Axis-based grouping reduces visual extinction

We examined the effects on extinction of grouping by collinearity of edges and groupings by :alignment of internal axes of shapes, in a patient (GK) with simultanagnosia following bilateral parietal brain damage. GK's visual extinction was reduced when items (equilateral triangles and angles) could be grouped by base alignment (i.e., collinearity) or by axis alignment, relative to a condition in which items were ungrouped. These grouping effects disappeared when inter-item spacing was increased, though factors such as display symmetry remained constant. Overall, the results suggest that, under some conditions, grouping by alignment of axes of symmetry can have an equal beneficial effect on visual extinction as edge-based grouping, thus, in the extinguished held, there is derivation of axis-based representations front the contours present. (C) 2000 Elsevier Science Ltd. All rights reserved.