Locus of Functional Impairment in the Production of Speech Rhythm after Brain Damage: A Preliminary Study

Abstract

This acoustic-perceptual, multiple-case study of the Rhythm Rule (RR) in English, a phonological phenomenon whereby adjacent stresses are adjusted to avoid “stress clash” (e.g.,thirTEENvsTHIRteen MEN), was undertaken to identify the locus of functional impairments in speech prosody in different aphasic syndromes. Subjects included two left brain-damaged aphasic patients (1 fluent, 1 nonfluent), one right brain-damaged nonaphasic patient, and one nonneurological control. They were instructed to read sentences including experimental (bisyllabic “double-stressed” words) and matching control (bisyllabic “initial-stressed” words) phrases of increasing length. Results of acoustic and perceptual measures indicated that rhythmic disturbances associated with the RR emerged regardless of lesion site. The locus of functional impairment was isolated to phonetic implementation of the RR, as opposed to either loss of word-level stress or loss of the RR. Findings suggest that neural substrates of speech prosody are broadly distributed in the left and right cerebral hemispheres.