Tiling pattern of orientation preference. The basic tile of orientation preference, with a singularity at the centre, is shown with the black border. There are two tiling patterns which allow orientation preference to change smoothly across map borders. The upper part of the image shows adjacent singularities which are reflections of each other. This creates the saddle-point pattern. Lower half of picture shows linear zones. The third row of singularities has been shifted across by one column to create this pattern.