Function and manipulation tool knowledge in apraxia: Knowing 'what for' but not 'how'

Several accounts of the semantic system posit that function information plays a critical role in the representations of man-made objects. Alternative possibilities are that man-made objects such as tools are organized according to manner of manipulation, or that both function and manipulation information figure importantly and distinctly in man-made object representations. An agnosic patient, FB, reported by Sirigu et al. (Brain 1991; 114: 727-41) provides support for the latter view, FB was able to demonstrate how to manipulate objects whose function he did not recognize. We now report two severely apraxic patients whose performance, together with that of FB, indicates that function and manipulation information may doubly dissociate, On 'declarative' semantic tests not requiring gesture production, our subjects demonstrate severely impaired manipulation knowledge in the context of relatively intact land, in one subject, perfectly unimpaired) function knowledge. The double dissociation provides further support for the notion that function and manipulation knowledge are critical and distinct features of the representations of manipulable man-made objects.