Child Development, xxxx 2016, Volume 00, Number 0, Pages 1–21 A New View of Language Development: The Acquisition of Lexical Tone Leher Singh and Charlene S. L. Fu National University of Singapore Research in first language development draws disproportionately from nontone languages. Such research is often presumed to reveal developmental universals in spite of the fact that most languages are tone lan- guages. Recent research in the acquisition of tone languages points to a distinct course of development as compared to nontone languages. Our purpose is to provide an integrated review of research on lexical tone acquisition. First, the linguistic properties and origins of tone languages are described. Following this, research on the acquisition of tones in perception and production is reviewed and integrated. Possible reasons for the uniqueness of tone in language acquisition are discussed. Finally, theoretical advances promised by further research on tone acquisition and specific research directions are proposed. Several decades of experimental research in lan- such, the majority of research on normative lan- guage acquisition have led to momentous discover- guage acquisition draws disproportionately from a ies about the young language learner. From these minority of languages. A natural consequence is findings, we can chart normative pathways to lan- that foundational theories of language development guage proficiency from infancy through the forma- may not necessarily generalize to the population. tive years and, as a consequence, advance basic Our objective is to provide a review and integra- theories of language development. To date, research tion of literature that investigates the acquisition of in the field of developmental psycholinguistics has lexical tone over the first 3 years of life. We begin focused primarily on children’s acquisition of by providing an introduction to lexical tone, defin- Romance and Germanic languages (e.g., English, ing properties of lexical tones and describing cues Spanish, and French), thus drawing from a limited relevant to the psycholinguistic processing of tone. range of language systems that use vowels and con- Following this, we review and integrate literature sonants to contrast word meanings (nontone lan- on the perception of tones within three central guages). However, most human languages are tone domains of first language acquisition: (a) the forma- languages and use lexical tone in addition to vow- tion of phonetic categories for tone, (b) the matura- els and consonants to draw meaningful distinctions tion and stabilization of tone categories, and (c) the between words by systematically manipulating integration of lexical tone into a child’s developing vocal pitch (Yip, 2002). For example, in Mandarin lexicon. We then progress to a review of the devel- Chinese, the mostly widely spoken tone language, opment of tone production abilities in early child- the word “ma” assumes different meanings based hood, focusing on constraints on early tone on the tone in which it is produced. “Ma” means production and on the pathway to mature tone pro- “mother” when spoken in Tone 55, “hemp” when ductions within the tone language learning child. spoken in Tone 35, “horse” when spoken in Tone Further to this, we discuss possible reasons why 214, and “to scold” when spoken in Tone 51. The tone may develop in ways that are unique in com- use of tone is widespread among languages of the parison to vowels and consonants. We then pro- world with an estimated 60%–70% of languages gress to situate our review of empirical research presumed to be tone languages (Yip, 2002). As within broader theories and models of normative language development. Finally, we propose future empirical directions for research in tone language We are grateful to the Ministry of Education Tier 1 Academic development that could potentially inform and Research Fund grant (FY2013-FRC2-009) and a start-up grant fi fi from the National University of Singapore to Leher Singh to sup- advance the eld of rst language acquisition. port the research reviewed in this manuscript. We thank Thi- langa D. Wewalaarachchi and Liang Hui Wong for valuable comments on this manuscript. Correspondence concerning this article should be addressed to © 2016 The Authors Leher Singh, Department of Psychology, National University of Child Development © 2016 Society for Research in Child Development, Inc. Singapore, 9 Arts Link, Singapore 117570. Electronic mail may be All rights reserved. 0009-3920/2016/xxxx-xxxx sent to [email protected]. DOI: 10.1111/cdev.12512 2 Singh and Fu ture, but primarily identified by F variation An Introduction to Lexical Tone 0 (Gandour, 1978). As such, the primary acoustic– Lexical tone refers to syllable-level shifts in the phonetic cues associated with tone production dif- fundamental frequency contour that draw distinc- fer from that associated with the production of con- tions between the meanings of words. Lexical tone sonants and vowels. is primarily identified by fundamental frequency The origin of tone in human languages (known (or pitch), drawing on specific cues such as mean as “tonogenesis”) has been extensively documented pitch and pitch contour (Chandrasekaran, Sampath, in South East Asian languages, such as Mandarin & Wong, 2010; Gandour, 1983, 1984; Whalen & Chinese and Vietnamese (see Haudricourt, 1954; Xu, 1992). However, lexical tone is not determined Matisoff, 1973; Thurgood, 2002). Tone is thought to by pitch movements alone. Rather, there are other have evolved due to the monosyllabic nature of secondary cues to tone identity, most commonly particular languages, which resulted in syllables reported to be duration, amplitude, vocal range, that contained a wide variety of consonant sounds and the register of a speaker (Blicher, Diehl, & that were used to contrast meaning. Gradually, Cohen, 1990; Edmondson & Esling, 2006; Leather, differences between certain consonants were 1983; Liu & Samuel, 2004; Whalen & Xu, 1992; neutralized. Tones then reportedly emerged as a Wong & Diehl, 2003). Secondary cues support way to maintain distinctiveness between similar- native listeners’ identification of tones when pitch sounding words (Matisoff, 1973). In particular, it is cues are removed or obscured (Liu & Samuel, proposed that in early phases of the evolution of 2004; Whalen & Xu, 1992). Therefore, although tones, pitch height of tones originated from the tone is most commonly defined by pitch changes attrition of syllable-initial consonant contrasts and in psycholinguistic research, in actual fact, a pitch contours from the attrition of syllable-final broader range of acoustic cues work in concert to consonants (Haudricourt, 1954). drive tone identification. However, the research Relevant to their linguistic origin, tone languages reviewed herein focuses predominantly on the per- are not randomly distributed throughout the world. ception and production of tones as defined by Rather, they aggregate within certain geographical pitch cues. regions where they serve as the linguistic norm. The expression of lexical tone is somewhat This patterning has led to conclusions that contact dependent on other phonetic segments, such as with neighboring languages has contributed to the vowels and consonants. Tone is typically instanti- emergence of particular tone languages (e.g., tone in ated on the vowel, but the realization of tone inter- Vietnamese is thought to have emerged from inten- acts with surrounding consonants (Hombert, Ohala, sive contact with Chinese languages; Matisoff, & Ewan, 1979; Lee, 2000). However, lexical tone is 2001). Regions with a high concentration of tone crucially different to vowels and consonants in two languages include sub-Saharan Africa and continen- primary ways. First, lexical tone entails syllable- tal and mainland South East Asia (Indochinese level changes, while vowels and consonants entail Peninsular), Central America, the Caribbean, and segmental changes. As a result, tone is sometimes the Amazon basin. Tone languages are rare in Eur- classified as a suprasegmental cue, whereas vowels ope, North Africa, and America. The geographical and consonants are incontrovertibly classified as aggregation of tones may be due to the fact that segmental cues. Second, there are differences in the tone languages may have spread via contact with acoustic composition of vowels, consonants, and other tone languages in the region. A second pro- tones, most notably in the distribution of acoustic posed reason (not mutually exclusive from the first) energy, which is clearly observable in spectral anal- is that there may be a significant concordance ysis. During speech production, the vocal tract per- between the population frequency of specific mits the concentrated passage of acoustic energy at genetic expressions and the areas in which tone lan- particular frequencies (while limiting the passage of guages are commonly spoken, suggesting that some sound at other frequencies). Formants refer to the populations may also have a genetic predisposition high concentrations of acoustic energy that are per- to tone. Two particular genes, ASPM-D and MCPH- mitted to pass through the vocal tract. Vowels and D, have been thought to affect neural organization consonants are related to formant properties (specif- in subtle ways that favor perception and acquisition ically, frequency values and transitions) and are not of linguistic tone (Dediu & Ladd, 2007). typically defined in terms of fundamental frequency Tone languages are not all alike