Fundamental frequency (F) attributes in the speech of Wernicke's aphasics

Abstract

Adult aphasics with localized posterior lesions of the left cerebral hemisphere (Wernicke's aphasics) were examined for deficits in F0 attributes during sentence production. Clinically, such patients are diagnosed as having primary deficit in speech comprehension, with relatively intact articulation. While their spoken utterances exhibit a normal range of F0 values, experimental testing reveals impairment in the production of selected F0 attributes that are influenced by sentential factors. In this study, patients read aloud sentences that had been designed to test sentential properties of F0 in normal speech. Computer-aided acoustical analysis of F0 indicated that normal speakers produce higher F0 values at the beginnings of long versus short single-clause sentences. A corresponding analysis of aphasic utterances for the same sentence materials indicated that these patients produce similar starting values of F0 for sentences of different lengths. In normal speech, the F0 values generally decline throughout the course of a main clause in a declarative sentence, with optional resetting of the declination function at major syntactic boundaries. For Wernicke's speech, a similar pattern of declination was observed, except that resetting accompanied minor as well as major syntactic boundaries, suggesting that the patients program F0 attributes over shorter-than-normal domains. Finally, word substitution errors committed by the Wernicke's aphasics did not perturb the F0 attributes exhibited in their speech, suggesting that the programming of these F0 characteristics proceeds independently of lexical selection. The Wenicke's deficits are discussed in terms of a model of speech planning and execution. [Supported by NIH Grants NS 11408, NS 13028, and the MIT Research Laboratory of Electronics.]