Liquids are unique in their ability to occupy syllable onset, nucleus, and coda positions in American English, as well as the fact that they are composed of two lingual gestures. Upon inspection of /l/ in syllable nucleus and coda positions using real-time MRI, it appears that the tongue tip constriction we might expect for /l/ is often not present, a phenomenon called /l/-vocalization. However, it is not merely the case that the consonantal gesture of /l/ is completely lost in these syllable positions, leaving behind a simple vocalic configuration. Though there is often no raising of the tongue tip in an attempt to make contact with the alveolar ridge, the /l/ exhibits complex tongue shaping involving curling in the region of the tongue blade. The result is a lowered tongue blade relative to the tongue tip and dorsum. This shaping is captured through measures of Gaussian curvature at evenly spaced points along the tongue. The results indicate that /l/-vocalization in the syllable rhyme does not involve a complete loss of the consonantal nature of the lateral, but rather a modification of its realization.
Bibliographic reference. Smith, Caitlin / Lammert, Adam (2013): "Identifying consonantal tasks via measures of tongue shaping: a real-time MRI investigation of the production of vocalized syllabic /l/ in American English", In INTERSPEECH-2013, 3230-3233.