The two sides of spatial representation in neglect patients: The same spatial distortion for different patterns of performance

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.