H-and-H model

Lindblom's theory of Hyper and Hypo-articulation claims that speakers vary articulatory clarity according to the informational requirements of their listener: speakers hyper-articulate when listeners require maximum acoustic information, and reduce articulatory effort when listeners can supplement the acoustic input with information from other sources (Lindblom, 1990). To prevent speakers from over-economising to a point of unintelligibility, hypo-articulation is governed by a constraint of lexical distinctiveness: speakers hypo-articulate only while listeners are able to distinguish the target from competing lexical items.

Link
Utrecht Lexicon of Linguistics