MOTOR SPEECH ADAPTATION: AN ACOUSTIC STUDY OF TEMPORAL AND SPECTRAL RESPONSE PATTERNS IN SUBJECTS WITH FOCAL, CORTICAL LESION

Studies reported here explore the speech-production skills of a group of American veterans who sustained focal, cortical lesions to the right or left hemisphere during the Vietnam confrontation. Temporal and spectral characteristics of speech production were examined under two speaking conditions: a normal, or control, condition and an experimental condition which used an appliance to restrict mandibular participation during speech. The purpose of the study was twofold: first, to provide a quantitative analysis of the similarities and differences in temporal and spectral characteristics of speech following a circumscribed lesion to either the right or left hemisphere; and second, to investigate the strategies available to speakers with cortical lesions adjust, or accommodate, to changes in peripheral, oral-structure relationships. Analyses of temporal and spectral characteristics of speech in these two conditions provided quantitative information related to structure-function questions commonly addressed in the clinical literature regarding speech disorders in cortically injured patients.;Comparable formant frequency and duration values are not produced by Control subjects in normal and restricted-jaw speaking. Control subjects produce slightly higher F(,1) and significantly lower F(,2)-F(,3) frequencies during restricted-jaw conditions. Moreover, Control subjects use a temporal strategy of generalized slowing of articulation to assist in optimizing their response to abnormal peripheral conditions. Data from Control subjects suggest the motor speech system uses a range of articulator positions to produce contextual speech under normal and abnormal peripheral conditions. Temporal relationships of gestures are retained by Control subjects during abnormal peripheral conditions suggesting gesture timing may be inherent to phonological representations.;Cortically injured subjects use a slightly different set or range of articulator positions to adjust area/length relationships in the vocal tract than Control subjects, regardless if speaking is under normal or restricted-jaw conditions. Frequency and duration response patterns during restricted-jaw speaking suggest motor-speech systems of cortically injured speakers are less flexible and more heavily influenced by contextual frameworks. Taken overall, frequency- and duration-response patterns indicate cortically injured speakers have difficulty integrating spatio-temporal information underlying articulatory maneuvers during normal- and abnormal-peripheral conditions.