High tone lowering and raising in Tsua

The Tsua language is an Eastern Kalahari Khoe language of Botswana (Chebanne 2014). Tsua tone production displays complex Fundamental Frequency (F0) trajectories. Lexical data show that this language has three tone levels: High (H), Mid (M), and Low (L), with the following surface tone melodies: [HH, HM, HL, MM, MH, ML]. High tones may be lowered when they occur following voiced obstruents, aspirated obstruents or the glottal fricative /h/ in root-initial position, a typologically rare pattern. This results in two depressed melodies: depressed HM[DH-M] and depressed HL [DH-L]. Both clicks and non-clicks participate in this interaction. We refer to this tonal depression pattern as High Tone Lowering (HTL). HTL may be formally accounted for via the Low tone insertion rule: ∅ → L / [-sonorant, +slack] ___ H [-H] #. Recent analysis suggests that Super High (SH) tones are derived from /H/ when docked to the high vowels [i], [u] and are not phonemic. For example, underlying /HL/ tűù “to collect and remove ash” is produced with SH-L tones on the surface. We refer to this as High Tone Raising (HTR). Elderkin (1988) reports a similar finding in Ju|ʼhoan in which a sequence of successive extrahigh tones is only found in click-initial morphs when the final vowel is [i] or [u]. It may be that an Intrinsic F0 (IF0) effect from the Tsua high vowels was a historical factor that led to the genesis of HTR. Given that voiced, aspirated and /h/ consonant types depress a root-initial H tone and the high vowels [i], [u] raise H tones, the paper considers phonetically-driven origins of these patterns.Keywords: tone; depressor consonants; high vowels; Khoisan; Intrinsic F

An SS ANOVA (Smoothing Spline Analysis of Variance) study of high tone lowering in Tsua

This article examines the acoustic phonetic properties of consonant-tone interaction in the Khoisan language, Tsua, using speech production data from original field research in Botswana. The Tsua tonal melodies with Fundamental Frequency (F0) shapes having the most extreme excursions are the result of a rare consonant-tone interaction pattern with depressor types found in both African and East Asian tone languages. The Tsua depressor types are voiced obstruents, aspirated obstruents and the glottal fricative /h/. Statistical analysis via Smoothing Spline Analysis of Variance (SS ANOVA) reveals two striking generalisations: (i) only root-initial High tones followed by a non-High tone are depressed; and (ii) the overall shapes of the F0 curves are more important for tone melody identification than whether they are produced at a slightly higher or lower Hertz value, even if the difference is statistically significant. The first finding reflects the context-dependent nature of Tsua tonal depression. The second stands in contrast to studies of other tone systems that suggest the relative Hertz differential between adjacent tones is more important for identification. These findings expand our knowledge of tonal phonetics by showing what is possible in a typologically rare tone system, and highlight the importance of statistical methods in phonetic fieldwork