Effect of sentence length on the production of linguistic stress by left- and right-hemisphere-damaged patients

An acoustical/perceptual study of phonemic stress (e.g., HOTdog vs, hot DOG ) was conducted to evaluate the effect of sentence length on stress product ion after brain damage. Productions of phonemic stress pairs were elicited in sentence contexts of increasing length from eight left-hemisphere-damage d nonfluent (LHD-NFL), fluent LHD-FL), right-hemisphere-damaged (RHD), and normal speakers (n = 32). Tape recordings of subjects' productions were pre sented to naive listeners for perceptual identification of stress placement . Acoustic analysis focused on fundamental frequency, duration, and intensi ty of the initial and final syllables as well as pause duration between syl lables. Perceptual tests indicated that regardless of sentence length, all brain-damaged groups exhibited an impairment in the production of linguisti c stress when compared to normals. The LHD-NFL group experienced the greate st difficulty in signaling stress contrasts, followed in order by the LHD-F L and RHD groups. In medium-length sentences, the LHD-R. group's performanc e was degraded by comparison to short-length sentences. Acoustic analysis s howed that pause duration was the strongest predictor of phonemic stress fo r all groups. Acoustic profiles of the RHD group were similar qualitatively to those of normals, but differed quantitatively in terms of magnitude of effect associated with shifts in stress patterns. Findings are brought to b ear on the nature of the stress production deficit after unilateral brain d amage, the role of the right hemisphere in linguistic prosody, and the conc ept of "subtle phonetic deficit" in fluent aphasia. (C) 1999 Academic Press .