Sensory feedback dependence hypothesis in persons who stutter Aravind Kumar Namasivayam a, * , Pascal van Lieshout a,b,c,d , William E. McIlroy b,e,f , Luc De Nil a,g a Department of Speech-Language Pathology, Oral Dynamics Laboratory, University of Toronto, 160-500 University Avenue, Toronto, Ontario, Canada M5G 1V7 b Toronto Rehabilitation Institute, 550 University Avenue, Toronto, ON, Canada M5G 2A2 c Institute of Biomaterials and Biomedical Engineering, Rosebrugh Building, 164 College Street, Room 407, University of Toronto, Toronto, ON, Canada M5S 3G9 d Department of Psychology, Human Communication Laboratory, CCT Building, 4th Floor, 3359 Mississauga Road North, Mississauga, ON, Canada L5L 1C6 e Graduate department of rehabilitation science and department of physical therapy Rehabilitation Sciences Building, 160-500 University Avenue, Toronto, ON, Canada M5G 1V7 f Department of Kinesiology, University of Waterloo, 200 University Avenue, West Waterloo, ON, Canada N2L 3G1 g Toronto Western Research Institute, University Health Network, 399 Bathurst Street, Toronto, ON, Canada M5T 2S8 article info Article history: Available online 18 August 2009 PsycINFO classification: 3270 2221 2330 Keywords: Stuttering Coordination Sensory feedback Perturbation abstract The present study investigated the role of sensory feedback (audi- tory, proprioception, and tactile) at the intra- and inter-gestural levels of speech motor coordination in normal and fast speech rate conditions in two groups: (1) persons who stutter (PWS) and (2) those who do not (PNS). Feedback perturbations were carried out with the use of masking noise (auditory), tendon vibration (propri- oception), and nonwords that differed in the amount of required tactile lip contact (/api/ + tactile and /awi/ À tactile). Comparisons were also made between jaw-free and jaw-immobilized (with a bite-block) task conditions. It was hypothesized that if PWS depend more strongly on sensory feedback control during speech production, they would show an increase in variability of move- ment coordination in the combined presence of fast speech rates and feedback perturbations, in particular, when jaw motions are blocked and adaptations in the other articulators are required to achieve the task goals. Significant feedback perturbation effects were found for both groups, but the only significant between-group effect was found at fast speech rates in the jaw-free condition, showing that control 0167-9457/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.humov.2009.04.004 * Corresponding author. Tel.: +1 416 946 8552; fax: +1 416 978 1596. E-mail address: a.namasivayam@utoronto.ca (A.K. Namasivayam). Human Movement Science 28 (2009) 688–707 Contents lists available at ScienceDirect Human Movement Science journal homepage: www.elsevier.com/locate/humov