This figure is part of Activity 5 Adelson’s checkerboard illusion. This picture shows a 5x5 checkerboard with a green cylinder in the top right corner which casts a shadow to the bottom left of the picture. The second square in the top row is labelled ‘A’ and the third square in the middle row is labelled ‘B’. ‘A’ appears considerably darker than ‘B’. At the left and right of the figure are arrows that can be clicked on to introduce parallel vertical lines. The lines show that ‘A’ and ‘B’ are in fact the same shade.