Final answer:
The nasal resonance encountered in high vowels is mostly attributed to the position of the tongue in the oral cavity, which directs more sound energy into the nasal cavity.
Step-by-step explanation:
High vowels have more nasal resonance than low vowels primarily due to the tongue position in the oral cavity. During the production of high vowels, the tongue is raised closer to the roof of the mouth, which reduces the volume of the oral cavity and directs more sound energy into the nasal cavity. This causes greater nasal resonance. The shape of the pharynx, frequency of the vowel, incidence of velopharyngeal insufficiency, and size of the oral cavity also play roles in the acoustic qualities of speech sounds, but the key factor contributing to the nasal resonance of high vowels is the tongue's position.