Change 2D Point Size Clearly

When I plot dots using the following code,the figure show that the dot change unclearly

figure,hold on plot(1.0,5,'O','LineWidth',1,'MarkerEdgeColor','k','MarkerFaceColor','k','MarkerSize',3.0); plot(5,5,'O','LineWidth',1,'MarkerEdgeColor','k','MarkerFaceColor','k','MarkerSize',3.8); plot(10,5,'O','LineWidth',1,'MarkerEdgeColor','k','MarkerFaceColor','k','MarkerSize',4.0);

How to plot points that we could feel the size changed clearly" just like the figure at http://www.mathworks.com/help/symbolic/mupad_ref/pointsize.html

thanks :)"