This study will examine whether tactile (touch) abilities at the lip are more acute in people with upper limb amputation compared with healthy normal volunteers. People with an amputated upper limb have an expanded brain representation of the lip that may correlate with heightened tactile spatial acuity.

Normal volunteers will be recruited for this study. Candidates will be screened with physical and neurological examinations. (Amputee volunteers will be studied at the amputee clinic at the University of Tubingen, Germany.)

Participants will sit comfortably in a chair, wearing a blindfold, during the following experiments:

• Plastic domes with grooves are placed on parts of the lower lip on either side for a few seconds. The volunteer is then asked to identify the direction of the grooves relative to the long axis of the lip.
• The participant's arm is placed in a cast and the index finger is immobilized. The same test done on the lip is repeated on the distal part of the index finger.

Each part of the test lasts about 20 minutes, and the entire experiment takes about 2 hours.