The (inter)dental approximant is a little-studied speech sound in the Philippines and Western Australia. In this paper, we document the articulation of the sound, providing acoustic and video data from Kagayanen and Limos Kalinga, respectively. The sound is attested in at least fifteen languages. It is contrastive in five Western Australian languages, while in the Philippines it generally patterns as an allophone of /l/ but has emerged recently as a separate phoneme due to contact. It arose independently in the two regions. The sound is easily describable in terms of values of phonological features or phonetic parameters. All of these factors argue for the inclusion of the sound in the International Phonetic Alphabet.
Kenneth S. Olson, Jeff Mielke, Josephine Sanicas-Daguman, Carol Jean Pebley and Hugh J. Paterson (2010) The phonetic status of the (inter)dental approximant. Journal of the International Phonetic Association, 40.2 , pp. 199-215. doi:10.1017/S0025100309990296
Comments: My contribution in this collective work involved extensive library research, the collection of sources, translation of sources, and evaluating the personal un-published field notes of previous scholars. Encouraged in the historical comparative work by Ken Olson, I suggest that there is enough evidence to support the idea that the interdental approximant is a retention, rather than independent innovations. My research work on this topic resulted in me presenting two additional academic presentations. See the interdental approximant project description for further details.
Other works on the interdental approximant:
Mielke, Jeff, Kenneth S. Olson, Adam Baker & Diana Archangeli. 2011. Articulation of the Kagayanen interdental approximant: An ultrasound study. Journal of Phonetics 39(3). 403–412. DOI: http://dx.doi.org/10.1016/j.wocn.2011.02.008
Olson, Kenneth S., Emy T. Ballenas & Nilo M. Borromeo. 2009. Buhi’non (Bikol) digital wordlist: Presentation form. Language Documentation & Conservation 3(2). 213–225. URI: http://hdl.handle.net/10125/4440
Olson, Kenneth S., Glenn Machlan & Nelson Amangao. 2008. Minangali (Kalinga) digital wordlist: Presentation form. Language Documentation & Conservation 2(1). 141–156. URI http://hdl.handle.net/10125/1772
Olson, Kenneth S. & Jeff Mielke. 2008. Acoustic properties of the interdental approximant in Kagayanen. Journal of the Acoustical Society of America 123(5). 3460. DOI http://dx.doi.org/10.1121/1.2934307
Matthew Harley (2012) Unusual sounds in Nigerian languages. In Advances in Minority Language Research in Nigeria Part I (eds.) Roger M. Blench and Stuart McGill. Kay Williamson Educational Foundation African languages Monographs No. 5. pages: 38-65. Rüdiger Köppe Verlag: Köln