When articulating the Khasi open 'a' sound, what specific phonetic context causes it to become more closed, and how is this distinct from its typical pronunciation?

The typical Khasi open 'a' sound is a low central unrounded vowel, articulated with the tongue body positioned low and centrally in the oral cavity, often phonetically transcribed as [a]. This represents its most open pronunciation. The specific phonetic context that causes this Khasi open 'a' sound to become more closed is the influence of an adjacent palatal or palatalized consonant. A palatal consonant is produced by raising the tongue body towards the hard palate, the roof of the mouth behind the alveolar ridge. A palatalized consonant is one that acquires a secondary articulation with the tongue body raised towards the palate. When the open 'a' is next to such a consonant, either preceding or following it, the vowel undergoes assimilation. Assimilation is a phonological process where one sound becomes more similar to a neighboring sound. In this context, the high tongue position required for the palatal or palatalized consonant causes the tongue body to raise slightly during the articulation of the adjacent 'a'. This articulatory adjustment shifts the vowel from a maximally low tongue position to a mid-central or mid-front position, resulting in a less open quality. For example, in Khasi words like *kylla* (to change) or *tyngkai* (to save), where a consonant is palatalized before the 'a' vowel, the 'a' can be heard as more closed. This is distinct from its typical pronunciation because the typical 'a' involves the tongue being at its lowest possible position, maximizing the vertical opening of the oral cavity. When the vowel becomes more closed, the tongue body elevates, reducing the vertical space between the tongue and the roof of the mouth. This change moves the sound from a low, open vowel quality towards a mid-height vowel quality, perceptually altering it from a broad 'a' to a sound closer to a schwa [ə] (a mid-central unrounded vowel) or a mid-front unrounded vowel [ɛ] (like in "bed"), but generally less fronted than [ɛ]. The fundamental distinction lies in the change of tongue height: from maximally low for the typical 'a' to a perceptibly higher, mid-level position for the more closed variant.