An MRI-based articulatory and acoustic study of lateral sound in American English

The production of the lateral sounds generally involves a linguo-alveolar contact and one or two lateral channels along the parasagittal sides of the tongue. The acoustic effect of these articulatory features is not clearly understood. In this study, we compare two productions of /l/ in American English by one subject, one for a dark /l/ and the other for a light /l/. Three-dimensional vocal tract models derived from the magnetic resonance images were analyzed. It was shown that zeros in the vocal tract acoustic response are produced in the F3-F5 region in both /l/ productions, but the number of zeros and their frequencies are affected by the length of the linguo-alveolar contact and by the presence or absence of lateral linguopalatal contacts. The dark /l/ has one zero below 5 kHz, produced by the cross mode posterior to the linguo-alveolar contact, while the light /l/ has three zeros below 5 kHz, produced by the asymmetrical lateral channels, the supralingual cavity and the cross mode posterior to linguo-alveolar contact.