Acoustic analyses of two recovered cases of foreign accent syndrome

Abstract

Recently, a growing number of studies have been published involving phonetic and acoustic analyses on the rare motor-speech disorder known as Foreign Accent Syndrome (FAS). These studies have relied on pre- and post-trauma speech samples to investigate the acoustic and phonetic properties of individual cases of FAS speech. This study presents detailed acoustic analyses of the speech characteristics of two new cases of FAS using identical pre- and post-recovery speech samples, thus affording a new level of control in the study of Foreign Accent Syndrome. Participants include a 48-year-old female who began speaking with an “Eastern European” accent following a traumatic brain injury, and a 45-year-old male who presented with a “British” accent following a subcortical cerebral vascular accident (CVA). The acoustic analysis was based on 18 real words comprised of the stop consonants /p/, /t/, /k/; /b/, /d/, /g/ combined with the peripheral vowels /i/, /a/ and /u/ and ending in a voiceless stop. Computer-based acoustic measures included: (1) voice onset time (VOT), (2) vowel durations, (3) whole word durations, (4) first, second and third formant frequencies, and (5) fundamental frequency. Formant frequencies were measured at three points in the vowel duration: (a) 20%, (b) 50%, and (c) 80% to assess differences in vowel ‘onglides’ and ‘offglides’. The acoustic analysis allowed precise quantification of the major phonetic features associated with the foreign quality of participants' FAS speech. Results indicated post-recovery changes in both duration and frequency measures, including a tendency toward more normal VOT production of voiced stops, changes in average vowel durations, as well as evidence from formant frequency values of vowel backing for both participants. The implications of this study for future research and clinical applications are also considered.

Keywords:

• Foreign accent syndrome
• Brain injury
• Acoustic analysis
• Formant frequencies
• Voice onset time
• Vowel duration