Weight Discrimination Using an Upper-Extremity Prosthesis

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A person with an upper-extremity amputation who uses prosthesis often engages in prehension activities that require the grasping and manipulation of objects. As a result of the amputation, such prehension activities are clearly performed with a significant loss of proprioceptive information. It has been shown in the psychophysical literature that losses in proprioceptive information impair both perceptual judgments (such as weight discrimination) and motor function in nonamputee participants. It is not known whether similar impairments occur with users of upper-extremity prosthetic devices, therefore two experiments were performed to investigate the ability of individuals using an upper-extremity prosthesis to discriminate weight of hand-held objects. In the first experiment, we compared weight discrimination of nonamputees using either their anatomical limb or a simulated upper-extremity prosthesis. In addition, we included a person with a congenital limb deficiency who was an experienced prosthetic user. The results revealed that weight discrimination was poorer with the simulated prosthesis than with the anatomical hand. Surprisingly, there were no significant differences between the anatomical hand condition of this group of participants and the person with a congenital limb deficiency. In the second experiment, we found that withdrawing visual information from the same person with a congenital limb deficiency did not degrade the ability to discriminate weight. These results suggest that experience using a prosthesis may overcome the initial difficulties in discriminating weight. Discrimination may improve because the experienced prosthetic user learns to rely on other sources of proprioceptive information in making perceptual judgments and/or because the user develops greater control over the prosthesis.

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