The schematic below shows a cross section of a human vocal tract, with its articulators:
- Lips
- Tongue: tip/blade
- Tongue: body
- Tongue: root
- Velum (soft palate)
- Vocal folds
…and their points of articulation:
- Lips
- Teeth
- Alveolar ridge
- Hard palate
- Velum (soft palate)
- Uvula
- Pharynx (throat)
- Glottis (space between the vocal folds)
Inside this vocal tract is a simplified phonetic chart, showing symbols that represent various types of speech sounds, from most obstructed to least:
- Stops
- Fricatives
- Approximants
- Vowels
Tongue-body positions for front and back vowels correspond to palatal and velar places of consonant articulation respectively.
Degree of Stricture
Speech sounds can be organized on a continuum of most obstructed to least obstructed: from full obstruction (stops); through partial obstruction (fricatives); through loose, brief, and relative obstruction (approximants); to unobstructed vowel sounds. Changing the degree of obstruction of a familiar articulation can help us conceptually navigate the oral space and produce unfamiliar speech sounds.
As an example, progressively tightening the stricture on a close front vowel /i/ moves that tongue shape through palatal approximant territory /j/ into a fricative sound /ʝ/ and eventually to a stop /ɟ/. Another example: Progressively loosening the stricture from the stop /ɡ/ will lead to fricative /ɣ/ and then approximant /ɰ/. Adding lip rounding to this shape will produce approximant /w/ or, when lengthened, vowel /u/.
For more on this concept, please see: https://ktspeechwork.org/geography-of-speech/