Effects of transitory lingual nerve impairment on speech: an acoustic study of diphthong sounds

The effects of lingual nerve impairment on the phonetic quality of diphthongs were studied by analyzing changes in their main acoustic features when anesthetic was injected into the lingual nerve to partly block the normal neural feedback mechanisms in speech.

The speech material consisted of 8 diphthongs in word context produced by 7 male speakers. Every utterance was repeated 10 times using normal speech rate and intonation with and without the anesthesia (Ultracain D-Suprarenin, 0.8 mL; Aventis Pharma Deutscland GmpH, Frankfurt am Main, Germany). In addition, 1 male speaker with permanent nerve impairment was studied. The acoustic features (F1, F2, F0, and duration) were analyzed using Computerized Speech Laboratory (CSL 4300B; Kay Elemetrics, Lincoln Park, NJ).

At the group level, no general significant acoustic changes were found between the 2 conditions. The changes were highly individual and variable across the subjects. Significant changes were observed for all the subjects, most prominently for the subject with permanent nerve impairment.

According to the results, lingual nerve impairment has effects on the production of diphthongs. A comparison between monophthongs and diphthongs showed that the alterations are more significant for the diphthongs than for other vowels indicating the more demanding, complicated, and complex manner of articulation of diphthongs.