Quote:
Progressive metaphony, in which a vowel early in the word influences a subsequent vowel, can be distinguished from regressive metaphony, in which a vowel towards the end of the word influences a preceding vowel. (Progressive metaphony is sometimes called "left-to-right" metaphony, and regressive metaphony may be called "right-to-left" metaphony.)(link).
I think of umlaut more in the context of Germanic languages, though it happens sporadically in Romance, too. Cf. Genoese: ō can /u kaŋ/ 'the dog', i chen /i kɛŋ/ 'the dogs'. I have seen umlaut used in the literature though in reference to other languages, e.g., an Arabic dialect.

Ceci n'est pas un seing.