KINEMATIC ANALYSIS OF MOVEMENT IMITATION IN APRAXIA

Accuracy of the final position and kinematics of movement were analyse d during the imitation of meaningless gestures in patients with unilat eral brain lesions who performed with the hand ipsilateral to the lesi on and in control subjects. Controls imitated the gestures virtually w ithout spatial errors. The kinematics of their movements was character ized by single-peaked and approximately bell-shaped velocity profiles of the transport phase combined with no or only minor corrective movem ents in the final phase. Patients with right brain damage (RED) perfor med as well as control subjects with respect to both spatial accuracy of final hand-positions and kinematic parameters of the movement traje ctories. Patients with left brain damage (LED) committed spatial parap raxias and had a much higher frequency of kinematic abnormalities. How ever there was no correlation between kinematic abnormalities and apra xic errors. There were kinematically abnormal movements which reached a correct final position as well as kinematically normal movements lea ding to apraxic errors. One possible explanation for the combined occu rrence of kinematic abnormalities and parapraxias in LED patients woul d be that they are independent sequels of left hemisphere lesions. An alternative account is that the associations and dissociations result from an interaction between one common basic deficit and strategies to cope with this deficit. The basic deficit may concern the mental repr esentation of the target position. The LED patients may react to the a bsence of an appropriate representation of the target by one of two al ternative strategies; they may switch to a strategy of slowed, on-line controlled movements to find the required final position, or they may move their hand smoothly at normal speed to a roughly specified locat ion without taking note of their deficiency. Depending on whether thes e strategies are successful or not they would lead to the observed ass ociations and dissociations between kinematic abnormalities and spatia l parapraxias.