Acquired dysarthria within the context of the four-level framework of speech sensorimotor control

The Four-Level Framework of speech sensorimotor control (Van der Merwe, 1997) complicates the traditional view of dysarthria as a purely motor execution disorder. According to this framework, hypokinetic, hyperkinetic and ataxic dysarthria are programming-execution dysarthrias, while flaccid dysarthria is the only execution dysarthria. This preliminary study aimed to differentiate programming-execution dysarthria from execution dysarthria by examining variability of the temporal control of speech. Six participants and five control participants repeated 15 stimulus words ten times. Voice onset time, vowel duration, vowel steady state duration and vowel formant transition duration were measured acoustically. The coefficient of variation of the temporal parameters, and the correlation coefficient between the durational parameters, were calculated and analysed using descriptive statistics. The coefficient of variation revealed that the speakers with dysarthria were more variable than the control speakers. All participants, except those with flaccid dysarthria, showed similar patterns of intra-subject variability. Those with flaccid dysarthria exhibited greater intra-subject variability of voice onset time. The correlation analysis did not reveal differences between dysarthria type, or between the dysarthric speakers and the controls. Differences found in the patterns of variability may support the hypothesis that individuals with programming-execution dysarthria resort to a different level of control than those with execution dysarthria. Further research in this field is necessary.