Effects of Strategies on Mental Rotation and Hemispheric Lateralization: Neuropsychological Evidence Barbara Tomasino and Raffaella I. Rumiati Abstract & We can predict how an object would look if we were to see it from different viewpoints by imagining its rotation. This essential human ability, called mental rotation (MR), guides individuals’ actions by constantly updating their environmental consequences. It is, however, still under debate whether the way in which our brain accomplishes this operation is deter- mined by the type of stimulus or rather by a mental strategy. Here we present neuropsychological evidence sustaining the view that what matters is the type of strategy adopted in MR. Thus, independently of the type of stimulus, patients with left hemisphere lesions showed a selective deficit in MR as a consequence of their manual activity, whereas patients with right hemisphere lesions were found impaired in MR by means of a visual strategy. We conclude that MR is achieved by recruiting different strategies, implicitly triggered or prompted at will, each sustained by a unilateral brain network. & INTRODUCTION Typically, mental rotation (MR) is studied by asking subjects to decide whether two images—of which one is either a mirror or an identical rotated image of the other—are the same or different (Corballis, 1997; She- pard & Metzler, 1971; Shepard & Cooper, 1982). The analysis of the response times (RTs) shows that subjects create an internal image of an object and that they rotate it until it is congruent with the target object. A linear increase in RTs with increasing angular disparity is usu- ally found for rotated stimuli such as two-dimensional alphanumeric characters (Corballis & Sergent, 1989) and three-dimensional Shepard and Metzler’s stimuli (Cohen et al., 1996; Shepard & Metzler, 1971; Shepard & Coo- per, 1982). MR operations can be distinguished accord- ing to the type of stimulus involved (Tomasino, Toraldo, & Rumiati, 2003; Rumiati, Tomasino, Vorano, Umilta `, & DeLuca, 2001; Kosslyn, DiGirolamo, Thompson, & Al- pert, 1998), the reference frame (Zacks, Rypma, Gabrieli, Tversky, & Glover, 1999; Zacks, Mires, Tversky, & Ha- zeltine, 2000; Zacks, Ollinger, Sheridan, & Tversky, 2002; Wraga, Creem, & Proffitt, 1999), or the strategies used (Kosslyn, Thompson, Wraga, & Alpert, 2001). As far as the stimulus type is concerned, different operations may be recruited in MR depending on whether the stimulus type is a body part or a two- or three-dimensional object. Neuropsychological studies indicate that these two types of transformations can be selectively affected. For instance, a patient with left hemisphere (LH) brain damage was described as being selectively impaired when deciding whether a hand is left or right despite being still able to mentally rotate Shepard and Metzler’s stimuli (Rumiati et al., 2001). On the other hand, a patient (JB) with a bilateral infero- temporal lesion was reported as having a deficit in per- forming MR of Shepard and Metzler’s stimuli (Sirigu & Duhamel, 2001). However, JB’s ability to mentally rotate motor images of body parts was not investigated. Nor was this ability assessed in other posterior left (Morton & Morris, 1995; Metha & Newcombe, 1991; Kosslyn, Holtzman, Farah, & Gazzaniga, 1985) or right (Bricolo, Shallice, Priftis, & Meneghello, 2000; Ditunno & Mann, 1990; Farah & Hammond, 1988; Ratcliff, 1979) brain-damaged patients who have also been described as having a deficit of MR operations. In a recent study (Tomasino et al., 2003), a direct comparison between right hemisphere (RH) and left hemisphere (LH) pa- tients’ performance on MR of both types of stimuli showed that lesions in the LH impaired MR of hands, while lesions in the RH affected MR of external objects (e.g., a puppet and flag shapes). Psychophysical studies indicate that different mecha- nisms may be selected in MR according to the frame of reference used for the rotation (Zacks et al., 2000). Thus, MR can be accomplished taking as a reference frame the object itself (i.e., allocentric view) or the viewer’s (i.e., egocentric view). It has been shown that the allocentric and egocentric transformations lead to different chronometric patterns. A strong correlation between the angle of rotation and RTs has been consist- ently obtained in subjects who mentally rotated the stimuli using the allocentric view (Zacks et al., 1999, 2000, 2002; Wraga et al., 1999; Corballis, 1997; Shepard Scuola Internazionale Superiore di Studi Avanzati (SISSA) D 2004 Massachusetts Institute of Technology Journal of Cognitive Neuroscience 16:5, pp. 878–888