Disfluency: it is not always stuttering (2013)

To the Editor: Disfluency refers to normal, abnormal, or ambiguous breaks in the continuity of producing phonologic, lexical, morphologic, and/or syntactic language units in oral speech 1. It appears to be common in neurofibromatosis type 1 (NF1) and has been variously described as reduced or fast rate 2-4, deliberate paced rhythm 5, irregularities in speech rate and rhythm 6, sloppy or labored articulation 4, and stuttering 6. These divergent findings generally resulted from perceptual studies which, except for Alivuotila et al. 4, did not include control participants. Therefore, to further delineate disfluency in NF1, we calculated the frequency of disfluencies and measured speaking rate in a group of NF1 patients and controls, and looked for similarities with known fluency disorders. Patients were 30 NF1 adults, 15 males and 15 females, fulfilling the National Institutes of Health (NIH) diagnostic criteria for NF1. Controls included 30 age- (p > 0.05) and gender-matched adults (p > 0.05) without NF1 who did not have speech-language disorders. Selected fragments from video-recorded spontaneous speech were subjected to an in-depth fluency analysis (Table S2, Supporting information). Disfluencies were classified as ‘stutter-like disfluencies’ (part-word repetitions, single-syllable word repetitions, and disrhythmic phonations) or ‘other disfluencies’ (interjections, revisions/abandoned utterances, and multisyllable/phrase repetitions) 7 and their frequency of occurrence was determined. Speaking rate was measured as both speech and articulation rate (i.e. the number of syllables per second with and without inclusion of pause intervals, respectively). Additionally, pauses were analyzed according to their number and duration, and a measure of articulation rate variation was calculated. The latter can be associated with the occurrence of rapid bursts of speech. Statistical analysis for comparison of NF1 patients and controls included two-way analyses of variance with ‘group’ and ‘gender’ as fixed factors (α = 0.05). As interaction terms were not significant, main effects were interpreted directly. Results (Table 1) showed that differences between NF1 adults and controls were especially marked for speaking rate. NF1 adults had a faster articulation rate, showed more articulation rate variation, and paused more and longer than controls. However, speech rate was similar between groups. Given the faster articulation rate, this seems contradictory, but can readily be explained. Speech rate is a function of articulation rate and pausing. As NF1 adults also paused more and longer, the effect of the faster articulation rate was counterbalanced, and speech rate appeared normal. Additionally, NF1 adults displayed less interjections than controls, but multisyllable/phrase repetitions occurred more in NF1 males than in male controls. Among the fluency disorders, stuttering is the most familiar one. Stuttering refers to speech events that contain monosyllabic whole-word repetitions, part-word repetitions, sound prolongations, or blockages which may be accompanied by accessory (secondary) behaviors 1. Although three NF1 participants (10%) fit that description, it is not likely that NF1 adults as a group exhibit stuttering because their frequency of stutter-like disfluencies was not significantly different from that of the controls. However, as the prevalence of stuttering in the general population is estimated at 1%, it is possible that stuttering occurs with a higher frequency in NF1. Another, less known fluency disorder, is cluttering, which is characterized by a fast and/or irregular rate together with at least one of the following: an excessive number of other disfluencies, inappropriate coarticulation, and abnormal pausing or stress placement 8. Although the frequency of other disfluencies did not differ significantly between NF1 adults and controls, the present findings (faster and more varied articulation rate and more and longer pauses) and those of Alivuotila et al. 4 (sloppy or labored articulation) suggest that the disfluency pattern displayed by NF1 adults resembles cluttering more than stuttering. Alternatively, it is possible that the pattern observed is syndrome-specific and different from both stuttering and cluttering. Research comparing the speech of NF1 patients with that of stutterers, clutterers, and individuals with other genetic syndromes is needed. This work was made possible through funding from the Research Foundation Flanders (FWO). We would also like to thank Prof Dr Paul Corthals for developing some Praat scripts which allowed semiautomated measurements. M Cosynsa Y van Zaalenb,c G Mortierd,e S Janssensd A Ameza J Van Dammea J Van Borsela,f aDepartment of Otorhinolaryngology and Logopaedic-Audiological Sciences Ghent University Ghent, Belgium bDepartment of Health Care & Technology for Quality of Life Fontys University of Applied Sciences Eindhoven, the Netherlands cCenter of Speech, Language and Fluency Disorders Amersfoort, the Netherlands dCenter for Medical Genetics Ghent University Hospital Ghent, Belgium eCenter for Medical Genetics Antwerp University Hospital Edegem, Belgium, and fVeiga de Almeida University Rio de Janeiro, Brazil Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.