Selective deficit of motor imagery as tapped by a left–right decision of visually presented hands

This paper presents the case of MT, a patient suffering from apraxia with left-hemisphere damage who showed a selective deficit in mentally rotating images of hands whereas he was still able to mentally rotate other visual stimuli. The deficit was particularly evident when MT was asked to decide which hand (left or right) was represented in a picture. Parsons (1987, 1994) suggested that in order to carry out this task, participants would mentally rotate a representation of their own body part until it aligns with the stimulus and it does appear that MT’s ability to mentally simulate movements is impaired. In contrast, he was able to mentally rotate other forms of bi- and three-dimensional stimuli. Our findings are also consistent with Kosslyn, Digirolamo, Thompson, and Alpert’s (1998) proposal that there are at least two ways in which objects can be mentally rotated, one that recruits processes devoted to motor preparation (e.g., hands), and another that does not.