learning difficulty for Chinese teachers and learners. However, much of the literature is in journals that may be difficult to access or written in technical language that may be hard for non-specialists to understand. This review article aims to summarize key findings from this research in an accessible fashion. I will draw on the research to answer five broad questions: (1) Why are tones more difficult for some learners than others? (2) Why are some tones more difficult than others? (3) Why are tones in words more difficult than in meaningless syllables? (4) Why are tones in context more difficult than in isolation? (5) What can we do about tone learning difficulties?

People who grow up speaking a language without lexical tones typically find it difficult to master tonal languages after childhood. Accumulating research suggests that much of the challenge for these second language (L2) speakers has to do not with identification of the tones themselves, but with the bindings between tones and lexical units. The question that remains open is how much of these lexical binding problems are problems of encoding (incomplete knowledge of the tone-to-word relations) vs. retrieval (failure to access those relations in online processing). While recent work using lexical decision tasks suggests that both may play a role, one issue is that failure on a lexical decision task may reflect a lack of learner confidence about what is not a word, rather than non-native representation or processing of known words. Here we provide complementary evidence using a picture-phonology matching paradigm in Mandarin in which participants decide whether or not a spoken target matches a specific image, with concurrent event-related potential (ERP) recording to provide potential insight into differences in L1 and L2 tone processing strategies. As in the lexical decision case, we find that advanced L2 learners show a clear disadvantage in accurately identifying tone mismatched targets relative to vowel mismatched targets. We explore the contribution of incomplete/uncertain lexical knowledge to this performance disadvantage by examining individual data from an explicit tone knowledge post-test. Results suggest that explicit tone word knowledge and confidence explains some but not all of the errors in picture-phonology matching. Analysis of ERPs from correct trials shows some differences in the strength of L1 and L2 responses, but does not provide clear evidence toward differences in processing that could explain the L2 disadvantage for tones. In sum, these results converge with previous evidence from lexical decision tasks in showing that advanced L2 listeners continue to have difficulties with lexical tone recognition, and in suggesting that these difficulties reflect problems both in encoding lexical tone knowledge and in retrieving that knowledge in real time.