Consonant-tone interaction in the Khoisan language Tsua

• Published in: LingBuzz
• Main Author: Mathes, Timothy
• Format: Paper
• Language: English
• Published: Tromso Universitetet i Tromsoe 01.01.2015
• Subjects: Acoustic phonetics; Acoustics; Articulatory phonetics; Clicks; Consonants; Diachronic linguistics; Dissertations & theses; Fieldwork; Fricatives; Fundamental frequency; Khoisan languages; Language typology; Lexicon; Mental depression; Obstruents; Phonetics; Phonology; Smoothing; Sonorants; Sound change; Speech production; Tone; Variance analysis

This dissertation examines the acoustic phonetic properties of consonant-tone interaction in the critically-endangered and little studied Khoisan language Tsua, using speech production data from original field research in Botswana. Tsua exhibits an extreme tonal depressor effect that lowers a post-consonantal, root-initial High tone's production by 50 Hz or more when it is followed by a non-High tone and preceded by a voiced obstruent, aspirated obstruent or the glottal fricative /h/, a typologically rare pattern. However, this inquiry finds that 19.3% of the root-initial High tones that are expected to be lowered in the post-depressor context are not. It is argued that the tonal depression exceptions involving voiced obstruents correspond to historically nasal sonorants or nasalized clicks, consonants which are not depressors in Tsua synchronically or diachronically. Thus, voiced obstruents function as depressors in lexical items that have not undergone this historic sound change, an explanation referred to as the Tsua Depression Exceptions Hypothesis in this thesis. To tease apart the acoustic effects by depressor type, F0 curves are evaluated using Smoothing Spline Analysis of Variance (SS ANOVA), a domain-general statistical tool for the rigorous comparison of curves along multiple reference points (Gu 2002, 2013). Three main conditions in the implementation of depressed High tones are tested via SS ANOVA on normalized F0 z-scores: (i) when the depressed High tone follows voiced versus aspirated obstruents and is followed by a Mid tone; (ii) when the depressed High tone follows voiced versus aspirated obstruents and is followed by a Low tone; and (iii) when the depressed High tone is followed by a Mid versus Low tone regardless of depressor type. The effect on Mid tones preceded by depressors is examined as well. The results indicate that the F0 curve shapes are almost identical regardless of whether a root-initial High tone is produced following a root-initial aspirated obstruent or a root-initial voiced obstruent and when it precedes a Mid tone (i.e. DH-M). The F0 curve shapes are also quite similar when a root-initial depressed High tone is produced following aspirated obstruents as opposed to voiced obstruents and when it precedes a Low tone (DH-L). The F0 curve shapes from normalized time point 30 to the F0 peaks are similar when a depressed High tone precedes a Mid versus Low tone regardless of depressor type. There is no evidence to suggest that Mid tones undergo extreme depression in Tsua. Tsua tonal depression may be the result of a Low tone insertion rule given the nature of the F0 curves. The purported rule is not completely isomorphic as the Low tone insertion rule for depression in Ikalanga proposed by Hyman and Mathangwane (1998), as Tsua depression is more context dependent. Moreover, the Tsua depression pattern is not fully accounted for by the [L/voice] feature in Bradshaw's Multiplanar model of consonant-tone interaction. Formally, I account for the Tsua depression pattern via the Low tone insertion rule in (1). (1) Tsua tonal depression rule: Ø → L / [-sonorant, +slack] ___ H [-H] # The rule in (1) proposes that [+slack] is the key feature that unifies the depressor types pending further acoustic and articulatory supporting evidence. What is important is that a Low tone insertion account is plausible given modifications to previous proposals for other languages. It is unclear whether the rule in (1) is present in Tsua's phonology or if the current depression pattern is a remnant of Tsua's phonology from long ago. As a first step towards determining whether the rule is synchronically active, a two-part tone Wug Test is proposed for a future experiment. If the rule is found to be productive, this raises the interesting possibility that click replacement, a sound change process whereby a click consonant is replaced by another click or non-click consonant diachronically, may interact with rule application in some way, given the tonal depression exceptions for historically nasal clicks that were replaced by voiced clicks or voiced non-clicks. Such a possibility has not been explored in the Khoisan literature. The findings reported in this dissertation 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.