Voice onset time in aphasia: Thai. II. Production

The aim of this study was to investigate voice onset time (VOT) production in homorganic word-initial stops in Thai in order to explore the nature of speech production deficits across clinical varieties of aphasia. Thai exhibits a three-category distinction in bilabial (/b,p,ph/) and alveolar (/d,t,t,h/) stops, and a two-category distinction in velar (/k,kh/) stops. Subjects included three Broca asphasics, one transcortical motor asphasic, two global asphasics, one conduction aphasic, one Wernicke aphasic, one nonaphasic dysarthric patient, one right-brain-damaged patient, and five normal controls. Test stimuli consisted of eight monosyllabic real words. The results of VOT measurements indicated that Broca and global asphasics exhibited a more severe production disorder than Wernicke, conduction, or transcortical motor asphasics. The right-brain-damaged patient showed no impairment in VOT production. Comparisons are drawn to earlier studies of VOT production in aphasia in two-category languages. Issues concerning the underlying basis of the production deficit for nonfluent aphasics, fluent aphasics, and nonaphasic dysarthrics as well as the relation between perception and production of VOT are discussed.