Routes to action: Evidence from apraxia

Abstract

We report the case of a right-handed patient (CD), with a unilateral lesion of the left parietal lobe, who was unimanually apraxic to visually presented objects. In particular, CD was unable to initiate learned gestures to seen objects with his right hand, even though he was able to perform the same gestures with his left hand (and was often able to perform right-hand gestures subsequently). CD could perform right-handed gestures when the objects were not present and he was given their names, and his performance with seen objects improved when he was given pairs of objects. From CD's performance we argue that gestures to visually presented objects are normally based on co-operation between stored knowledge about the class of gesture to use, and directly computed visual representations that provide the spatial co-ordinates for action. We suggest that CD's problem is due to his having an impaired “route” from vision to action that selectively impairs right-hand actions for him.