The human speech communication process

The nature of the human communication process through spoken language may best be illustrated in the following figure:

[click image to enlarge]

The Speech Chain cf. Denes & Pinson (1993: 5)

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 forward slash symbols, e.g., /a/, /p/, /b/ etc.

Sotho phonology research: a brief overview

Setswana is a member of the Sotho group of languages that share different phonetic and phonological features; the other languages are Sesotho sa Leboa (Sepedi) and Sesotho. 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, e.g., not going into detail of any specific theory applied by researchers at different points in time.

Notable contributions to the phonology of the Sotho languages have been made by Malepe (1966); Khoali (1985); Janson (1985); Kotzé (1987); Krüger (1987); Herbert (1990); Khabanyane (1991); Mmusi (1993); Dichabe (1997); Mosaka (2000); Coetzee (2001); Zsiga et al. (2006); Coetzee et al. (2007); Kotzé & Zerbian (2008); Coetzee & Pretorius (2010); Gouskova et al. (2011); Wissing (2012); Lubinda (2012); Nkolola-Wakumelo et al. (2012); Boyer & Zsiga (2013) and Bennett (2019).

Setswana 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”, i.e., Crystal (2008: 486). Three different tones are distinguished in Setswana, e.g., 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 researchers. 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 Sotho languages as indicated below:

Sotho tonology research: a brief overview

Research in this field include descriptive, theoretical, and experimental contributions with overlaps in some areas as provided by Dickens (1986); Kisseberth & Mmusi (1990); Creissels et al. (1997); Creissels (1998, 1999, 2000); Batibo & Mae (1999); Kisseberth (1998); Zerbian (2011); Wissing (2012) and Zerbian & Barnard (2008).

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.

As indicated in Figure 1 the speech chain in essence, comprises the following three phases: articulation phase (linguistic and physiological), transmission phase (acoustic) and perceptual phase (physiological and linguistic).

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 Setswana 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 Setswana may be found in grammar books such as Cole (1955) and monographs such as Doke (1954), and in dictionaries such as Matumo (1993) and articles such as Lombard (1982). 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 Krüger (1987: 43-48).

• 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 and perception. 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 listed below.

  Experimental studies in articulatory phonetics of Setswana, Sebirwa, Shekgalagari and Sesotho include:

  • X-ray techniques applied in the description of the vowels of Sesotho by Westphal (1971).
  • Cinefluorographic and X-ray techniques applied to the description of vowels segments of Sesotho by Roux (1979).
  • Electro-aerometer tools measuring relative flow of air from the nose and mouth in the articulation of, for instance, labialised ejectives and aspirated consonants in Sesotho by Roux (1979).
  • Ultrasonic techniques in the study of consonant systems of Setswana and Sebirwa by Zsiga (2005).
  • An electro-laryngograph study of plosives in Shekgalagari by Monaka (2005).
  • Ultrasonic techniques in the production of labiocoronal fricatives in Setswana by Havenhill et al. (2017).
  • Laryngographic and acoustic study on post-nasal devoicing in Shekgalagari by Solé et al. (2010).

Transmission phase

The articulation of a sound or sequence of sounds create sound waves that are transmitted through the air. This transmission phase is the domain of acoustic phonetics. The spectrograph is an instrument used in acoustic studies producing spectrograms which are visual representations of the spectra of frequencies of speech signals. Applicable computer software for analyzing, synthesizing, and manipulating speech are commonly used as tools for research in this domain. A program entitled PRAAT with excellent functions is widely used for research in this field (Boersma & Weenink, 2001).

Notable studies related to the acoustics of Sotho languages include the works of Khabanyane (1991); Dufberg (1986-1987); Roux (1979, 1980, 1984, 2003); Selebeleng (1997); Wissing & Roux (1995); Barnard & Wissing (2008); Wissing (2005, 2010a, 2010); Wissing et al. (1998); Zsiga (2005); Le Roux & Le Roux (2008); Le Roux (2012); Boyer & Zsiga (2013); Havenhill et al. (2017); Solé et al. (2010); Gouskova et al. (2011); and Duran et al. (2017).

Perceptual phase

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

• Perceptual studies related to the Sotho languages: Roux (1984, 2003); Zsiga (2005) and Wissing & Roux (2017).

Annotated digital speech data for Setswana and other Sotho languages are freely available for research and educational purposes at the South African Centre for Digital Language Resources (SADiLaR).

Setswana

• NCHLT Setswana Speech Corpus

  Orthographically transcribed broadband speech corpus of approximately 56 hours, including a test suite of 8 speakers.

• NCHLT Setswana Auxiliary Speech Corpus

  The corpus contains orthographically transcribed broadband speech in each of South Africa's eleven official languages. Transcriptions are provided in XML format.

Sesotho

• NCHLT Sesotho Corpus

  Orthographically transcribed broadband speech corpus of approximately 56 hours, including a test suite of 8 speakers.

• NCHLT Sesotho Auxiliary Speech Corpus

  The corpus contains orthographically transcribed broadband speech.

• Sesotho vowel speech data set

  The primary aim of this speech dataset was to collect a representative set of words in which all the Sesotho vowels are present.

• African Speech Technology Sesotho Speech Corpus

  African Speech Technology speech and transcription data for the Sesotho database. The “speech” directory contains Sesotho speech as spoken by Sesotho mother tongue speakers.

• Lwazi II Sesotho TTS Corpus

  Orthographic and phonemically aligned transcriptions.

• Lwazi Sesotho ASR Corpus

  Complete audio recordings and orthographic transcriptions used for Lwazi speech recognition systems.

• Sesotho tone data set

  These recordings are of male and female speakers of the QwaQwa region (Eastern Free State).

Sesotho sa Leboa / Sepedi

• NCHLT Sepedi Speech Corpus

  Orthographically transcribed broadband speech corpus of approximately 56 hours, including a test suite of 8 speakers.

• NCHLT Sepedi Auxiliary Speech Corpus

  The corpus contains orthographically transcribed broadband speech in each of South Africa's eleven official languages.

• Lwazi Sepedi TTS Corpus

  Orthographic and phonemically aligned transcriptions

• Lwazi Sepedi ASR Corpus

  Complete audio recordings and orthographic transcriptions used for Lwazi speech recognition systems.

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