Final answer:
Vowels that occur around nasal consonants or are produced by individuals with VP insufficiency experience a decrease in formant intensity due to nasalization and the coupling of the nasal cavity with the vocal tract, leading to altered acoustic properties.
Step-by-step explanation:
When vowels are produced before or after nasal consonants, or by speakers with velopharyngeal (VP) insufficiency, there is a distinctive change in the acoustic properties of these vowels. Specifically, the intensity and the bandwidth of the vowel formants are affected. The presence of the nasal consonants introduces additional nasal formants and antiformants, which can cause the oral formants to decrease in intensity. Furthermore, due to the nasal cavity coupling with the vocal tract during the production of these nasalized vowels, there may be a dampening effect, reducing the sharpness and energy of the formants.
Velopharyngeal insufficiency leads to a situation where the velopharyngeal mechanism does not close completely, allowing air to escape through the nose and causing a hypernasal speech quality. This also results in the reduction of formant intensity as the acoustic energy is split between the oral and nasal tracts. Therefore, in both cases—vowels surrounding nasal consonants and those produced by speakers with VP insufficiency—formant intensity decreases, and the acoustic quality of the vowel sounds is altered.