On the different mechanisms of spatial transpositions: a case of representational allochiria in clock drawing.

In the present paper, we describe a neglect patient who showed allochiria in copying and drawing a clock from memory. To verify the mechanisms of allochiria in our patient, we designed an experimental investigation including two conditions: to write single hours and to copy their spatial locations, one at a time onto blank circles. The patient showed spatial transpositions in writing hours on blank dials, but did not show allochiria in the reproduction of spatial locations. These findings suggest that the patient could not represent in her mind appropriate spatial coordinates of each hour with respect to the whole clock face. These data are in contrast with findings reported in other patients and demonstrate that constructional allochiria associated with spatial neglect may derive from different causal mechanisms. Our experimental investigation has thus paved the way for a distinction between an "attentional" and a "representational" allochiria.