Disruptions of Advance Speech Programming in Ataxic Dysarthria

K Spencer, M Rogers

 

The dysarthrias have traditionally been thought to result from a disruption of motor speech execution.  However, individuals with ataxic dysarthria could manifest processing abnormalities before speech execution occurs.  This hypothesis is consistent with neurophysiology and limb motor control research which suggests involvement of the cerebellar control circuit in the programming of movement.  Five speakers with ataxic dysarthria, fifteen control participants and ten participants with hypokinetic dysarthria completed a speech reaction time protocol designed to capture whether utterances are fully programmed at speech onset.  The protocol took advantage of robust length-dependent changes in reaction time that occur when producing utterances of varying length and complexity.  This “sequence length effect” was evidenced by the control participants and most participants with hypokinetic dysarthria.  However, the speech reaction times of several participants with ataxic dysarthria did not increase linearly with an increase in utterance length.  These results suggest that speakers with ataxic dysarthria have difficulty with advance programming.  One explanation of the reduced sequence length effect may be deficient use of feedforward information, which subsequently precludes complete programming of the utterance prior to execution.