Compensatory coding of body part location in autotopagnosia: Evidence for extrinsic egocentric coding.

We report a patient with autotopagnosia (JD) who was unable to code the position of body parts relative to each other and who failed to update the position of body parts after passive movements. JD's performance in Studies 1-4 suggest that her ability to code the dynamic location of body parts with respect to each other ("intrinsic egocentric" spatial coding) was impaired, and that she employed a compensatory strategy by means of which the location of body parts was computed with respect to objects in the environment ("extrinsic egocentric" spatial coding). Studies 5-8 suggest that JD's ability to update hand position information was impaired after passive relative to active movements of her arm. For example, she was impaired in reaching to a target after passive but not active movements of her hand. Taken together, these findings extend previously reported functions of extrinsic egocentric coding to the localisation of body parts and demonstrate a possible dissociation between body part localisation dependent upon proprioceptive and efference copy information.