The human speech communication process

The nature of the human communication process through spoken language may best be illustrated in the following figure. Figure 1 below as presented by Denes & Pinson (1993) provides a good point of departure:

[click image to enlarge]

The initial and final (linguistic) levels above mainly relate to mental activities, whilst the physiological and acoustic levels represent physical aspects of the communication process. These two aspects can be examined as underlying (phonemic) elements being transformed to surface (phonetic) representations. The study of these events take place in the respective domains of phonology and phonetics.

Phonology is “(A) branch of linguistics which studies the sound systems of languages. Out of a very wide range of sounds vocal apparatus can produce, and which is studied by phonetics, only a relatively small number are used distinctively in any one language.” Crystal (2008: 365). These sounds with distinctive values are labelled as phonemes which are represented between slash symbols, e.g. /a/, /p/, /b/ etc.

A brief overview of Nguni phonology research

IsiXhosa is a member of the Nguni group of languages that share different phonetic and phonological features; the other languages are isiZulu, Siswati and isiNdebele. Various theories have been developed to describe and explain the functioning of these phonemes. The discussions on phonological processes that will follow will however be theory neutral, i.e., not going into detail of any specific theory applied by researchers at different points in time.

Notable contributions to the phonology of Nguni languages have been made by Lanham (1960, 1970); Herbert (1977); Khumalo (1987); Msimang (1989); Jokweni (1995); Sibanda (2009); Zerbian (2003, 2004); Ndlovu (2010) and Podile (2020).

IsiXhosa is a tone language which is a language in which pitch differences function to differentiate words while tonology is “(T)he study of the forms and uses of tone in language.” Crystal (2008: 486). Three different tones are distinguished in isiXhosa, i.e., a high tone, a low tone and a high falling tone. However, no tone markings are displayed in the orthography of the language. In some specific cases however, tone may be indicated in the event of ambiguity and may respectively be indicated with the following symbols: high with the acute sign / ´ /, low with the grave sign / ՝ /, and high-falling with the circumflex sign / ^ /. Some dictionaries may include tonal markings.

Descriptions of the tonal features of these languages are mainly based on impressionistic observations of the researcher. The use of tones comes quite naturally from the speakers of the language. Non mother tongue speakers however may not always be so sure about what they perceive and thus, many tonal descriptions are inconsistent. This is manifested in dictionaries that do provide tonal markings as well as in descriptions of researchers. Roux (2003) provides some examples of inconsistencies in the perception and description of tone in the Sotho and Nguni languages. Nevertheless, several descriptions have been produced describing tonal patterns in the Nguni languages as listed below.

A brief overview of Nguni tonology research

Research in this field include descriptive, theoretical, and experimental contributions with overlaps in some areas. Contributions of descriptive nature are found in the works of Cope (1959, 1966, 1970); Lanham (1958); Rycroft (1963, 1980a, 1980b); Westphal et al. (1967); Louw (1968); Khumalo (1981a, 1981b, 1982); Creissels (1996); Davey (1981); Traill et al. (1987) and Claughton (1992).

Research conducted with reference to specific theoretical models are reflected in Cassimjee (1998); Cassimjee & Kisseberth (1992); Jokweni (1995, 1998); Downing (1990, 2001); Downing & Rialland (2017); Laughren (1984); Ham (1997); Silverman (2000); Clark (1988); Goldsmith et al. (1989) and Khumalo (1987).

The seminal work of Zerbian & Barnard (2008) provides an excellent experimental overview of the phonetics of intonation of South African Bantu languages and the implications for speech technology developments in these languages, Govender (2006) and Govender et al. (2007).

Phonetics is “(T)he science which studies the characteristics of human sound-making, especially those sounds used in speech, and provides methods for their description, classification and transcription.” Crystal (2008: 363).

Speech sounds or phones are indicated in brackets, e.g., [a], [p], [k] etc.

Phonetics manifests itself in the following three phases:

Articulation phase

This process where a sound or a series of sounds are formed, may be referred to as the articulation process. Articulatory phonetics is the study of these events which take place in two different modes:

• Impressionistic mode: in this mode, linguists/phoneticians make use of their knowledge of the nature and specific functions of the vocal organs of speech production. They identify, through introspection, the different manners on how sounds are formed. For instance, closure of both lips may produce stop sounds such as [b], [p], [m] which are labelled bi-labial sounds; pressing the tip of the tongue against the back of the alveolar ridge will produce alveolar sounds such as [t], [d], [n]; lowering the tongue in the oral cavity, opening the mouth and pushing air from the lungs with a vibration of the vocal folds will produce a low vowel such as [a].

  Many descriptions of the sounds of a language such isiXhosa are impressionistically based. These descriptions are often found as introductory chapters in a variety of grammar books on the specific language. These descriptions have often been regarded as appropriate for students learning a language, or for researchers interested in phonological processes taking place in a particular language. Examples of these types of descriptions for isiXhosa may be found in grammar books such as Oosthuysen (2016) and Doke (1954). In some of these cases diagrammatic sketches of the organs of speech corresponding to the alleged articulation of sounds are presented as visual demonstrations, as in for instance in Finlayson et al. (1991) for isiXhosa and Taljaard & Snyman (1989) for isiZulu.

• Instrumental mode: studying the nature and functions of the organs of speech, researchers in for instance, the fields of anatomy, physiology, speech pathology etc. need to have a more objective manner of describing the production of speech than relying on subjective impressionistic judgements. Therefore, different types of techniques and instruments are used to investigate the nature of speech production. Results of these types of research have found their way into the domain of phonetics and phonology presenting verifiable information regarding the speech communication process and providing explanations for phonological processes. This approach is referred to as Experimental or Instrumental phonetics which is conducted in all three phases of the communication process, i.e., for articulation, transmission (acoustics) and perception as will be listed below.

• An electro-palatographic study of click articulations in isiZulu and isiXhosa was made at the School of Oriental and African Studies in 1995. Examples are presented in inventory of click sounds.
• Scharf et al. (2007) experimental phonetic considerations on the phonetic representation of clicks.
• An articulatory description of clicks by means of electromagnetic articulography by Scharf et al. (1995).

Transmission phase

The articulation of a sound or sequence of sounds create sound waves that are formed transmitted through the air. This transmission phase is the domain of acoustic phonetics.

Typical instruments used in this domain are:

• The spectrograph which is an instrument producing spectrograms. A spectrogram is a visual representation of the spectrum of frequencies of a speech signal, also referred to as a voiceprint or sonograph.
• Software for speech research: PRAAT is a computer program for analysing, synthesising, and manipulating speech. It has been developed since 1992 by Boersma & Weenink at the Institute of Phonetic Sciences of the University of Amsterdam (Boersma & Weenink, 2001).

A selection of studies related to the acoustics of Nguni languages may be noted:

• isiXhosa:
  • Jessen & Roux (2002); Jessen (2002); Jones & Roux (2004); Dogil et al. (1996a, 1996b, 1996c); Roux (1991, 2007); Roux & Holtzhausen (1989); Roux et al. (1995); Jones et al. (1998b); Roux & Dogil (1997); Kilian (2017); Sands (1990, 1991) and Naidoo (2012).
• isiZulu:
  • Naidoo (2007, 2010).
• siSwati:
  • Kockaert & Godwin (1997) and Kockaert (1997).

Perception phase

Speech perception refers to the process by which human speech sounds are heard, interpreted and understood.

The following selected experimental studies related to speech perception in Nguni languages are: Jones et al. (1998a); Jones (2000); Lewis (1998); Roux (1983, 1995, 2003); Roux & Holtzhausen (1989) and Roux & Lewis (1999).

Annotated digital speech data for isiXhosa are available for research and educational purposes at the South African Centre for Digital Language Resources (SADiLaR).

• African Speech Technology isiXhosa Speech Corpus: African Speech Technology speech and transcription data for the isiXhosa database. The “speech” directory contains isiXhosa speech as spoken by isiXhosa mother tongue speakers.
• NCHLT isiXhosa Speech Corpus: Orthographically transcribed broadband speech corpus of approximately 56 hours, including a test suite of 8 speakers.
• Lwazi III isiXhosa TTS Corpus: Complete audio recordings with orthographic transcriptions. TTS corpus for standard SA dialect. This corpus was created to enable the building of a TTS voice.
• Lwazi isiXhosa ASR corpus: Complete audio recordings and orthographic transcriptions used for Lwazi speech recognition systems.

Boersma, P. & Weenink, D. (2001) ‘PRAAT, a system for doing phonetics by computer’. Glot international. 5: 341-345.

Cassimjee, F. & Kisseberth, C. W. (1992) ‘The tonology of depressor consonants: Evidence from Mijikenda and Nguni’. Annual Meeting of the Berkeley Linguistics Society. 18(2): 26-40.

Cassimjee, F. (1998) Isixhosa Tonology: An Optimal Domains Theory Analysis. München: Lincom.

Clark, M. M. (1988) ‘An accentual analysis of the Zulu noun’. In Van der Hulst H. & Smith N. (eds.). Autosegmental studies on pitch accent. Dordrecht: Foris Publications pp 51–79.

Claughton, J. (1992) The tonology of Xhosa. Doctoral Thesis. Rhodes University, Makhanda (Grahamstown).

Cope, A. T. (1959) ‘Zulu Tonology’. Afrika und Übersee. 43(3): 190-200.

Cope, A. T. (1966) Zulu phonology, tonology and tonal grammar. Doctoral Thesis. University of Kwa-Zulu Natal (University of Natal), Durban.

Cope, A. T. (1970) ‘Zulu Tonal Morphology’. Journal of African Languages. 9(3): 11-152.

Creissels, D. (1996)‘A domains-based approach to Swati tone’. MS Round Table on Bantu Historical Linguistics (MRASH). Lyon.

Crystal, D. (2008) A Dictionary of Linguistics and Phonetics. Oxford: Blackwell Publishers.

Davey, A. (1981) Aspects of the tonology of SiSwati. Doctoral Thesis, University of South Africa, Pretoria.

Denes, P. B. & Pinson, E. N. (1993) The Speech Chain: The Physics and Biology of Spoken Language, 2nd edn. Oxford: W. H. Freeman.

Dogil, G. & Roux, J. C. (1996a) ‘Notes on unencoded speech: Clicks and their accompaniments in Xhosa’. Proceedings of the Sixth Australian Conference on Speech Science and Technology. Australian Speech Science and Technology Association, Canberra. (pp. 55-60).

Dogil, G., Mayer, J. & Roux, J. C. (1996b) ‘Syllables and unencoded speech: Clicks and their accompaniments in Xhosa. Phonologica 1996. pp. 49-60.

Dogil, G., Roux, J. C., Mayer, J., Mavimbela, P. & Tuomi, S. (1996c) Speech coding and apraxic speech. Proceedings of the International Conference of Clinical Linguistics, München.

Doke, C. M. (1954). London: Oxford University Press. The Southern Bantu Languages

Downing, L. J. & Rialland, A. (eds.). (2017) ‘Intonation in African Tone Languages’. Phonology and Phonetics. 24. https://doi.org/10.1515/9783110503524.

Downing, L. J. (1990) ‘Local and metrical tone shift in Nguni’. Studies in African Linguistics. 21: 261-317.

Downing, L. J. (2001) ‘How ambiguity of analysis motivates stem tone change in Durban Zulu’. UBC Working Papers in Linguistics. 4: 39-55.

Finlayson, R., Jones, J., Phodile, K. & Snyman, J. W. (1991) An introduction to Xhosa phonetics. Hout Bay (Cape Town): Marius Lubbe Publishers.

Goldsmith J, Peterson, K. & Drogo, J. (1989) ‘Tone and accent in the Xhosa verbal system’. In Newman, P. & Botne, R. (eds.). Current approaches to African linguistics. Dordrecht: Foris. pp 157–178.

Govender, N. (2006) Intonation modelling for the Nguni languages. Master Dissertation. University of Pretoria, Pretoria.

Govender, N., Barnard, E. & Davel, M. (2007) ‘Pitch modelling for the Nguni languages’. South African Computer Journal. 38(1): 28–39.

Ham, W. H. (1997) ‘IsiXhosa verbal tonology: A comprehensive constraint-based account’. Working Papers of the Cornell Phonetics Laboratory. 11: 157-242.

Herbert, R. K. (1977) ‘Morphophonological palatalization in Southern Bantu: A reply to segmental fusion’. Studies in African Linguistics. 8: 143–171

Roux, J.C. (1991) ‘On ingressive glottalic and velaric articulations in Xhosa’. Proceedings of the 12th International Congress of Phonetic Sciences. Aix-en-Provence. pp. 158-161.

Jessen M. & Roux, J. C. (2002) ‘Voice quality differences associated with stops and clicks in Xhosa’. Journal of Phonetics. 30: 1-52.

Jessen, M. (2002) ‘An Acoustic Study of Contrasting Plosives and Click Accompaniments in Xhosa’. Phonetica. 59: 150-179.

Jokweni, M. W. (1995) Aspects of Isixhosa Phrasal Phonology. Doctoral Thesis, Urbana-Champaign University of Illinois, Champaign (Illinois).

Jokweni, M. W. (1998) ‘Parametric phonology and boundary tonology in Xhosa’. South African Journal of African Languages. 18(2): 29–32.

Jones, J. (2000) Xhosa intonational structures: An acoustic-perceptual investigation. Doctoral Thesis. Stellenbosch University, Stellenbosch.

Jones, J. J. & Roux, J. C. (2004) ‘An acoustic and perceptual analysis of queclaratives in Xhosa’. South African Journal for African Languages. 23(4): 223-236.

Jones, J., Louw, J. & Roux, J. C. (1998a). ‘Perceptual experiments on queclaratives in Xhosa’. South African Journal of Linguistics.36: 19-32.

Jones, J., Louw, J. & Roux, J.C. (1998b) ‘Queclaratives in Xbosa: an acoustic analysis’. South African Journal of Linguistics. 16(36): 3-18.

Khumalo, J. S. M. (1981a) Zulu tonology. Masters Dissertation, University of the Witwatersrand, Johannesburg.

Khumalo, J. S. M. (1981b) ‘Zulu tonology, Part 1’. African Studies. 40: 53-130.

Khumalo, J. S. M. (1982) ‘Zulu tonology, Part 2’. African Studies. 41: 3-125.

Khumalo, J. S. M. (1987) An autosegmental account of Zulu phonology. Doctoral Thesis. University of the Witwatersrand, Johannesburg.

Kilian, K. (2017) Vowel harmony in isiXhosa: an OT and acoustic study of [ATR]. Masters Dissertation. Rhodes University, Makhanda (Grahamstown).

Kockaert, H. J. & Godwin, D. (1997) ‘Voicing status of syllable-initial plosives in siSwati’. South African Journal of African Languages. 3: 100-104.

Kockaert, H. J. (1997) ‘Vowel harmony in siSwati: An experimental study of raised and non-raised vowels’. South African Journal of African Languages. 18: 2

Lanham, L. W. (1958) ‘The tonemes of Xhosa’. African Studies. 17(2): 65-81.

Lanham, L. W. (1960) The comparative phonology of Nguni. Doctoral Thesis. University of the Witwatersrand, Johannesburg.

Lanham, L. W. (1970) ‘Generative phonology and the analysis of Nguni consonants’. Lingua. 24: 155-162.

Laughren, M. (1984) ‘Tone in Zulu Nouns’. In Clements, G. N. & Goldsmith, J. (eds.). Autosegmental Studies in Bantu Tone. Dordrecht: Foris. pp. 183-234.

Lewis, P. W. (1998) Phonetic and phonological interference in Xhosa speech communication. Doctoral Thesis. Stellenbosch University, Stellenbosch.

Louw, J. A. (1968) The intonation of the sentence and its constituent parts in Xhosa and Tsonga. Pretoria: University of South Africa.

Msimang, C. T. (1989) Some phonological aspects of the Tekela Nguni languages. Doctoral Thesis. University of South Africa, Pretoria.

Naidoo, S. (2007) ‘A qualitative and quantitative study of Zulu affricates’. South African Journal for African Languages. 3: 83-96.

Naidoo, S. (2010) ‘A re-evaluation of the Zulu implosive [ɓ]’. South African Journal of African Languages. 30(1): 1-10.

Naidoo, S. (2012). ‘A comparative study of the explosive [b] and implosive [ɓ] in Nguni.’ In Ndinga-Koumba-Binza, H. S. & Bosch, S. (eds.). Language Science and Language Technology in Africa. Stellenbosch: SUN Press. pp. 21-32.

Ndlovu, S. (2010) Comparative reconstruction of Proto-Nguni Phonology. Riga: VDM Verlag.

Oosthuysen, J. C. (2016) The Grammar of isiXhosa. Stellenbosch: SUN MeDIA.

Podile, K. (2002) The dependency relations within Xhosa phonological processes. Masters Dissertation. University of South Africa, Pretoria.

Roux, J. C. & Holtzhausen, A. J. (1989) ‘An acoustic and perceptual analysis of Xhosa vowels’. South African Journal of African Languages. 9: 30-34.

Roux, J. C. & Lewis, P. J. (1999) ‘On Xhosa L2 speech and intelligibility’. Proceedings of the 14th International Congress of Phonetic Sciences. University of California, San Francisco. pp. 1149-1152.

Roux, J. C. (1983) ‘On the perception of vowel tone and vowel quality’. Handbook of the 10th World Congress of Phoneticians 45. Kobe, August

Roux, J. C. (1995) ‘On the perception and production of tone in Xhosa”. South African Journal of African Languages. 15(4):196-204.

Roux, J. C. (2003) ‘On the perception and production of tone in the Sotho and Nguni languages. Zulu’. Proceedings of the Third International Symposium on Cross linguistic studies of Tonal Phenomena. Tokyo University of Foreign Studies, Tokyo. pp. 155-176

Roux, J. C. (2007) ‘Unresolved issues in the representation and phonetic description of click articulations in Xhosa and Zulu’. Language Matters. 38(1): 8 -25.

Roux, J. C., Dogil, D. & Wokurek, G. (1995) ‘Click articulations in Xhosa: New perspectives through Wigner Distribution Analysis’. Proceedings of the XIIIth ICPhS. Stockholm. 2: 574-577.

Roux, J.C. & Dogil, G. (1997) ‘On the phonetic representation of clicks: Some experimental phonetic considerations’. 16th International Congress of Linguists. (July). pp. 20-25.

Rycroft, D. K. (1963) ‘Tone in Zulu Nouns’. African Language Studies. 4: 43-68.

Rycroft, D. K. (1980a). ‘Nguni tonal Typology and Common Bantu’. African Language Studies. 17: 33-76.

Rycroft, D. K. (1980b) ‘The Depression Feature in Nguni Languages and its Interaction with Tone’. Communication, 8. Department of African Languages. Makhanda (Grahamstown): Rhodes University.

Sands, B. (1990) ‘Some acoustic characteristics of Xhosa clicks’. UCLA Working Papers in Phonetics. 74: 96-103.

Sands, B. (1991) ‘Evidence for click features: Acoustic characteristics of Xhosa clicks’. UCLA Working Papers in Linguistics. 74: 6-37.

Scharf, G., Hertrich, I., Roux, J. C. & Dogil, G. (1995) ‘An articulatory description of clicks by means of electromagnetic articulography’. Proceedings of ICPhS XIII. 1: 50-53.

Sibanda, G. (2009) ‘Vowel Processes in Nguni: Resolving the Problem of Unacceptable VV Sequences’. Selected Proceedings of the 38th Annual Conference on African Linguistics, (Cascadilla proceedings project). Somerville, Massachusetts. pp. 38-55

Silverman, D. (2000) ‘Hypotheses concerning the phonetic and functional origins of tone displacement in Zulu’. Studies in African Linguistics. 29(2): 1-32.

Taljaard, P. C. & Snyman, J. W. (1989) ‘An introduction to Zulu phonetics’. Hout Bay (Cape Town): Marius Lubbe Publishers.

Traill, A., Khumalo, J. S. M. & Fridjhon, P. (1987) ‘Depressing facts about Zulu’. African Studies 46(2): 255–274.

Westphal, E. O. J., Notshweleka, M. & Tindleni, S. M. (1967) ‘Tonal Profiles of Xhosa Nominals and Verbo-nominals’. Communications in African Studies, 32. Cape Town: University of Cape Town.

Zerbian, S. & Barnard, E. (2008) ‘Phonetics of intonation in South African Bantu languages’. Southern African Linguistics and Applied Language Studies. 26(4): 235-254.

Zerbian, S. (2003) “Morphological Marking of Phonological Phrase Boundaries in Xhosa”. Proceedings of Prosodic Interfaces. pp. 209-214.

Zerbian, S. (2004) ‘Phonological Phrases in Xhosa’. ZAS Papers in linguistics. 37: 71 –99.