From: "Marcus Smith"
> >> All native and non-native speakers I've had contact with
> >> agree that they seem to appear predictably between unvoiced
> >> consonants, or in final position after an unvoiced consonant.
> >>
> >Do they become voiceless even if they're stressed?
>
> The standard treatment say devoicing only applies to /i/ and /u/, but I've
> heard it used with /a/ as well. They devoice when they are not next to a
> voiced sound. They do not devoice if they are word initial or accented.
Some
> dialects delete the vowels rather than devoice them.
I don't recall having heard it with /a/, but /o/ occurred in the name Kyoto
(pronounced "Kyot'") (rarely).
Kou