A double dissociation between knowledge of object identity and object orientation.

Two patients are reported who demonstrate the independence of knowledge of object identity and object orientation. One patient, with a visuo-spatial disorder, was unable to identify the upright canonical orientation for line drawings of objects, although she could correctly name the objects. A second patient, with visual object agnosia, was unable to name many objects, but could provide the upright canonical orientation--even for objects that he could not name. This double dissociation suggests that information about the canonical upright orientation of objects may be derived both from stored knowledge of objects, and 'directly' from visual information about object structure.