Linguolabials, or more specifically apicolabials and laminolabials, are consonants articulated by placing the tongue tip or blade against the upper lip, which is drawn downward to meet the tongue. They represent one extreme of a coronal articulatory continuum that extends from labio-lingual to subapical-palatal places of articulation. Cross-linguistically, linguolabial consonants are very rare. They are found in a cluster of 17 Southern Oceanic languages in Vanuatu, in the Kajoko dialect of Bijago in Guinea-Bissau, in UmotÃÂna (a recently extinct Bororoan language of Brazil), and as paralinguistic sounds elsewhere, such as 'expressive' words in Mochi Chaga. They are also relatively common in disordered speech, and the IPA diacritic is specifically provided for in the extensions to the IPA, as it is otherwise rare enough that speech pathologists might be unaware of it.
Linguolabials are produced by constricting the airflow between the tongue and the upper lip. They are attested in a number of manners of articulation including stops, nasals, and fricatives.
Linguolabial consonants are transcribed in the International Phonetic Alphabet with the "seagull" diacritic, , or potentially the same diacritic above, , if the letter has a descender.
Transcription is inconsistent. The seagull diacritic was adopted by the IPA at the Kiel Convention in 1989. It was to be used on alveolar consonant letters. Only were illustrated, but if the 'alveolar' instruction were followed, the consonant series would be written . This notation is seen in a number of sources. However, linguolabial fricatives are not sibilants, and in the extIPA chart in the IPA Handbook of 1999, they are illustrated on dental letters, making the series . This notation is also seen in a number of sources; indeed some, such as , employ both. More recently, official IPA transcription has used it on labial letters: . The choice of the base consonant may depend on whether the author analyses the linguolabial as being phonologically labial or alveolar.
Twenty years before Kiel, the IPA had transcribed such sounds with the (yet-to-be-approved) apical diacritic, , on a labial letter, with the analysis of these sounds as apico-labial. However, state that this solution is 'unsuitable' because the articulation of linguolabials may be either apical or laminal.
==== By analogy of the distinction made between labiodentals and dentolabials, labiolinguals may be distinguished as consonants articulated by touching the tongue to the lower lip. Such sounds could conceivably be distinguished by placing the diacritic above the letter, as with dentolabials, but that is not an established convention.
In Vanuatu, some of the SantoâÂÂMalekula languages have shifted historically from bilabial to alveolar consonants via an intermediate linguolabial stage, which remains in other Santo and Malekula languages.
While labials have become linguolabial before nonrounded vowels in various languages (e.g. Tangoa, Araki, Nese), the sound shift went further in languages such as Tolomako, which shifted the linguolabials to full alveolar consonants: *b > *[p] > pÃÂ > t [t]; *m > mÃÂ > n [n]. Thus, POc *bebe > (spelled in Tangoa or in Araki) later became in Tolomako. Likewise, POc *tama > (cf. Tangoa , Araki ) > Tolomako .
However, in several languages linguolabials are shifting back to bilabial, namely in Tutuba, Vüënen Taut, Tangoa, Mavüea.
Languages that have linguolabials as ordinary speech sounds: