Phonetic naturalness and unnaturalness in Japanese loanword phonology

This paper argues that phonetic naturalness and unnaturalness can interact within a single grammatical system. In Japanese loanword phonology, only voiced geminates, but not voiced singletons, devoice to dissimilate from another voiced obstruent. The neutralizability difference follows from a ranking which Japanese speakers created on perceptual grounds: Ident(voi)_Sing » Ident(voi)_Gem. On the other hand, the trigger of devoicing-OCP(voi)-has no phonetic underpinning because voicing does not have phonetic characteristics that would naturally lead to confusion-based dissimilation (Ohala, Proceedings of Chicago Linguistic Society: Papers from the parasession on language and behaviour, 1981, in: Jones (ed.) Historical linguistics: Problems and perspectives, 1993). OCP(voi) in Modern Japanese originated as a phonetically natural OCP(prenasal) in Old Japanese because the spread out heavy nasalization would lead to perceptual confusion, but it divorced from its phonetic origin when prenasalization became voicing. The interaction of the three constraints in Modern Japanese suggests that phonetic naturalness (the ranking Ident(voi)_Sing » Ident(voi) _Gem) and unnaturalness (OCP(voi)) co-reside within a single module.