Spatial compression in visual neglect: a case study.

In the standard account of left neglect, some manner of attentional boundary is postulated such that elements to the left of that boundary are cognitively neglected. We propose an alternative model in which space is distorted ('compressed') in neglect. A new task is devised whereby the subject must follow 'in imagination' the direction of an arrowhead across 'empty' space to its corresponding position in a numerical target array. The two-dimensional array is Euclidian and all four arrow/array relationships are incorporated (arrow to the left/right of a vertical array, arrow to the top/bottom of a horizontal array). Normal subjects perform at ceiling, with excellent accuracy in all orientations and positions. A patient with severe left neglect (consequent upon lesion of the right temporo-parietal region) shows systematic deflections in her judgement of target positions. These distortions are fully consistent with a model whereby points in 'left space' are compressed rightwards; the compression function is linearly proportional to the coordinates of Euclidian space.