These are normally used with vowels, but may occur with consonants. For example, in the Athabaskan language Hupa, voiceless velar fricatives distinguish three degrees of labialization, transcribed either or . The extensions to the IPA has two additional symbols for degrees of rounding: Spread and open-rounded (as in English). It also has a symbol for labiodentalized sounds, . If precision is desired, the Abkhaz and Ubykh articulations may be transcribed with the appropriate fricative or trill raised as a diacritic: , , , . For simple labialization, resurrected an old IPA symbol, , which would be placed above a letter with a descender such as . However, their chief example is Shona sv and zv, which they transcribe and but which actually seem to be whistled sibilants, without necessarily being labialized. Another possibility is to use the IPA diacritic for rounding, distinguishing for example the labialization in English soon and swoon. The open rounding of English is also unvelarized. Assimilation Labialization also refers to a specific type of assimilatory process where a given sound become labialized due to the influence of neighboring labial sounds. For example, may become in the environment of , or may become in the environment of or . In the Northwest Caucasian languages as well as some Australian languages rounding has shifted from the vowels to the consonants, producing a wide range of labialized consonants and leaving in some cases only two phonemic vowels. This appears to have been the case in Ubykh and Eastern Arrernte, for example. The labial vowel sounds usually still remain, but only as allophones next to the now-labial consonant sounds. Examples See also Labio-palatalization (◌ᶣ) References Bibliography Crowley, Terry. (1997) An Introduction to Historical Linguistics. 3rd edition. Oxford University Press. Assimilation (linguistics) Secondary articulation