The effect of tactile feedback on pantomime of tool use in apraxia

Objective: To investigate whether apraxic patients' better performance with real tools compared to miming is due to the tactile feedback provided by holding the tool. Methods: Ten patients with aphasia and apraxia from left hemisphere damage were asked to demonstrate the use of 12 tools and objects under three conditions: miming with empty hands, miming with an implement shaped like the handle of the tool, and using the real tool with its corresponding object. Results: Whereas real tool use was much better than pantomime in all patients, tactile feedback from the isolated handle facilitated miming only in some and deteriorated it in others so that across the group there was no significant improvement. Conclusions: The better performance of real than of pretended tool use does not depend on tactile feedback per se, but on the mechanical affordances and constraints of tools and objects transmitted by this feedback in real use. Tactile feedback deprived of these contents and restricted to the shape of the handle does not substantially help produce the appropriate action.