Phonation in verbal tics and true words is distinguishable on the basis of voice quality

Abstract

Adults with Tourette syndrome produce vocal tics that mimic true words and phrases. These verbal tics often occur while the ticcer is actively engaged in speaking. By virtue of their isomorphism with true words, co-speech verbal tics can introduce unintended meanings into a talker's utterances. How does the ticcer-talker compensate for the presence of intrusive verbal tics that threaten to confuse their interlocutor? In the present study, the acoustics of phonation in naturalistic co-speech ticcing by four adult speakers of English was examined. Six acoustic parameters previously identified as indices of the distinction between falsetto and modal voice were extracted from ticced and spoken stressed vowel and whole-word intervals. For all participants, at least three out of the six markers of falsetto were observed in verbal tics and were absent in true words. Furthermore, transitions into and out of falsetto were concomitant with transitions across speech-tic and tic-speech junctures, respectively. These results suggest that phonation tasks for verbal tics are aimed at achieving falsetto mode of laryngeal vibration, in contrast to phonation in spoken English, which is largely modal. Findings are interpreted in terms of a discourse-level task that organizes ticced and spoken vocalizations in the service of clear communication.