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Patients with neglect show disorders in horizontal space perception. It has been argued that these disorders may depend on a distortion of space that takes the form of a left-right relaxation of the representational medium that becomes progressively "relaxed" toward the contralesional space and progressively "compressed" toward the ipsilesional space (the space anisometry hypothesis). In the present paper we tested this hypothesis by using the Oppel-Kundt illusion that consists of the perception of a filled space as larger than an empty space of the same size. Two experiments were carried out with 14 brain-damaged patients with neglect, 9 brain-damaged patients without neglect and 12 healthy subjects. In the first experiment participants were requested to bisect and read words with different letter spacing simulating the way space is thought to be distorted in neglect. In the second experiment we asked the participants to physically and numerically bisect numerical intervals. The results of the two experiments are in line with the predictions of the space anisometry hypothesis. Specifically, with a background resembling the space distortion proposed by the space anisometry hypothesis, neglect signs are ameliorated in reading words and in numerically bisect numerical intervals, while they are worsened in bisecting words and physically bisect numerical intervals. These results support the idea that the abnormalities observed in typical neglect tests are due to a distorted internal representation of the outside world that takes the form of a mental continuum logarithmically distorted along the horizontal dimension., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Body parts are represented in the brain in a very specific fashion, as compared to other three-dimensional objects, with reference to their prototypic shape and multisensory coding. However, evidence is lacking about the spatial representation of body parts. To address this issue, in Experiment 1 we first compared the metric representation of body parts and of non-bodily objects in 14 right-brain-damaged patients with left unilateral spatial neglect (USN), and in 14 neurologically unimpaired control participants. Participants bisected, by manual pointing, a three-dimensional object, or their own left forearm. Patients showed the well-known ipsilesional rightward displacement of the subjective midpoint, in both forearm and solid bisection. Both USN patients and control participants were overall more accurate in the bisection of their own forearm, relative to the extracorporeal object. In four patients this advantage of the forearm was significant in a single-case analysis, while two patients showed the opposite dissociation, being more accurate with the solid object. In Experiment 2 neurologically unimpaired participants were more accurate in the bisection of a fake forearm, as well as of their own forearm, as compared to the extrapersonal object. Overall, the results indicate that the representation of the metric of the body is more reliable than that of extrapersonal objects, and also more resistant to the disruption of spatial representations brought about by USN, possibly due to the prototypical shape of body parts. Furthermore, the double dissociation found in USN patients suggests that the metrics of body parts and of extrapersonal objects are supported by independent spatial processes.