The effect of a concurrent task on Parkinsonian speech.

The aim of the study was to examine the role of attention in Parkinsonian speech control, by using a dual-task paradigm. Whilst it is well-known that skeletal motor performance is impaired when Parkinson's disease (PD) patients are required to perform two motor acts simultaneously, this has not been examined in the context of speech motor control. Fifteen idiopathic PD patients and matched controls performed two speech tasks (spontaneous conversation and numerical recitation), with and without simultaneous engagement on a visuo-manual tracking task. Volumetric and temporal parameters of speech control were examined. The findings show a trend towards reduced overall speech volume, and a significant increase in progressive volume decay for patients relative to controls, for the concurrent task condition. Patients' speech was also characterised by increased speech initiation time and pause time, while speech rate was reduced upon introduction of the concurrent task. Performance on the visuo-motor task by patients, however, was similar to that of controls. The PD patients demonstrated a deterioration of volumetric and temporal measures of speech motor control, when attentional resources were reduced by a distractor task. Consistent with dual-task studies of skeletal movement control, these findings also show that there is a Parkinsonian disadvantage for the more automatic and non-visually controlled task, that is, speech, in the present study. It is, therefore, suggested that speech and skeletal movement control are similarly driven by the higher-order frontostriatal impairment inherent in PD.